correct thermostat and running temp ?

[Ron Hambrecht]

After having a head repaired from a crack in the valve seat, my C2 360 hp fuelie is running better and stronger than ever, however... it is suddenly running at 210 degrees, with up to 215 when stopped longer than a few minutes.

what is proper operating temp for this engine ?

what is correct thermostat ?

[Michael H.]

Re: correct thermostat and running temp ?

Ron,

Originally, these cars came equipped with a 180 deg thermostat and when all is well, they will run at 180. There are a number of things that can and will cause the temp to run higher than this, especially if your radiator is old and loosing efficiency. (there are a number of receint posts on this issue and the fix is, indeed, the Dewitt replacement unit)

If the problem started at the same time the cyl head problem was repaired, I would have to guess that something in the mix has changed. If the engine is making a lot more power since the repair, it would also be making more heat and this could be responsible for the added temp. Also, is it possible that you now have a 195 deg thermostat in the car?

My 63 FI car always ran at around 180 deg for years but in the last 10 years, the temp started climbing to 200. It has the original radiator so I know it's time to make the call to Dewitts.

[Joe L.]

Re: correct thermostat and running temp ?

Ron-----

The correct thermostat for your car is a 180 degree unit. The current Delco part number for said unit is GM #10207381. I don't recommend that unit, though. Instead, use Robertshaw #330-180. This is the best thermostat for your application.

You could use a lower range thermostat, but I don't recommend that, either. For one thing, a thermostat only controls the LOWEST temerature that an engine will run at (after warming up, of course). It absolutely has no effect on the HIGHEST temperature that an engine will operate it. That is controlled by "other factors" and there are MANY that are involved including, but not limited to, condition of cooling passages, condition of waterpump, condition of radiator, condition of fan clutch, condition of fan shroud seals and/or radiator seals, initial timing, condition of vacuum advance control, coolant concentration and ambient temperature. There are others, too.

The reason that it doesn't usually pay to go with a lower range thermostat is that the upper temperature is not a function of the thermostat, anyway, and the cooling system probably isn't capable of maintaining a 160 or 170 degree maximum temperature. So, there's no advantage to trying to establish your "control point" at a temperature that your system isn't capable of maintaining anyway. In fact, there's a disadvantage to doing this since it will "encourage" wider temperature SWINGS which is not a good thing, at all.

So, the long-and-the-short of it is use the Robertshaw 330-180. That will do the best for you as far as the thermostat goes.

Under certain operating conditions, I would not consider the 210-215 range to be too hot, but it's certainly on the edge of it. If the condition is mostly noted at idle, then I'd say your fan clutch is suspect. That's the most common cause of overheating at idle. There's really no way to effectively test these things. If it's old, replace it. GM #3916141 is the way to go.

If the higher temperatures are noted at both cruise and idle, then I'd say that a marginal radiator is the most likely culprit. These things get old and clogged. If you happen to have a copper/brass replacement for the original aluminum unit, that could be a BIG part of the problem. The copper/brass replacements do not have the cooling capacity of the original style aluminum units. There's really no way that a copper/brass radiator can be made in the configuration of the original aluminum unit (for direct fit purposes) and have the same cooling capacity as the original aluminum construction. Under "normal" conditions they usually cool ok but when "stressed" (such as in high ambient temp conditions or prolonged hi load operation) they will be very marginal, at best. Use a DeWitts reproduction of the GM #3155316. It's the ONLY way to go if you need a radiator for your application.

[Larry L.]

Re: correct thermostat and running temp ?

If you are using indicated temperature - don't spend another dime until you get a accurate thermometer - an refrigeration thermometer or thermocouple and meter. Tape it to the intake at about the location of your sensor that is screwed into the manifold. Check this temperature after a drive to get up to temperature and check the temperature in the coolant recovery tank. Then you know the correct temperature. Then plan a fix. This will save you a lot of money.

Larry Linder

[Mike McKown]

Re: correct thermostat and running temp ?

If you were okay before this repair and immediately after the repair you were overheating, the first thing I would suspect is you didn't purge all the air out of your cooling system when you re-filled it. The second thing that comes to mind is that you are losing combustion pressure through your repaired valve seat and it is putting air in the cooling system.

[Richard D.]

Re: correct thermostat and running temp ?

Guys -

I had some difficulty finding a Robershaw thermostat for my car, but discovered that Mr. Gasket makes the same design (high flow,and fails in "open" position if indeed it does fail) under license.

Got it at my local speedshop for about 7 bucks.

Thought you might find this useful.

Regards,

Rich

[Joe L.]

Re: correct thermostat and running temp ?

Rich-----

It's very likely a Robertshaw that's packaged by Mr. Gasket and sold under their brand name.

These days, the Robertshaw brand is sold under the Prestone brand name. Robertshaw is part of Cooper Industries and, apparently, has licensed the Prestone name from Honeywell (they now own Prestone). In fact, I just purchased one this morning (a 330-180) for the "ZL" project. I got it at Kragen which in other parts of the country is known by other names.