Mechanical temp gauge False overheating

[GmTard89]

So my 94 k2500 5.7 i bought last year came with the coolant temp gauge deleted and a mechanical gauge mounted on the A pillar. After new motor installed and first startup and test it was shut down multiple times for overheating 230 240 250ish . Turned out it's not over heating it will go from cold to 260 + rolls over to the gauge's 100 mark then thermostat opens and it drops to 195 again . infrared shows normal intake and fluid temps so i believe gauge mounted on the drivers side head just gets hot in the coolant passage before tstat opens is this normal for other mechanical temp gauges or the head to get that warm before t stat opens ?

 

[Schurkey]

I've heard for many years that temp sensors mounted in the head will run 10--20 degrees F. higher than temp sensors mounted in the intake manifold cooant crossover passage.

Kinda guessing that your mechanical temp gauge is picking up even more exhaust heat than an electric sending unit would.

 

[GmTard89]

it is exposed a little more than a stocker and I have long tube headers . little more concerned about the high temp before t state opens and it goes to 195 when open but yeah heat creep probably

 

[PlayingWithTBI]

After new motor installed and first startup and test it was shut down multiple times for overheating 230 240 250ish . Turned out it's not over heating it will go from cold to 260 + rolls over to the gauge's 100 mark then thermostat opens and it drops to 195 again

Tell us some more about your new motor. Is it a TBI block with TBI heads, or is it a TBI block with Vortec style heads, or is it a Vortec block with TBI heads?

 

[GmTard89]

Tell us some more about your new motor. Is it a TBI block with TBI heads, or is it a TBI block with Vortec style heads, or is it a Vortec block with TBI heads?

Stock tbi 350 tbi heads rebuild

 

[PlayingWithTBI]

Stock tbi 350 tbi heads rebuild

It sounds like you're not getting enough bypass when the T-Stat is closed. The TBI water pump and block has that bypass. Is you heater core still hooked up and free flowing?

 

[GmTard89]

It sounds like you're not getting enough bypass when the T-Stat is closed. The TBI water pump and block has that bypass. Is you heater core still hooked up and free flowing?

Hooked up free flowing idk I might bypass it to test

 

[Schurkey]

"I" would grab two feet of aluminum foil, fold it over a several times, and form a multi-layer aluminum cylinder three+ inches high and about an inch-and-a-half in diameter, a temporary heat-shield around the outside of the temperature probe and adapter that fits all the way down to that cylinder head, with an insulating air-gap to the capillary tube if not to the entire housing of the sensing bulb.

If the temp gauge doesn't go up as high as it used to, and the aftermarket gauge tracks the temperature somewhat closely to the ECM sensor in the manifold, you know the sensing bulb and capillary tube is picking up radiant heat from the exhaust, and it has little or nothing to do with coolant bypass. It probably will read higher than the ECM temp sensor in the intake--that's not unusual.

 

[GmTard89]

so I did both bypass the heater core and wrapped the sensor with silicone and no change. temps still normal at intake. its only on warm up it spikes . idk i'm starting to want the oem hooked up and and drill and tap intake for this mechanical . but my only concern is would a oem sensor show the same issue if there is one ?

 

[95 Tahoe]

I have a temperature probe in the passenger side head since my dash gauge always reads low. It did the same thing on me. It would read up to 250F before the thermostat opened at 195. I went to a 185 thermostat and drilled (2) 1/8 holes in it it to allow some circulation. Now it hits about 210 before the thermostat opens. I really don't think it was ever a problem but it was scaring me with a $2000 rebuild I just dropped in.