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Hi All--

OK, one more time--I have tried some of the tests suggested previously; I started out on the highway. After about 5-10 mins, the temp had climbed close to the double lines, but didn't enter that area. As I saw it nearing that area, not knowing if it the fan would kick in, I pulled over before , shut off the engine for about a minute to let the engine compartment heat up, turned it back on, and the temp began to drop. I had to do this a couple of times. I did notice that I definitely could not keep my hand on the top of the radiator. I will add that I did not keep driving to see if the clutch would kick in before the temp actually entered the danger area

I also noted that, once off the highway and on the mountain roads, where my speed fluctuates quite a bit, the temp would sometimes get close to the double lines, drop down, and at one point actually went below the half way mark--would this be due to less air flowing through system, and compartment getting hot enough for fan to kick in?

ALSO JUST NOTICED: this morning, I looked under hood--plenty of coolant in reservoir, but BOTH top and bottom radiator hoses appeared to be "sucked in" or collapsed; when I took off the radiator cap, that was a vacuum release, and the hoses returned to normal...

the cowl seems to be in place, but there is a screw missing from the bottom--could a loose cowl be allowing too much air flow and keeping fan clutch from kicking in?

Or, if air flow is being obstructed (there is a tranny cooler mounted in front of radiator), could the fan clutch be kicking in, but not able to properly cool?

I also tried turning on the heater w/blower off, but that didn't seem to have much effect either way

I also noticed, though, when starting the ending cold, to see if the coolant was flowing properly, it began to rise and overflow after about a minute--I was watching for some sort of bubbling or indication of flow, but didn't notice any, Yet, the coolant does seem to be flowing, since, as I say, I got through the 90 mile drive without actually overheating

I had the temp gauge checked, and it seems OK; I put in a new fan clutch, new radiator, and thermo (though this may be a 190 rather than 160)

Could this be a combo of things? when the coolant gets hot, does it flow better? should I have the block flushed, put in a lower temp thermo, and perhaps replace the FC again? should I do nothing and just consider it "normal"?

These drastic fluctuations in temp are nerve-wracking. Could any of this indicate a head gasket issue?

Again, this is a Nissan V6, if that matters

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I don't know about the Nissan, but on my Toyota, I can hear a big difference when the fan clutch kicks in. it not loud or obnoxious, but the "roar" of high speed air is definite.

Also it takes a couple seconds from no clutch to full clutch on mine

Did you heater throw out really hot air when you turned it on?

It almost looks like the fan clutch, but I don't know anything about the Nissan fan clutch.

John Mc

88 Dolphin 4 Auto

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the collapsing of the hoses when cold makes me think the fluid isn't flowing from the reserve tank to the radiator when cooling. the reserve tank level should lower when cool, raise when hot. should be able to just let it sit and idle and see if the tank level changes and if the fan comes on, unless you are in a cold area. maybe the line from the reserve is kinked or plugged, disconnect at the radiator and see if fluid flows out of the tank. in many cars when you turn on the air the fan comes on regardless of temp. i just don't believe it should be running that hot. check to be sure automatic trans is full, maybe too much heat coming from the trans cooler??? when you warm it up with the radiator cap off and the water bubbles out doesn't seem right either. I've watched the fluid flow through the radiator with the cap off, not bubbling out. maybe air trapped in the engine?? when warm try squirting water on the front of the radiator, if temp drops quickly maybe airflow is a problem do to plugged or fan not coming on when it's supposed to. if the main radiator hoses weren't changed with the radiator maybe they have collapsed inside restricting flow??? just thinking out load.

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Tlava - Have you googled or looked thru any Nissan groups.

I'm not saying this is the problem, but there are engines out there that have special "purging" procedures for coolant systems. the engine can have a huge air bubble inside and it will stay there forever unless you do this special "purge". I used to have a Chevy like this.

Just a thought, google the engine you have along with something like "coolant system purge" and see if anything comes up.

John Mc

88 Dolphan 4 Auto

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Thanks again for more info--I just happened to think about the simple possibility of the reserve tank hose being blocked. I'll check that. Yes the heater was on full and blows hot. There is the AC evaporator and then the tranny cooler mounted in front of radiator, but it seems more that the fan is not engaging as it should, since it spins rather freely when hot at first. I'll try the water squirt, though--;like with a squirt bottle, or a hose? through the very front (grill)?

