Overheating woes

[Gnnr]

My car is a mystery.

First off, its 95 stock auto 240sx.

Now, I've been running without a thermostat for almost a year now. When I had a thermostat in I would overheat. Running without one though I would be fine. But doing so causes the engine to run in open loop, which gives really really shitty gas mileage and the car feels like ass. Since I've been running fine for so long without a thermostat, not overheating at all, and gas prices are so high and I'm trying to do I can to get the best possible gas mileage out of my car (its my daily). I figured I put one in so I can improve my gas mileage.

So I bought a new thermostat from the dealer, put it in, and again I rapidly overheat. Without it I'm fine though, so that makes no sense. If it where a blown/warped head it would overheat with or without it, wouldn't it? Same thing if it where the water pump I wold think. No signs of a blown headgasket (oil in coolant or white smoke) has shown. The radiator is new and so is the cap. No leaks that I'm aware of. Using the electric Taurus fan on high and using 50/50 coolant. Whats left? Maybe the stock thermostat opens too late. Should I try a Nismo thermostat? I don't know. I'm lost. :confused:

[umsports]

Take out the actual spring and thermostat part of the thermostat and run it like that. http://img337.imageshack.us/img337/4999/tstatrestrictortncl0.jpg (http://imageshack.us)

[hipro]

For some reason, most after market and Nissan stock thermostats are set to open at around 170 degrees F (72.5 degrees C). For my '95, I had the same problems until I bought one of the Nismo lower temp thermos. It is designed to open at 144 F (62 C).... worked for me. Do a web search for Nismo lower temperature thermostat or go to http://www.nismoparts.com/catalog/?section=619 (about $54). I believe mine cost about $50 compared to the $10 everyday variety. Hope this helps.

[ladiesman8527]

make sure your cooling system is bled completely. im just throwing out ideas. your oem thermostat should be good enough though. did u make sure when u installed the thermostat that the jiggle valve was at the top? i dont know if that would make a big difference.

[Gnnr]

Take out the actual spring and thermostat part of the thermostat and run it like that. http://img337.imageshack.us/img337/4999/tstatrestrictortncl0.jpg (http://imageshack.us)

Forgot to mention that thats the way I had it. With the spring cut out when I was running without the thermostat.

For some reason, most after market and Nissan stock thermostats are set to open at around 170 degrees F (72.5 degrees C). For my '95, I had the same problems until I bought one of the Nismo lower temp thermos. It is designed to open at 144 F (62 C).... worked for me. Do a web search for Nismo lower temperature thermostat or go to http://www.nismoparts.com/catalog/?section=619 (about $54). I believe mine cost about $50 compared to the $10 everyday variety. Hope this helps.

I guess I'll have to give that shot. Thats kinda pricey for a thermostat, but I'm out of options at this point.

make sure your cooling system is bled completely. im just throwing out ideas. your oem thermostat should be good enough though. did u make sure when u installed the thermostat that the jiggle valve was at the top? i dont know if that would make a big difference.

Yes, I installed it with the jiggle valve at the top. As far as bleeding, even if it was bled incorrectly, why does it only do it with a thermostat? Wouldn't it also overheat without one if it had air in the system? This was the second thermostat I bought new from the dealer just to make sure I didn't get a defective one the last time I tried to get this whole thing working.

Thanks for the replies. Anymore thoughts?

[jmauld]

Might be a little easier to bleed without the thermostat in place.

[g6civcx]

Test the thermostat by suspending it in a pot of boiling water (hang it on a string from a chopstick to keep it from getting too hot at the bottom of the pot) and a temperature gauge. It should start opening around 150-160, and should be fully open at 180.

It may be that you bought a couple of bad ones. Start with that and see how it goes.

Your problem is really weird though. How do you know you're overheating? Don't trust the stock temp gauge. Get a real gauge.

[Big Bronze Rim]

The car *should* work fine even with a stock temp thermo. My guess is that a) its probably not an OE thermo - the cheap auto parts place ones can be very hit or miss and you can get one that wo't work correctly
b) You are not bleeding the system properly with the thermo installed, and without the thermostat in the car, its bleeding ok and thus the car isn't overheat.
I would do what g6civcx suggested and test the thermo you have, if it checks out ok, reinstall it and try bleeding the system again. If you ask two different people you will probably get two different methods to bleed the coolant system, but I like to park the car on a hill, pull out the bleeder screw while filling the rad with a hose, wrap a towel around the hose and the rad opening and semi-pressurize the system. Water and air will then spray out of the bleed hole. I learned this trick from a friend that, at the time, worked for C&R radiators. We used this method when we did our radiator testing a few years ago. Once you have a nice stream of water I usually repace the bleed screw and start the car. Make sure the heater is set to full hot and let the car warm up. As the thermo opens you may need to add a bit of water/coolant. Cap it and go drive.
And like mentioned GET A REAL TEMP GAUGE as the stock one is absolutely useless.

[AceInHole]

Do you have to refill coolant often? Blowing coolant into the overflow tank? My guess would be a blown headgasket, or something leaking at temp. Otherwise how is the radiator cap?

I recently had a problem where I blew my headgasket. It was sealed when things weren't expanding too much, but heat and pressure would cause cylinder compression to leak into the coolant system, blowing coolant out and creating air pockets. Ran fine with the thermo out, and overheated almost instantly with the thermo in. Compression tests didn't even pick up on it since it was sealed when relatively cool.

[Gnnr]

It may be that you bought a couple of bad ones. Start with that and see how it goes.

Maybe, we'll see when I try a Nismo one.

Your problem is really weird though. How do you know you're overheating? Don't trust the stock temp gauge. Get a real gauge.

I'm using a Greddy MSS with temp signal wire taped into the ECU. Without the thermostat it pretty much stays at 145F.

The car *should* work fine even with a stock temp thermo. My guess is that a) its probably not an OE thermo - the cheap auto parts place ones can be very hit or miss and you can get one that wo't work correctly

They where OEM. Direct from my local Nissan dealer.


b) You are not bleeding the system properly with the thermo installed, and without the thermostat in the car, its bleeding ok and thus the car isn't overheat.

When I try the Nismo thermostat, I'll try your method of bleeding. Thanks.

Do you have to refill coolant often? Blowing coolant into the overflow tank? My guess would be a blown headgasket, or something leaking at temp. Otherwise how is the radiator cap?

I don't remember seeing low coolant in the reserve. I'll monitor the level closely to make sure. It will blow coolant into the reserve after it overheats, but that only happens with the thermostat in. Radiator cap is new, OEM from my local Nissan dealer as well.

I recently had a problem where I blew my headgasket. It was sealed when things weren't expanding too much, but heat and pressure would cause cylinder compression to leak into the coolant system, blowing coolant out and creating air pockets. Ran fine with the thermo out, and overheated almost instantly with the thermo in. Compression tests didn't even pick up on it since it was sealed when relatively cool.

With my luck, I might have weird stuff like that happening. :( Besides the overheating, where there any other signs. Because I can't see anyother signs off a blown headgasket.:confused:


Thanks for the help so far guys.

[AceInHole]

Couple things to look for:

1. overflow tank filling up and not draining (or overflowing)
2. black particles in coolant

[Canaduh]

Just thought i'd throw this out there, but friends car does the exact same thing. He's kinda confused about it as well. We did do the boiling water trick, and sure enough the thermostat opened, He didn't put it in backwards either. Strange too, as his is a 95 as well. Lol. I dunno, siorry i couldn't be much of a help, but your'e not the only one with this problem.

[thejester03]

compression check