My car overheated

[Guest Z-rific]

Not my Z, but my '95 Talon.

 

I had noticed it running warm for a few days. One day it got real high, but it seemed to settle down. Then my girlfriend took it to work and it overheated. Not too bad, thank goodness.

 

Anyway, I filled it with 50/50 water and antifreeze. Drove it home and the temps rose again. Let it cool. Had to add more water. Took it around the block and temps rose slower, but still too high.

 

Nothing is leaking and both the electric fans are running. Not sure why it's still running hot. The water level didn't drop the second time.

 

I priced a new thermostat for about $10. It's a 180 degree. I'm hoping it's stuck open and the water isn't sitting in the radiator long enough to cool.

 

I got to fix this by Xmas, as I need to take it to my GF's folks house about an hour away.

 

Anybody have any other suggestions?

[Synlubes]

Hey,

Don`t ck Change the thermostat!

Ck inside radiator for biuldup/blockage!(ck for anything blocking air flow thru radiator)

If you see anything inside the radiator other than clean open rows, flush cooling system and then after the flush run clean water thru to clean the flush agent out!

 

NOTE: A cly head retorque would not be a bad idea!

[Guest zfan]

Check for air pockets, don't want air in there. My friend drilled 1/4" holes in his thermostat(180) degree housing and it cools like a charm.

 

Mike

[Guest greimann]

Originally posted by Z-rific:

..... I'm hoping it's stuck open and the water isn't sitting in the radiator long enough to cool.

 

...

My "Urban Myth" alert went off when I read this. This is a false concept that is proliferating throughout the automotive boards, and I am compelled to squash this whenever I see it.

 

A thermostat has two functions. To maintain a minimum temperature in a motor so it doesn't run too cool, and to act as a pressure metering orifice to help the water pump build up pressure in the block. People falsely concluded that when they removed the thermostat and then had problems with coolant coming out of the overflow, that it was due to overheating. What was really happening is since the pressure metering orifice (thermostat) was removed, the water pump pressure backed up against the radiator cap, which is a pressure relief valve. The water was not any hotter, it was all caused by a misplaced pressure differential.

[Guest Z-rific]

Okeeeedokeeee,

 

Can you put that in layman's terms for me?

 

So you're saying that the thermostat does NOT close to allow water to sit in the radiator to get cool air and cool down, but to build up pressure to insure water flows strong enough through the block?

 

I've replaced the thermostat and am in the process of flushing the system. When I warmer 'er up last time, the temp gauge looked much more stable.

 

I'll post results in a few hours.

[Guest Z-rific]

Thanks for the explanation. What would be the advantage of using a 200 degree therm. over a 160?

 

By the way, either the thermostat was bad or the radiator just needed a severe flushing.

 

I replaced the thermostat, flushed the sytem with a cleanser, then completely flushed it where pure water was going in up top and clear out bottom. Then I did a 50/50 water/antifreeze mix and test drove it for about 45 mins. The temperature gauge stayed below half the whole time.

[Guest greimann]

Provided that the engine runs fine with either a 160 or 200 degree thermostat, the higher temperature allows the motor to be more efficient with a given volume of fuel. Most of the heat of combustion is expelled as hot exhaust gas, some is absorbed by the cooling system and a small fraction (about 25%) is turned into work to turn the crankshaft. If you can divert some of the heat that would be normally absorbed into the cooling system and turn it into work, then you have a more efficient motor. We are only takling about fractions of a percentage, so the gains are not great.

 

There is, however, other things to consider may make the motor more efficient by running it cooler. If you have a high compression motor that needs to run cool or it will detonate on the crappy 91 octane California gasoline (like me), then running a 160 degree thermostat allows me to run more timing wihout detonation, which is better for power than a hot motor.

 

If you have an EFI motor and are running a 160 degree thermostat, the computer may never come out of cold start mode and run extremely rich, which is no good for power or economy.

[Guest greimann]

The thermostat only closes when the water temperature is below it's opening point, such as when you first start up from dead cold. Its function is to establish a minimum temperature so the engine doesn't run too cool. The upper limit of engine temperature is established by the effeciency of the cooling system. During normal operation, the thermostat is wide open all the time so the water flow is at it's maximum for the best cooling. When it is cold outside, and the cooling system has no problem dealing with engine heat, the thermostat may partially close and limit coolant flow to prevent the engine from overcooling.

 

The pressure limiting function is the reason why one should never remove a thermostat.

[Mudge]

I can't comment on the closed loop operations of the ZX/ZXT ECU, but the OBD I stuff is closed loop by about 140ºF (60-300 seconds typically), although I can look in my logs for sure if someone really cares to know the exact answer. There ie also a "minimum temp closed loop cold MAT, which I've never seen affect my CA car. The 160º thermo isn't fully open until nearly 180º (for the one that I tested anyway).

 

I never use a 50/50 mix, but it depends on where you live. If you see tons of very hot/cold weather, then maybe thats appropriate. I use closer to 90/10, with using distilled water ONLY. If the coolant sensor doesn't rely on conductivity and only level, then I would not use coolant at all, I will probably do that for the Z before I take it out on the track.