SOunds like not a bad idea to have the block flushed anyway? Though, as I say, the water is getting plenty hot, which would suggest it is circulating, just not cooling down? a blockage in the block wouldn't casuse that, right?

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I assume this is a mechanical fan, attaches to your water pump thru the thermo clutch.

I think your clutch isn't engaging properly.

When the engine is hot, very hot ( like getting ready to over heat), if you pop the hood and rev the engine, it should be blowing a lot, I mean if you do a quick rev it should blow your hat off, and the air should be hot.

One item to consider, I did this when I was broke and couldn't afford the thermo clutch, i bypassed the clutch, they sell a small aluminum block that you can use in place of the clutch.

The fan will run all the time. if this solves the cooling problem then you defiantly have a clutch problem.

Although there may be a problem with your system sucking coolant back in from the overflow, I don't think this is a factor in your heating problem.

John Mc

88 Dolphin 4 Auto

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Hi John--

Not sure what the thermo clutch is, but I believe the fan has a fluid in it that thickens as it heats? It has a coil on front, like the old mechanical furnace thermostats...in any case, it attaches directly to a pulley driven by I believe the same belt that drives the water pump

Would the hoses snap back into place without removing the cap, once the engine is started? Anyway, certainly not normal, I guess.

IF it is the fan clutch, wonder what gives, since it is a new clutch.

wondering if possible to install an electrical fan (this is an '86--not sure where it would go or how it would fit/mount.)

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Three thoughts...you might of put your themostat in backwards, your themostat is defective (does happen to new ones),

or your themostat is set too high (you stated you might be 30 degrees hotter). I test all new themostats on my kitchen

stove, put it in water with a temp gauge and wait and watch for it to open at the stated temp.

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Tlava -

Thermostat

BufBooth brings a good point about the thermostat, If its bad or backwards, this could cause the problem. I'd just remove it and see if this resolves the problem. (You said the radiator is very hot (can't leave hand on it) so I tend to think your getting coolant flow OK thru the radiator.

Hoses

Yes, they will as pressure builds up, However, there is a chance that the bottom hose could be collapsing because of the suction from the water pump. This becomes less likely as pressure builds up as the pressure in the coolant system. Then I come back to the hot radiator indicates that there is flow.

Fan Clutch

Every thing seems to point to the Fan clutch ( I called it the thermo clutch) is not engaging. On the Toyota, this is a fluid that gets thicker/thinner and engages the clutch. on some others, I see a bimetal spring that does this.

Did you replace the clutch or did someone else do it. Google the fan clutch afor your model truck and see what comes up.

Electric Fan - yes its possible, I see discussion on this, but don't know of anyone whos don it and reported back. (I've been tempted to do this myself)

John Mc

88 Dolphin 4 Auto

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OK Tom here goes. For starters your thermostat is unusual in that it mounts vertically on the engine. This prohibits filling the engine with coolant before it is installed cause it would just run out of the system. Also this thermostat has a vent at the top if it is installed correctly to help get bubbles out of the system. I'm guessing maybe yours doesn't have that vent because it is the wrong thermostat. It has to be or it wouldn't be 190. Factory stats for that engine are a 155 degree thermostat. Yes that is very low but that is what my Nissan factory service manual says and I told you this months ago. Just remove it. When you refill the coolant put a large funnel over the radiator hole. Pour coolant in until it comes up in the funnel a bit and start the engine. keep and eye on it and when it doesn't suck anymore in after heating up all the way you are done. Put pan under radiator because when you pull the funnel off some will spill. Put your cap on and your done. With a thermo requirement that low I don't think you need one even in New York. Just sit for a few minutes after starting and it will already be at driving temps. So all this cost you nothing and it will probably fix the problem. if it still overheats you will know next time that it is the fan clutch. Possible that the same bad mechanics that installed the wrong thermostat , installed the wrong fan clutch too

Linda S

By the way guys I own a Nissan Sunrader identical to Toms so I do know what I'm talking about

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I actually had not seen the toyhomes with the nissan vg.

