The Stovebolt Site Forums The Shop Area Engine Shop 235 Chevy 180 Thermostat Slow to open (Temp shoots past 220)

Hey guys,


I recently installed a heater in my 53 Chevy Pick up. I drained the radiator, and installed a new 180 deg thermostat.

Since then, the org. gauge shot up over 220, and eventually broke the gauge. I installed a temporary gauge and see that when I first run the engine it shoots up past 240 degs and then will shoot back down to right around 180. While driving it will go up to about 220 before the thermostat opens up.

I first thought it might be an air pocket, but I did burp the system ( at least I thought I did.. by leaving the cap off until I got some fluid coming out of the top radiator then placed the cap back on). But the temp gauge still shoots before the Thermostat opens up.

Also, the thermostat that I purchased already had a pre-drilled hole in it (with a little brass jiggly thing in it), so I thought that hole would be enough. Perhaps another hole?

Anyone have thoughts about what would be causing the thermostat to not open up until the temp gets much hotter then it should?

-James

Sounds like a faulty thermostat to me. If you have a thermometer you can put it in a pan of water on the stove and monitor at what temp it starts to open.

You may already know this, but a thermostat does not establish the top range of temperature your engine will run at...it establishes the lowest temp your engine will run at. I find that confuses some folks. I'd buy a 160 degree thermostat and go with it. If you are tempted to purchase one of the thermostats sold under the name "Fail Safe" please consider another brand. If your engine ever overheats---even once, that thermostat is forever disabled and left in the open position.

If you put a 180 degree thermostat in a pan of hot water with a candy thermometer, you'll see it starts to open at 180...just a crack and it may even be hard to see it is doing anything. It won't get fully open until around 220~230 and that's what yours is doing. I don't see any reason to run a 235 at 200 degrees or more and neither did the guys who designed it. Good luck!

Side note: a year ago I tested 4 different makes of thermostats (all 160 degrees) to see if they were all about the same. No dice. Two of them didn't begin opening until 180 so I assume they were either defective or marked incorrectly in the country of their manufacture (which was not the USA).

I have a 180 deg thermostat and it works just fine. I did have a problem with erratic water temps earlier this year and it had to do with heater hose routing. I had to add a bypass.

Your problem started after you installed a heater (and new thermostat) - did you replace the old heater or is this a completely new install?

Well technically yes the problem did start after I installed a new heater (never had one before). However, that is when I found out my father in law who owned the truck decided it was best to remove the Thermostat and hadn't had one in the truck for years.
When I was installing the heater I purchased a 180 deg thermostat, thinking I would swamp out the 160 deg one, but when I opened up the housing, there was no thermostat.
Thats when he mentioned he would always have problems with the thermostat being stuck closed. So I may have stumbled on a pre-existing issue that he never solved and left it to me to stumble across.

I would put the heater hose plumbing back to the way it was before you installed the heater and test to see how it runs. The idea is to only change one thing at a time to make it easier to diagnose the problem. If it still overheats, you have narrowed it down to the thermostat area and you can do the cook it on the stove test as Jon suggested. If it doesn't overheat, you know the thermostat is ok and something is wrong with the heater installation.

You have a defective therm. or it is in up-side down. About 1/3 of the new thermostats we get are defective. Most therms go up a little higher before they open & then go back to the running temp. Yours is way to high.
George

I just put in a high flow 180 thermostat in my 54. It did not get warm enough in the winter with a 160 but I drove it today 33 degrees with the 180 and it got toasty in the truck. It says offroad and racing only. Got it at Auto Zone.