Coolant temp fluctuating up and down

[El Tigre]

I give up... Keep using the totally wrong thermostats....
Wondering why you have cooling system troubles.

 

[Courchained]

I give up... Keep using the totally wrong thermostats....
Wondering why you have cooling system troubles.

What tstat do you recommend?

 

[Schurkey]

The one with the extra spring and plate, to close-off the passage at the bottom of the thermostat pocket.

It's only been pictured two or three times in this thread, one of which you responded to.

All thermostats except this last one pictured are WRONG....

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Is this the delco?

Doesn't matter what BRAND it is, (Delco, Stant, Robertshaw, MotoRad, something else) what matters is the bottom spring and plate.

Cadillac, Ford Cleveland, some Chevy V-6s, and various other vehicles use a similar if not exact lower plate. The thermostat part numbers may/may not be different, but the concept is the same. Be sure you have the CORRECT thermostat for YOUR VEHICLE.

 

[JeremyNH]

Stock tstats are 195F. Sounds like you have a 180F. Maybe right for the L31, maybe not, but the setpoint temperature is non-stock and the behavior non-stock by consequence. The lower T ratings are for boosted and "performance" builds. You have a stock motor so use a stock tstat. Go to RockAuto and buy the ACDelco OE style and get OE behavior. Or don't and don't. Your call.

 

[El Tigre]

180 is fine ,and so is the 160 version. though it's more popular on the LT1's as they tend to run 10-15 hotter than the stat due to being located where cooler coolant enters engine from radiator. Vortec Thermostats are located where hot coolant goes to radiator as SBC have always done. 195 stat guarantees coolant will be no cooler than that. Hard on underhood plastic ,and rubber.

 

[JeremyNH]

Lower temp ratings will work but he will see more temperature swing because the tstat is fully open at a lower temperature. With a 195F it starts to open at 195 and is fully open at 205-210. Cools down to 195, tstat closes, begins to heat up again, tstat starts to open, and eventually settles at a point where it is partly open to throttle the right amount of coolant to the radiator to maintain temperature. At 180F the swing will be more. We know that at full flow the engine will cool because the different tstat settings don't change the flow rate when fully open only the temperature at which fully open. But fully open will cool down the engine at all loads and ambient temperature since that is what it is designed for. He is complaining of temperature swing and that is due to having a tstat setting below the stock 195F. And it isn't hard on anything since that is what the motor is designed for else it wouldn't be stock. A lower setting subjects to thermal cycling which is a different kind of stress.

 

[Courchained]

Stock tstats are 195F. Sounds like you have a 180F. Maybe right for the L31, maybe not, but the setpoint temperature is non-stock and the behavior non-stock by consequence. The lower T ratings are for boosted and "performance" builds. You have a stock motor so use a stock tstat. Go to RockAuto and buy the ACDelco OE style and get OE behavior. Or don't and don't. Your call.

The truck currently has the ac delco tstat from rock auto and looks just like the one pictured with the lower valve. The fluctuating is still present. And it is a 195 Stat. I recently had a start 195 in it with that lower valve and that one had the fluctuation as well. The stand I tested and it opened at 198 and closed at 184 so that is bad. My guess is the delco is also bad...

 

[Aperrado]

Try to flush the cooling system and then refill it, when you make it,start the truck and put the heater on hig maybe it can work for you that was my problem on my gmc dierra 98 Now its working good, the person that tell me to do that, told me that it has air on the cooling system. Try!

 

[El Tigre]

Probably does have air in system. Heater on high does nothing as these truck do not have heater control valves. Letting air out by disconnecting heater hose from intake manifold can help a lot. Installed a bleeder screw there for that purpose.

 

[Courchained]

Probably does have air in system. Heater on high does nothing as these truck do not have heater control valves. Letting air out by disconnecting heater hose from intake manifold can help a lot. Installed a bleeder screw there for that purpose.

I'll try this out. Did you just splice the line there for the bleeder valve then?