But I'll tell you that the 300zx uses a twin cam version of the vg and most parts and accessories are compatible with the trucks. like huge oil filters and huge fuel filters and radiators etc.

my 89 truck I had for years had 300zx seats and a shift knob. And the oil filters which are enormous almost like a semi.

the early maxima uses the vg also.

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Hi LInda, John, and all--let me make sure I understand. First, yes, I installed the new fan myself, but there didn't seem to be any special procedure there--just remove the nuts and put the new one in (a bit tricky since not much room to work) the instructions did say to torque a certain amt, which I just estimated since I could only fit a small thin crescent wrench into the space--but the torque wouldn't effect the operation of the clutch, right--the nuts just secured the fan to the pulley

So Linda if I want to get the right thermo, where/how? do you have a source for that, or can I just ask at NAPA, or wherever, for a 160 thermo? but how can I tell if it is the right one with the vent? the one in there now is probably whatever the parts store suggested. Also, if water is hot, wouldn't this indicate the thermo is opening OK?

Otherwise, I should remove it, put everything back together, then refill with coolant through the radiator top hole? The one thing I did notice though as I said the fluid right now pushed up out of the top hole almost immediately, before the engine is warm...

Thanks again for all advice!

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I work for a company that designs engineers and makes Fan clutches and fan drives. I can tell you these things about them:

The viscous fan clutch that is driven by the engine spins more and less frequently by the presence or lack there of of fan drive fluid inside the clutch. the bi metal spring you see simply turns more or less with the temperature and in turn opens a valve to let the fluid flow into the clutch jaws. if you were to take a band saw and bisect the clutch you would see the plates are like teeth with fluid entering and filling the gaps of the teeth. the presence of the fluid causes the fan to spin; the absence of it causes it not to spin as much. Its that simple. electric fans can NEVER deliver the torque and air flow that clutch drives can. Our newer clutches have electronically controlled clutch reservoirs instead of the tried and true bi-metal governed ones but the concept remains the same. the bi-metal spring when cooled will close the valve that makes the fluid spin out of the teeth.again, when hot it opens, sending the fluid back in. So what can go wrong on a fan clutch? not much I am afraid; there are only two things really:

1.) stuck valve (leaving it always on or always off or in between) 2.) fluid viscosity breakdown, retarding performance but not ending it 3.) liner or seal failures where fluid escapes leading to a drive that behaves like its always off even though it valve is still working.

Fan drive clutches are non repairable; if you have a dead one you must replace it with a new one. Having a fan on all the time at worst robs the engine of power necessarily and at best takes it longer to warm up in colder weather.

-MB

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don't have a nissan, but, if the fan clutch was part of the fan so would the pully be part of it? if so sounds like only the fan was replaced. i would start with the easiest, just remove the thermostat completely and test it. running and engine without one, unless weather below 60 degrees or so won't effect it much, as pointed out, just take a little longer to reach operating temperature. if that solves it then figure out what the right thermostat is and get one. do one thing at a time and test it, makes trouble shooting easier and probably lest costly in the long run. from linda's description of the thermostat, having a hole in it that goes toward the top, the right one should be easy to spot. maybe the old one is still laying around somewhere??? hasn't been dumped yet???

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Tlava -

Thermostat

BufBooth brings a good point about the thermostat, If its bad or backwards, this could cause the problem. I'd just remove it and see if this resolves the problem. (You said the radiator is very hot (can't leave hand on it) so I tend to think your getting coolant flow OK thru the radiator.

Hoses

Yes, they will as pressure builds up, However, there is a chance that the bottom hose could be collapsing because of the suction from the water pump. This becomes less likely as pressure builds up as the pressure in the coolant system. Then I come back to the hot radiator indicates that there is flow.

Fan Clutch

Every thing seems to point to the Fan clutch ( I called it the thermo clutch) is not engaging. On the Toyota, this is a fluid that gets thicker/thinner and engages the clutch. on some others, I see a bimetal spring that does this.

Did you replace the clutch or did someone else do it. Google the fan clutch afor your model truck and see what comes up.

