The Stovebolt Site Forums The Shop Area Engine Shop Thermostat temps

I recently replaces my 216 for a 62 235 in my 49 pickup. When I start my engine and watch the temp gauge start to rise as the engine warms up, the gauge will run up to around 200 deg and then it will drop back down an stay at around 190 from that point on. I put a 180 deg thermostat in engine and was just wondering if I need to go to a cooler stat to keep it from running up to 200. I have put an electric fan in front of radiator an it seems to be working ok but was kind of concerned about the 200 deg. Any advice on this subject would helpful, thanks guys.

I think that overshoot is quite normal. However, I would be wondering about why it runs at 190 and not 180. I tend to be a worrier!

I would find what the actual temp is with a laser thermometer before doing any thing. It could be gauge variance. Truck gauges aren't exactly scientific instruments.

That being said, getting up to 200 before the thermostat opens won't hurt the engine. I'm sure it gets hotter than that from residual heat after shut down.

Is your heater valve closed? With no by-pass this initial spike then stabilization at a lower temp. would be expected.

that would be just fine in any circumstance, you don't need to use an additional fan, and on that note, a fan in front of the radiator will actually hinder airflow at highway speeds. possibly causing more problems. If you need an extra fan, you have something wrong, these will run just fine the way they came from the factory, in fact in California Bills books, he says that is the one thing that should cause no issues even with substantial modifications. I ran a 195°thermostat for 25 years with no issues.

Overshoot is normal for thermostats. How much will depend on the quality and design of the thermostat (example: air bleed holes). As far as temperature concerns, water not under pressure will generally boil at 212F, 50/50 antifreeze at 235F, and antifreeze at 15 psi pressure (radiator cap pressure) will take 265F. Higher temps may help efficiency, but decrease power slightly.

A thermostat can usually be checked by placing it submerged in a pan of water on the stove. Use a thermometer. When the stat begins to open you will see air bubbles released. I have used this in the past to choose between different thermostats and rejected those that took too long to open.

The reason for the fan in front of the radiator is because I had to put a short shaft water pump in because of the engine change and I had no room for the original fan, so I have no fan on the engine. I have later found out that I can order a different fan that will fit between radiator and engine so eventually I will discontinue the electric fan an run just the engine fan.

You are right, after shutdown the temp runs up to 210-215 then gradually starts dropping. I have ordered a fan that will fit between the engine and radiator and at that point I will discontinue the electric fan. I just wanted to be driving the truck until the new fan gets in and didn't want to mess anything up in the meantime. Thanks for the information.