Coolant temp changing

[CountyLineGarage]

Hi not sure if this has been addressed but I recently rebuilt my 350 tbi for my truck and have aluminum heads (not sure if it matters). But the coolant temp gauge keeps showing it get cool down to the big line before 210 and heating up to just under 210 it fluctuates up and down quite a bit. I’m leaking a little coolant from one of my lines which I’m planning on addressing but I don’t think that’s it. Does it sound like a stuck thermostat or something else?

 

[RawbDidIt]

Sounds like you've got air in your coolant system. With the truck running and warm fill the surge tank and purge the system by squeezing and releasing the coolant line that goes to the thermostat several times until you notice the level in the surge tank rise and fall with each squeeze and release. Then a few more times for good measure. Take it for a rest drive and see what happens.

Sent from my SM-N976V using Tapatalk

 

[CountyLineGarage]

Sounds like you've got air in your coolant system. With the truck running and warm fill the surge tank and purge the system by squeezing and releasing the coolant line that goes to the thermostat several times until you notice the level in the surge tank rise and fall with each squeeze and release. Then a few more times for good measure. Take it for a rest drive and see what happens.

Sent from my SM-N976V using Tapatalk

Sounds good I’ll give it a try but driving it on the highway it doesn’t seem to surge or at least that I have noticed. Any clue as to what that might be? I don’t think it’s my engine getting too hot at low speeds either cause it goes up and down in park too I’d think if it was the fan or something it would stay hot.

 

[RawbDidIt]

Sounds good I’ll give it a try but driving it on the highway it doesn’t seem to surge or at least that I have noticed. Any clue as to what that might be? I don’t think it’s my engine getting too hot at low speeds either cause it goes up and down in park too I’d think if it was the fan or something it would stay hot.

If there's only a little air in the system, the RPM increase drives the water pump and overcomes the air bubble, as soon as you drop below that RPM range the air bubble comes back and prevents full circulation of the coolant, so the temp rises. A broken thermostat can only fail open or closed, it wouldn't cause fluctuation, it either would take a long time to warm up, or warm up fast and never cool down while running.

Sent from my SM-N976V using Tapatalk

 

[Schurkey]

have aluminum heads (not sure if it matters). But the coolant temp gauge keeps showing it get cool down to the big line before 210 and heating up to just under 210 it fluctuates up and down quite a bit.

The sensor for the gauge goes into the cylinder head near cyl. 1.

Connect a scan tool, look at the Coolant Temperature Sensor readings, which come from the temp sensor by the thermostat.

Find out if the engine coolant temperature is REALLY changing, or if it's a gauge/gauge sensor/gauge wire harness problem.

 

[thinger2]

Air, bleed it a few times

 

[Erik the Awful]

Coolant-specific funnel for bleeding air out. One of the best tools I ever invested in.
https://www.amazon.com/Lisle-24680-Spill-Free-Funnel/dp/B00A6AS6LY