Automobile (Firebird 400) Thermostat

[Richard]

Wife's cousin next door has a Firebird convertible. Not sure of the year... I'm guessing anywhere from 1969-1971. Has a 400 engine per emblem on the hood.

He doesn't drive it as he says it has an over-heating problem and has since he obtained it.

"Have you checked/replaced the pump?" Yep
"Have you checked/replaced the thermostat?" Yep
"Have you had the radiator looked at?" Yep, it's either new or cleaned/reinstalled

Says all the above were replaced and it still over-heats. He then went on to say (if I recall correctly) that the prior owner removed the stock fan blades and replaced them with an electric fan. So now, it's either on full time or (I suppose) not working or, working intermittently.

That said, I'm not 100% sure how accurate the fan part is. I never looked at the fan.

My primary question is, testing the thermostat. Are they stamped with what temp they open? I recall there is a range they can operate.... if not stamped on unit, how can one ascertain what it's rated at?

If it is this electric fan (I have NO experience with them) what is it tied to temp wise, to tell it when to kick in/out?

I'm certainly not a certified mechanic but, if I am not a certified mechanic.... then his rating would be that he's not a certified observer lol. What I mean to say there is my background is a LOT more mechcnially inclined than his... heck, I gave him a strobe timing light and a tach/Dwell meter because I'll never likely need them again. He said he had no clue how to use either one.

So, I'd like to help him. I didn't know about it having an electric fan. Seems to me the easy answer is to just go back to the fan with belt....

No real question.... just trying to see with the above, what other thoughts might be on where to look for the issue. The car is just sitting under a tarp... unused.... and I'm of the belief that cars do not like to be unused.

 

[Richard]

Heck, I should ask about buying it off of him....

 

[ericm979]

Thermostat should open between 160 and 195. Most are 180. if the water's boiling and it's still not open, it's bad.

As cheap as they are it's often more effective to replace them than to bother testing them.

The 400 was a pretty durable engine. The overheating could be from warped heads if it was run on low coolant. But if your friend is not all that mechanical, his checks might have missed something.

 

[RustyA]

1. Pressure test cooling system to make sure it holds 16-18 psi overnight. That should help eliminate possible head gasket issues.
2. Make sure radiator cap is in good condition to maintain the rated 16-18 psi during operation.
3. Use an infrared non contact thermometer to take temp readings at various locations on engine, thermostat housing and radiator to try to narrow down if it is really overheating or gauge just reads high.
4. Determine how the added electric cooling fan is controlled. It should be coming on around 200-210 degrees if thermostat is 180-195.

 

[jaxs]

Heck, I should ask about buying it off of him....

Be much simpler letting me come pick it up and you wouldn't need to worry with it.
Is it steaming or just indicating overheat on dash gauge? If the later I'd install temporary guage and/or use laser thermometer to confirm temperatures.
T-stats are usually stamped w temp but even the highest rated wouldn't cause sever overheating. Stuck maybe,how to check,bring pot of water to boil and lay stat in it. If stat doesn't open it's defective. If stat opens at 212F but stamped 180,remove stat,add and swirl cool water until water in pan is 185f,stat should open when dropped in 185f water. If in doupt,since stat is already out replace it.
Secound (if not first) test I do is for blown gasket/cracked block/head. Parts house sells chemical that changes color of coolant in presence of exhaust gas.
Electric fan is a good addition to older engines to keep them cool at idle and traffic. Regardless whether electric or origional,fan needs enough and right size blades to cool. Make sure shroud is installed and blades are positioned correct inside shroud. For troubleshooting a clamshell from a gas furnace can be positioned on radiator.
Rare but pump impelleres come loose and slow or stop circulation.
Altered engines always create additional heat so oversize radiator,improved pump and other additions insure the investment.
Eyeballing through fill neck is inexact in judging cleanness of radiator. Flues don't have to become blocked or partally blocked,a coating can slow heat transfer so I have radiator cleaned when engine is rebuilt.replaced or modified.
A car this vintage is often modded for more power,larger engine dropped in while origional radiator retained. All the above might apply so every little bit amounts up.

 

[scootr]

Me 2. I can fix this problem for him. That 400 Firebird is on my bucket list.

 

[ovrszd]

The most worrisome thing you said was that it had this overheating problem when he bought it.

Since he has no mechanical knowledge, I'm guessing he was told it had a good water pump, good thermostat, good radiator.

If the thermostat is not opening, the engine will get hot and the top radiator hose and/or top of radiator will be cool. The thermostat on that engine is very easy to remove. Put it in a pan of water on the cookstove with a candy thermometer in the water. Turn on the heat and observe the thermostat. When it opens, read the thermometer. If the water boils and it doesn't open, it's defective.

If the thermostat is opening, with engine running, radiator cap off, you will see antifreeze circulating in the radiator. If you don't see water circulating the water pump isn't working. Another quick test of the pump. Start the engine, turn on the interior heater, as the engine warms the heater hoses will get hot. They'll do that before the thermostat opens. If not, the pump isn't working.

Electric fan test should be very easy. Start the engine, engine gets hot and the fan isn't running, defective fan or electrical circuit powering it. Or another simple test is to hot wire the fan. Don't even need to start the engine. Run a hot wire from the battery to the positive terminal on the fan, it should come on. If the fan is on a thermostat it might be defective. If it's wired direct to key, key on/fan on and it isn't running, again defective fan. Hard to say on this situation without standing there. But within 3 minutes max I'd know if the fan is functional.

So, if the thermostat is working, the pump is working, the fan is working, the problem gets deeper. Now we are getting into the area I raised concern about in the beginning. The seller got rid of a problem that he didn't want to spend the money to fix.

Let us know what you find out.

 

[ssgp2]

Is the fan shroud still in place? In my younger years, I built and raced Pontiacs (hotrods). While I loved the Ponys, once they were bored, as mine were, they did run a little hotter, more than Chevy or Ford. Any how, when I would test run a new engine, I found that without the shroud, they got real hot within a few minutes. They would also overheat without the t-stat. My 455 SD at .060 over did better with a 195 degree than anything else. Put the mechanical belt drive fan back on with the shroud and use a Flex fan and see what happens. Assuming the block and head ports are clear with the proper head gaskets properly installed, you should be good

 

[Boss 302]

Absolutely, make sure the fan shroud is in place. That's a biggie.

 

[MossRoad]

A thermostat for a 70 pontiac firebird with 400 engine is $8 (eight dollars) at Autozone.