1991 GT-R overheating

[Jjtxaz24]

What's going on guys? I have a 1991 GTR and just got it. Its currently overheating and when it does the oil temps get up there too.

I tried to search but didn't see the issue i was having. I have a theory on what it might be but I'm going to wait and chime in when you gurus reply.

Hint: thinking its the water pump because oil temp and coolant temp go up at the same time, meaning its not circulating as it should. Gets so hot it starts to boil.

[Duncan]

Well firstly, congrats on picking up the new car! 91 is an unusual year, was it Australian delivered?

As for the overheating, unfortunately there are a lot of potential reasons and not enough info to really guess.

If it overheats when stationary (unusual on these) it suggests some problem with the viscous coupling on the fan, these wear out but generally seize to be on all the time

If it overheats based on time or load when driving there are a lot of things to check and you may want a mechanic to do them

-air lock somewhere from coolant not being bled properly. rebleed the system including having the heater on full and opening the bleed on the intake manifold near the injectors, and using some sort of bleeding funnel. If the car had been serviced by someone who wasn't careful this is the most likely issue.

-thermostat not opening, this will make it overheat pretty quickly but is an easy fix

-leak in the system. run a pressure test and make sure there is no issue. another symptom here will be coolant loss. Leak could be in the radiator, hoses, heater core, radiator cap not holding pressure. Potentially and expensively but unlikely, it could also be a head gasket or block crack.

The water pump itself can't fail to pump as it is belt driven from the fan/water pump/alternator belt. That should be obvious if missing....when water pumps fail they leak from the seals

[niZmO_Man]

Oil temp goes up because water cooling system isn't working properly. First I'd flush the system (take out radiator, flush that, then flush the block). Also check your clutch fan, it should spin with resistance (engine off), and you should hear it turn off after a bit when you first start the car cold, and engage (go loud) when it gets hot.

[Jjtxaz24]

Appreciate the help guys. 

Pulled out the thermostat and tested it. It appeared to be working, found a replacement at a parts store off a 95 300zx so minus well change that out since I was already in there. 

Next up is the clutch fan. I remember spinning it but it didn't seem to put up much resistance, trying to find one locally (I'm located in Texas) I looked around and read a 1991 Pathfinder clutch fan works. Do we know if this is accurate?

[Duncan]

Ahh that will make it a bit trickier.

Not sure about the pathfinder option, here we generally use rb30 skyline or patrol as the cheap but compatible replacement.  The good news is it only has to fit physically so if you take yours off you should be able to compare.

Did you flush it out thoroughly, rebleed everything properly and do a leak test? Chasing and changing parts is doing the hard things first.

[Jjtxaz24]

Good news guys, I was able to locate a 1995 300zx thermostat. Although it is a bit shorter from the top the rest of it is identical to the stock nissan one. Ill attach a picture just for a reference. 

When I pulled the old one out, it read Nissan on the top. So it may have never been changed, either way I needed a new one. 

Cleaned up the clutch fan as well with some WD-40 on the little coil part and a wire brush. That gave it back some resistance when I spin it. Used this video as a reference: 

 

Anywho, used the manual and refilled the coolant, and topped it off. Drove around for about 40 minutes with some spirited driving, freeway, and put myself in some stop and go. Temp stayed at halfway and my oil temp was good too. Im pretty sure its fixed.

Thank you guys for the help.

[niZmO_Man]

Probably just needed a good flush and bleed.

[Jjtxaz24]

1 hour ago, niZmO_Man said:

Probably just needed a good flush and bleed.

Yeah I think so too. Replaced the thermostat since i had already gone through the BS of taking the old one out. 

[TXSquirrel]

If you are in Texas, may consider getting a new radiator if you are still running on factory one.  Both Koyo and Mishimoto offer reasonably priced replacements.

As for the fan clutch, if I recall Infiniti Q45's can work but not exact.  There was an discussion about interchangeability on Rivsu's old forum before they went out of business.  From what I can remember, almost all the late 80s and early 90s Nissan clutch fans share the same bolt pattern but vary a few mm in height, and unfortunately there is not one with the exact height as R32.

Edit:

Here is an old picture I found, not exactly sure which car this came from, could be a Z32.  So the unknown new fan clutch is the exact same height as R32, but somehow the base is 2mm thicker and so the nuts could not be tightened through all the threads.  

 

Edited April 16, 2019 by TXSquirrel

[Jjtxaz24]

Did some driving around and its been a couple of days with no overheating. Drove it to work today and noticed this happening. 

I was parked here but I usually notice it at lights on stop n go traffic, etc...

What were looking at is when I press the brake in the needle in both gauges will rise, when i let it go they will drop. Do you guys know why that is?

[Duncan]

Looks like she's l running a bit hot (noting it may well have been a hot day there...)

That movement in the gauges must be a minor electrical issue.....either a bad (common) earth, or gauge power circuit, or even battery terminals. I haven't seen it before but I wouldn't be worried.  Does the volt gauge work (and, does it move when you put your foot on the brake?)

[Jjtxaz24]

2 hours ago, Duncan said:

Looks like she's l running a bit hot (noting it may well have been a hot day there...)

That movement in the gauges must be a minor electrical issue.....either a bad (common) earth, or gauge power circuit, or even battery terminals. I haven't seen it before but I wouldn't be worried.  Does the volt gauge work (and, does it move when you put your foot on the brake?)