Electric Fan - yes its possible, I see discussion on this, but don't know of anyone whos don it and reported back. (I've been tempted to do this myself)

John Mc

88 Dolphin 4 Auto

All mechanical clutch drives contain fluid. Its not the fluid that gets thicker or thinner its whether or not the fluid is in the clutch or pumped out by centripetal force and centrifugal force. :-)

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I am not sure of all you have done already, but I would suggest that you just remove the thermostat as a test, and run the engine and see if it still overheats, if it does, then you know it's not the thremostat. Did you say that you replaced the radiator? If you have not, sediments and corrosion at the bottom of the core can keep the fluid from flowing, as it can look clear on top, but be plugged at the bottom. You did check your water pump? Sometimes the impeller inside detatches from the spindle rod. Running too lean can cause the engine to run hot even if all the fluids are flowing properly, and an exhaust leak at the manifold can do the same, especially if the leak is near the temp sending unit. I hope you get it figured out. Happy Travels!

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I have not tested the water pump; but the sending unit sounds like a possibility? I just took the Sunrader to a mechanic. He put a temp gauge into the water, and said that the thermo seemed to be opening as it should at about 187%; he also said that the temp gauge inside the cab was reading up to the double lines, yet the water was only 185-187, and suggested that perhaps the sending unit was sending false information to the gauge? I didn't ask him directly, but he seemed to imply that the temp stayed at 185-187, or maybe dropped a little, but definitely wasn't overheating, even though the temp gauge suggested to was... I don't know...

still, if the fan clutch were working properly, shouldn't the water temp drop down below 185-187? Also, as I said, when I pull over, shut off the engine, that turn it back on again, the temp gauge does respond, and begins to drop....

About getting at the thermo: I guess Linda may have to answer this: do I have to remove the fan, the pulley above it, and the timing cover to get at the thermo, or can I get to it just removing the air cleaner and related apparatus directly over it....

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if the mechanic you took it to knows what he's doing, your sender unit is wacko and your gauge isn't telling you the truth, you really aren't running hot. the other is the gauge itself has gone bad. i think i would not be doing anything else or spending any more money except to replace the sending unit and see if the gauge is working. surprised he didn't try to sell you on replacing the unit for you. hope he's a better mechanic than salesman.

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Some thermostats you can not leave out I think you may have a two stage stat it will have a button on the bottom about the size of a quarter that closes off the water bypass port when it opens. Your rad cap has a small brass valve on the bottom that allows the coolant to be drawn back into the radiator as the engine cools from the capture tank if the hose is collapsing there is some thing wrong with the capture tank/hoses or the cap. The clutch fan moves lots of air if it’s hot even at idle you should feel a good breeze behind it.

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Not if the thermostat is doing what it's supposed to. You don't really want it any cooler than that anyway.

... shouldn't the water temp drop down below 185-187?

I don't know what thermostat is supposed to be installed in your Nissan VG30i engine. For the Toyota, the 22R-E is 190F, the 3VZF-E is 180F. These are the temperatures that the thermostats start to open. Full open ~20F later.

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Does anyone know where the sending unit is, what it looks like, and whether I can get to it on this engine?

It's funny, though, since a previous mechanic put a sensor on the block, and said the temp seemed basically to match the position of the needle on gauge, and that the gauge was accurate... of course, he didn't check the temp when the gauge was in the hot area. I think the block temp was about 160% when he checked it, and the gauge was more or less in the middle? Sot it's possible that as the engine gets hotter, the gauge begins to lose accuracy? some sort of error related exponentially to heat?

I did buy a new radiator cap in a small town I was passing through... but who knows. I squeezed around on the tube to the tank, and it doesn't seem there are any blockages (also some fluid runs out when I take the submerged end out of the reserve tank).

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Here is a page that shows where the thermostat is, how to change, and where the sending unit is.

http://www.autozone.com/autozone/repairguides/Nissan-Pick-ups-and-Pathfinder-1970-1988/ENGINE-MECHANICAL/Thermostat/_/P-0900c1528004f193

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THanks for the link--the Nissan V6 is a different animal, though, when it comes to getting at the thermo. But your suggestion is the the sending unit shuold be in a similar spatial relationship to the thermo, regardless? Or might it be in a totally different place on the VGi?

