Cooling System Confusion

[ForeverDrivin]

Hello again everybody, I want opinions.

I have a 1997 Mustang with a SC coyote swap, but recently tore the motor down a little and put it all back together. Here's my issue.

Once it gets up to temp and I'm driving around, the computer monitored coolant temp stays perfect. Right where you want it around 190-200.

However, my mechanical coolant sensor starts reading up into the 220-230 range, fluctuates a bit. It is located on the bottom driver side of the block, where the block heater normally is.

I immediately thought headgasket like anyone, as I did not have the block decked while the heads were off, only scrapped old gasket off (the heads were cleaned by a shop). But, there are no bubbles in the coolant on startup and it passed a CO2 tester.

The gauge is a glowshift setup, I'm imagining the sensor might've just ate it while the car was apart and it was exposed to air, but I can't tell. I've heard mixed things about GS and my gauges worked well until this little issue.

Its funny, I bought the mechanical gauge because I didn't trust the head sensor and now I don't trust the mechanical sensor! Lol.

Any help is appreciated,
Blake Hammond

Sent from my SM-S906U using the svtperformance.com mobile app

 

[biminiLX]

First why did you tear it down to begin with?
You can test the mechanical gauge off the car but in this case is the car showing any signs of overheating or running poorly?
I’m guessing bad sensor.
-J

 

[ForeverDrivin]

First why did you tear it down to begin with?
You can test the mechanical gauge off the car but in this case is the car showing any signs of overheating or running poorly?
I’m guessing bad sensor.
-J

I didn't tear it down for any big reason related to the motor, it didn't overheat before or anything.

I tore it out to do a TKX swap, clutch, and motor refresh. Head journals needed polishing and valves were lapped, so new valves and redone seats, plus some fun MMR stuff up top.

I'm thinking a bad sensor too, but I also don't know exactly what the shop did with my CHT sensor. If they took it out, Ford says I need to replace it and I can't trust what the computer is saying. Maybe the mech gauge is correct, it matched the CHT pretty well before the project, and I still have an overheating issue.

Can't be sure but I'll check with the shop tomorrow, and order a replacement sensor from GlowShift. $30 try-it fee isn't bad, wish I could test it first but I work out of a unit, can't get hot water out there for testing. Get back with that at the end of the week.

-Blake