Yeah its a little hotter today here than it has been. My volt meter does work and it reads just above 12 volts. It doesn't move when I press the break. 

I believe it when you say it might be a bad ground or wiring issue. Noticed it flinches very little with the blinkers on as well. Car needs a good scrubbing down in that engine bay and grounds redone. 

I have the ground (negative cable) from the engine to the negative battery terminal and about halfway to the battery is another grounding point (not grounded) Do you know where that goes too on the chassis?

[Duncan]

That is very likely to be the issue if the main battery earth is only connected to the engine.  It should go to the chassis first just near the battery (above hicas pump if you still have it), just an m6 thread that you put a bolt in. Let me know if you can't find it, I'll try and get a pic although my setup is a little non standard.

[Duncan]

BTW healthy alternator should be charging the battery at something around 13.8v so 12 is not right. Noting the standard gauge is hard to read properly.

If you have a multimeter check the voltage across the battery when the car is running.

[Jjtxaz24]

4 minutes ago, Duncan said:

BTW healthy alternator should be charging the battery at something around 13.8v so 12 is not right. Noting the standard gauge is hard to read properly.

If you have a multimeter check the voltage across the battery when the car is running.

Ill check the voltage when its running. Ill do that. Let me go look and see if i can see where the negative gets hooked up too. 

[Jjtxaz24]

I took the car on a spirited run and it overheated on me. Coolant was at the top line just under the Hot. Shut it off, let it cool and limped it home. I dont see any leaks but its so hot is boiling the coolant and spilled into the overflow tank.

Car was running good. Drove it Tuesday and friday with no issues. I wonder if me driving it hard is what gets it to overheat. When i drove it tuesday and friday i just cruised with some random little spurts but mainly cruised to and from location. 

Im gonna invest in a radiator and currently my condenser fan doesn't work or isn't engaging/turning on. Is that just for AC? Could that be an issue as to why its overheating?

I appreciate your guys help. 

[TXSquirrel]

I don't think I have seen my oil temp gauge gone up that high since I have owned mine, even after multiple pulls on the dyno.  I highly recommend a thorough coolant flush and a proper bleed (there is small bleed valve on the head near fuel rail).  Maybe throw in an oil change too, it's cheap insurance.

Yes as far as I know the condenser fan is only trigger by A/C.  You can wire it to run from a toggle switch to help cooling, but that still won't solve your core issue, plus your electric system doesn't appear to be 100%.  I Google a little more and the fan clutch I posted above is from Infiniti Q45, so feel free give that a try since it's only a $50 part from any local part store.

As for your electrical issue, other than sorting out the grounds, a new alternator is definitely helpful.  Circuit Sports offer a new direct OE replacement and they are reasonably priced.  

[Jjtxaz24]

Alright, update time. 

Went out and bought a fan clutch for a 1991 Z32, it was the same as the one for the infiniti Q45. Flushed the system and replaced the coolant by undoing both upper and lower hose and removed the radiator and cleaned it out with water from the fill and it trickled all the way to the lower. 

I used this to flush the coolant and refill it I did NOT remove the block drain plug. 

 

I did notice that part of the refill procedure for the coolant there is a step that says to check the lower radiator hose to see if warm coolant is passing through. When my upper hose is warm, the coolant in the lower hose is not. 

It also states for you to check the thermostat injection valve (step 7, on the service manual screen shot in the thread above). What is that? The thermostat? 

I also check my grounding point cleaned it up and bolted it down. Voltage and flickering on the gauges it gone gauge reads at the 14 volt mark and the Alternator is new, pushing out the required volts. 

Also, I went out and got some fresh oil in the car. Read up everywhere and saw it takes 4.5 quarts of oil but not to be afraid to use 5. I used 5, 10w30 full synthetic Mobile 1. 

Drove the car around again, coolant temp is good half way but once my oil temp gets to the halfway mark (referenced picture was the 1st time before I changed out the oil) that's when my coolant temp just starts climbing. 

Waiting on payday, last thing I can think of that I haven't replaced is my radiator, after the radiator swap I'm out of options on what it is if that doesn't fix it.

[Jjtxaz24]

Just thought of something...

When refilling the coolant and it ask to feel the lower hose and it doesn't feel warm when it should, it might be the new thermostat I bought is/went bad, or worked and stopped working. 

I have bought parts from a parts store and having them fail a week later. It was a 300zx thermostat. 

[TXSquirrel]

Hmmm sounds like you have all the basic maintenance covered.  I am sure you have checked them, but your fan, fan blades, and fan shrouds are all in good shape?  And you already replaced your water pump right?  

I notice your oil pressure is looking a bit low, but that could be because your oil was running so hot and viscosity decreased.  Mine sits at ~4 during idle.  Hopefully other can chime in on this, and hopefully that's not a sign for a bad oil pump.  (However, oil pressure sender is known to go bad, could be as simple as that.)

As for the radiator hoses, the lower hose is supposed to be cooler than upper hose.  (I have a laser thermometer that I can measure the delta next time I take my car out.)  But are you talking about a big temperature difference between the upper and lower or the lower not warm at all?  If so then I am drawing a blank since you already flush your radiator...

Like you said, maybe try another thermostat.  It's been around 85°F here and a healthy factory radiator should be able to cope with that.