Hey family I recently put a gasket kit into my 22re, got it all back together and now I am running into the infamous coolant temp overshoot...It is what everyone describes, as the engine warms up the temps go up to just below the red zone, I'll let off throttle and coast for 15 seconds to a minute then is falls back to where it should be for the rest of the drive. I just put a brand new OEM thermostat in from 22re performance. Before the rebuild she was a champ, never got hot even holding 3k+ rpm for minutes...Ive been holding off putting in red toyota coolant because my buddy runs his race car with straight water and beats it in hillclimbs with no issue. When I filled it after the rebuild I parked it up a incline so the radiator fill was the highest to eliminate air in the system, the engine has 163,000 miles and upon inspection when the engine was apart the waterpump looked healthy. I know I should check correct coolant and radiator cap off the list before posting but I saw posts where people were doing everything right and it still had the overshoot issue I thought I'd probe the forums before jumping on the real fix...One more thing to note, on the left heater hose going to the firewall I have a spliced in filler cap and was wondering if implementing this could help in any way. Thanks !!

 

First VERIFY IF THERE REALLY IS A PROBLEM.
I had an intermittent running hot issue (below the upper white line). I bought a Harbor Freight infrared contact-less thermometer and saw that temp of thermostat housing remained the same (190-degrees +/-) whether gage read hot or normal. Also, the AC kept on running even when gage read hot - there's supposed ot be a cut-off switch for that. Intermittent issue is more likely electrical than of the cooling mechanical system, so I replaced the sender. It had been over a month and I have not seen it run hot. I will still replace the radiator that had seen better days - Stimulus Check, you know
That tap is to back flush the cooling system using a garden hose. Search Prestone Flush and backflush system.
The green coolant had worked on the truck for 30+ years. Don't fix what's not broken.

 

Thanks for the reply! so what you're saying is that the temp sensor was faulty saying the engine was hot when it really was just fine? My issue isn't so intermittent as yours, every time it comes up to temp from cold it just overshoots to just below the red then mellows out, would that still be a faulty reading? I'll try to conjure up a thermometer to test and see if it is really maintaining ~190*

 

Correct
Could be. Some have this issue that was fixed by using two-stage thermostat.
https://www.yotatech.com/forums/f116...l#post52338756

However, need to verify.
Good tool to have. https://www.walmart.com/ip/Handheld-...RoCVsAQAvD_BwE

 

The two-stage thermostat was designed to fix a very specific problem: when the engine is cold and you have the temperature selector lever in the dash on full hot, the heater can cool the coolant down enough that when it re-enters the rest of the cooling system, it will temporarily keep the thermostat closed, because the cooler coolant from the heater ends up near the thermostat. This will cause some of the cooling system (mostly the engine block and the intake where the gauge temperature sensor is) to get momentarily warmer than normal. This is where the "temperature gauge overshoot" problem happens.

Unless you are using the heater on full hot while the engine is still cold, you have a different problem than what the dual-stage thermostat is trying to solve.