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Hey--anyone out there close to Andes, NY (Catskills--about 50 miles west of Kingston on I 28)? If so it i could drive out to meet and actually look over this in person, it might be a great help (reward for whoever solves the problem!--ha!)...

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Sending units are located in various areas on different engines, but usually on a water jacketed part of the block. Many are near the water pump, some by the thermostat, but they usually have a similiar look. They for the most part are just a simple fitting that will usually have a large nut fitting at the bottom where you use the wrench to remove and install. They screw directly into the block, manifold, or head, they have two wires coming out of the top of a connector that usually snaps to the sending unit, although on some older non computer controlled engines, they might have one wire using the block as a ground. Any auto parts store, garage, or mechanic can show you where yours would be, and which is the correct one for you.

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thanks David--I do see something stuck directly into the top of the manifold, perpendicular to it (i.e., mounted vertiaclly), close to where the main hose from the radiator connects to the block (though I assume the thermo. itself is located further down on the block, since another hose splits off from the main hose at that point and dips down into a quite hard-to-see/get to place?). The part that looks like the sending unit is right under the air cleaner apparatus, and fairly small--maybe about a 10mm nut on it--with a wire coming out and feeding into the main wire harnace--could this be the sending unit?

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More than likely, since it is going into the water hose area of the engine. Depending of the year, and if EFI, there are some sensors that do go to a computer, and even on my electric adjusted carb there are sensors for load and choke adjustments. I have given a drawing I made of what a typical sending unit relatively looks like. In all honesty, these are very basic items, and think if you have an Advanced Auto, Auto Zone, NAPA or any good chain of auto parts stores in your area, they will have all the research books and knowledge needed to locate where it is, and find the part in their database. Good luck!

post-5603-0-18338600-1345569169_thumb.jp

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I was able to remove the temp sensor--the thing looks so basic, hard to believe it would go bad; I'm wondering if maybe someone had put the wrong one in? maybe meant for the 4 cyl rather than the 6? could that cause a too hot reading?

I will replace it, and see what happens...

should the threads be treated? I use Harvey Seal thread compound on LP and plumbing fittings--good up to 6,000 psi on gas fittings, and up to +400 F, so should work well in this application...I swear by this stuff--never use teflon tape...

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I was able to remove the temp sensor--the thing looks so basic, hard to believe it would go bad; I'm wondering if maybe someone had put the wrong one in? maybe meant for the 4 cyl rather than the 6? could that cause a too hot reading?

I will replace it, and see what happens...

should the threads be treated? I use Harvey Seal thread compound on LP and plumbing fittings--good up to 6,000 psi on gas fittings, and up to +400 F, so should work well in this application...I swear by this stuff--never use teflon tape...

Great! Now all ya need to do is go to the auto parts store, give them your year, model, and engine size, and they can reference match the one that is supposed to be in the motor. Even if the one you have is incorrect in hand, they shouldent need it determing the actual and proper sending unit needed, they have books and computer listings for that. I would ask them if any application to the threads are needed. Good Luck!

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Hi All--

well, I replaced the temp sensor, and that may have been the problem... will know for sure after taking a drive, but I let the engine run qute a while and temp read below half...

one concern--the nut on the sensor does not screw down flush with the manifold--it is snug, though, and I didn't notice any seepage of coolant--is this correct?

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There should have been a soft washer at the base, and that might make it appear as if it isnt seated to the nut, but the washer should be snug to seal the fitting. Glad you were able to get your problem resolved! Great job!

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oops--there was not washer with the replacement part... don't rememer one on the old part, though there was apparently something--remains of something on top of manifold; I assumed it was some kind of sealant... well, I didn't notice any seepage-do I need to take all apart again and find a washer? but where would I find this washer? As I say, the new part came without one...

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oops--there was not washer with the replacement part... don't rememer one on the old part, though there was apparently something--remains of something on top of manifold; I assumed it was some kind of sealant... well, I didn't notice any seepage-do I need to take all apart again and find a washer? but where would I find this washer? As I say, the new part came without one...

Not all sensors are designed the same, I think that if it is tightened all the way, and it is not leaking after running for awhile, you are good.

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