3.4 running hot, running out of ideas - S-10 Forum
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post #1 of 2 Old 03-24-2019, 10:00 PM Thread Starter
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3.4 running hot, running out of ideas

Well it seems nothing has been going easy with this swap lately.

What I've done so far,

New rad (hit a deer)
Brand new clutch for the fan
New rad cap
New AC Delco 192* F thermostat

My truck runs hot, like 200-230*f with the 192* thermostat. I've tried this ac delco thermostat and a stant 195* just to verify the thermostat is not the issue. With both of them the truck is constantly cycling between 200-220.

I've tried pulling the thermostat out completely and running it fully open to ensure the water pump is flowing coolant and sure enough there is a constant steady stream coming out of the rad in this situation and the truck runs super cold, barely reads on the gauge.

I've tested all 3 thermostats in boiling water and all open at the right temp, and fully open within 10-15 degrees of their rating.

I've made sure the lower rad hose wasn't collapsing cutting off flow. I've burped the air very thoroughly to ensure it wasn't air locked. The engine was just rebuilt 10k miles ago and I'm not getting any air bubbles in the rad indicating a bad head gasket. I have no leaks anywhere, holds pressure well when tested.

Here's the kicker, when I put a 180*f thermostat in it, it runs pretty well perfect at that temp, it may cycle up to 190ish under heavy load but quickly cools back down to 180.

I have yet to swap out the temp sending unit, although I don't believe it's the issue because it seems to be reading correct values when swapping the thermostats for one another.

Is it possible the water pump (50k original miles on it) would function properly at 180*f but then start to free wheel not move enough water at 195*? It boggles my mind that the system will cool properly at 180 but not at 192?

Any ideas or suggestions on what to try next would be really appreciated. I would love for this 3.4 to just run at a constant 192*

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post #2 of 2 Old 03-28-2019, 12:15 AM
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I would find out what degree thermostat goes in you engine and what temperature it should run at. Put in the right thermostat and see what the temperature it gives you. If its still overheating, I think a safe bet is the waterpump.

It could be the temperature sending unit. I would try whatever’s most likely to be bad first rather than replace everything so you can know what was wrong.

Other than that, make sure there’s no coolant in the oil. That’s a gasket problem, I think

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