SBC going through thermostats...??

[Green79Scottsdale]

First off, not a square, or my vehicle for that matter. Just trying to help one of the "kids" at work.

Built 350 in a 1979 Camaro. Kid says he has gone through about 6 or 7 thermostats in the last couple of years. He has been fighting an overheating problem ever since he got the car. He has replaced the radiator, hoses, and water pump within the last couple of summers. He noted that whenever he replaces the thermostat the overheating issue goes away for about 3-4 weeks. Then the car goes back to overheating. Replace thermostat, problem goes away again.

Anyone ever hear of this? The only thing I could think of off the top of my head was maybe a wrong rotation water pump. He says it's just a standard pump, nothing high perf. Also thought maybe a head gasket on backwards or upside down. Any ideas from you guys?

Details are a bit sketchy on this car to me personally. Can get more details tomorrow. Thanks in advance for any help.

 

[chengny]

Automotive thermostats are simple, effective and above all - reliable.

For a person to find even one t-stat that fails to open (usually they fail to close if anything) is rare. To get 6 -7 bad out of the box in a row...I don't know, maybe he should call the folks at Guinness.

Not much to go on but, I would have to think that just the process of changing the t-stat is what temporarily solves the issue. Has the kid attempted to just pull and then re-install either the same t-stat (or one of the many dead soldiers)?

Has an autopsy ever been performed on one of the "failed" thermostats (i.e. drop it in a pot of boiling water and see if it opens)?

I would look at whether there is any air/combustion gas entrained in the coolant.

Some t-stats have a small by-pass to help bleed off any air that gets trapped under the disc but that is really only for initial purging. Once any air left over from the installation goes past the stat it migrates to the radiator and then out to the expansion tank.


We have to assume that the thermostat is being installed right-side up (because it seems to function for a few weeks).

Other than a small head gasket leak, which would allow combustion gasses to slowly build up within the coolant, I got nothing really.

This is a good one - beyond me. But don't worry, I'm sure it won't be long before you hear from the "big guns".

 

[Green79Scottsdale]

Thanks for your reply chengny.

I fully agree with the simple effective and reliable part. Put a new one in my Monte about 15 years ago and still works perfect to this day.

I didn't think about the boiling water test. I will pass that along. I will also tell him to just pull it the stat out and put it right back in to see if it is the process or the part.

I also thought about the pressure build part also. I do not know if he has an expansion tank or not. That's another thing to discuss with him. I had suggested to him that there could be an air bubble somewhere in the system, but he insists there isn't.

For some reason he has been suggesting he might change the head gaskets, even though he has no real good reason as to why. If he does have a small leak or one is installed wrong that would relieve undue pressure in the system.

Alright, thanks for the discussion. I know this is not the best way to go about things, but it makes me look really smart to him!

 

[chengny]

As a test, have him run the motor without any t-stat at all for a while.

The engine will initially run cooler than normal. But, if he has H/G issues, he'll eventually start running hot (due to vapor pockets in the coolant). This happens even with no thermostat installed.

However, if the engine runs cool (without a t-stat) and stays that way for an extended period... I have no idea.

 

[MrMarty51]

Napa sells a "Premium" line of thermostats, maby have Him try one of those.
They are built a bit heavier than a over the counter run of the mill units.

 

[Green79Scottsdale]

He has tried them. He said he thought he has the last one he took out still, so I told him to put it in boiling water and see if it opens. I also told him next time to take out the thermostat and put it right back in. That would tell if it is the part or the process. I am going with an air pocket in his system. How it is getting there is the mystery. I like chengny's recommendation of going t-stat-less and see what happens.

 

[MrMarty51]

He has tried them. He said he thought he has the last one he took out still, so I told him to put it in boiling water and see if it opens. I also told him next time to take out the thermostat and put it right back in. That would tell if it is the part or the process. I am going with an air pocket in his system. How it is getting there is the mystery. I like chengny's recommendation of going t-stat-less and see what happens.

YUP, Me too.

 

[austinado16]

Rule No. 1: Always confirm the customer's complaint

So this case; a) What was done to confirm the engine was overheating? b) What's been done to confirm the thermostats are all bad?

Testing coolant temp with a calibrated thermometer is the best way to know if an engine is hot. An infrared temp gun can also be handy for this.

If the head gasket(s) are blown, the easy test is to take the vehicle to a shop that has an exhaust gas sniffer/analyzer, or an emissions test machine. "Sniff" the steam at the top of the radiator tank with the engine running. If the machine picks up any CO or HC's, there is a failed headgasket that is allowing combustion pressure/air/heat/gasses to be pumped into the cooling system.

As for the t-stats, I think they can be damaged by the boiling water. They'll open long before that, so no need to cook them too much. I like the Mr. Gasket T-stats.

 

[Driver4r]

Rule No. 1: Always confirm the customer's complaint

So this case; a) What was done to confirm the engine was overheating? b) What's been done to confirm the thermostats are all bad?

Testing coolant temp with a calibrated thermometer is the best way to know if an engine is hot. An infrared temp gun can also be handy for this.

If the head gasket(s) are blown, the easy test is to take the vehicle to a shop that has an exhaust gas sniffer/analyzer, or an emissions test machine. "Sniff" the steam at the top of the radiator tank with the engine running. If the machine picks up any CO or HC's, there is a failed headgasket that is allowing combustion pressure/air/heat/gasses to be pumped into the cooling system.

As for the t-stats, I think they can be damaged by the boiling water. They'll open long before that, so no need to cook them too much. I like the Mr. Gasket T-stats.

Never damamged a T-stat by testing it that way.