92 GMC C1500 Coolant Temperature

[eshawl]

Is it normal for my coolant temperature to read around 150? I have replaced the coolant, coolant sensor, coolant switch and thermostat (195 stant) and it still reads the same as it did prior to making any changes. If anything it reads slightly cooler now.

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[Erik the Awful]

I don't trust the factory gauges to be accurate. Do you have an infrared thermometer or any alternative way of verifying the temperature? Also, is your coolant topped off? An air pocket can give you a false reading.

 

[eshawl]

I don't trust the factory gauges to be accurate. Do you have an infrared thermometer or any alternative way of verifying the temperature? Also, is your coolant topped off? An air pocket can give you a false reading.

radiator and overflow are at the max fill line and haven't moved now for months.

 

[Frank Enstein]

The numbers on the gauge are meaningless. They mean as much as Ferd's NORMAL temperature gauges.

Find out what temperature is "Normal" and remember where the needle is pointing.

If you're REALLY OCD (like me) about it you can pull the needle off the gauge (a fork woks really well) and push it back on pointing at the actual temperature.

 

[DerekTheGreat]

A fork! Thank you, Frank. Been trying to think of what to use on my speedometer to reset that thing, wasn't sure.

Another thing the OP can try is a different sending unit- this fixed my wife's truck, which also read low temp wise.

 

[Frank Enstein]

You're Welcome!

 

[tayto]

worked on a 92 gmc recently. cooling system was in bad shape. did an extensive flush replaced thermostat,etc. before would sit just under half way, now reads like OPs does between 2nd and 3rd mark. Hooked up scan tool and ECU says 190, gauge reads 40* LOWER. Read an obscure post on fullsizechevy a while back and someone said they put in a sending unit from a 96-00 c/k truck (ac delco 213-820) and their gauge is more accurate. i have not tried yet....

 

[DerekTheGreat]

Wow, I'm amazed at how many people neglect the cooling system. The "new" used engine which went in my truck suffered the same fate. When I replaced the water pump, I used the increased access to flush out the system until the water came back clear. Took a long time going from the heater hose, thermostat housing and water jacket holes.

I think what causes that is tap water mixed in with coolant. I picked up a 1979 G10 last year, seemingly all original. Coolant was clear green still despite sitting for 20 years. Someone explain that to me...

 

[tayto]

i used a quart of motorcraft VC9 flush. removed thermostat, lower rad hose and block drains. flushed with garden hose until clear, added flush and drove around for a day. then dumped and flushed block and rad with garden hose with engine running. refilled with dexcool, after a week have a small amount of sediment in the reservoir but nothing "bad". it gets like this from using cheap coolant and never changing it. our tap water is very good where I live, but I still buy jugs of water to mix with coolant. im also a big fan of removing the block drains when i do a regular maintenance flush. i replace all the steel drain plugs with brass ones.

 

[Schurkey]

Is it normal for my coolant temperature to read around 150?

NO.

I have replaced the coolant, coolant sensor, coolant switch and thermostat (195 stant) and it still reads the same as it did prior to making any changes. If anything it reads slightly cooler now.

There's a dozen things this could be, but all diagnosing starts by connecting a scan tool so you can compare the engine coolant temperature the computer thinks is correct, to the engine coolant temperature the gauge thinks is correct.

Wild Guess: The ECM has the correct coolant temperature. The gauge is wrong. The gauge may be wrong due to any one--or a combination--of several potential problems.
The gauge sending unit may be incorrect, or faulty, or installed with thread tape instead of a minimal amount of chemical sealer.
The wiring between gauge and sending unit could be faulty
The gauge could be faulty
The instrument cluster circuitry could be faulty
The instrument cluster power or ground could be faulty.

i used a quart of motorcraft VC9 flush. removed thermostat, lower rad hose and block drains. flushed with garden hose until clear, added flush and drove around for a day. then dumped and flushed block and rad with garden hose with engine running. refilled with dexcool, after a week have a small amount of sediment in the reservoir but nothing "bad"... ...im also a big fan of removing the block drains when i do a regular maintenance flush. i replace all the steel drain plugs with brass ones.

Wise man.

I don't know about the Motorcraft VC9--that's a product I've never tried and have no opinion of.

"Flushing" a cooling system but NOT removing the block drains on each bank of a V-6 or V-8 is crazy. Block drains are a pain in the asp, but it's essential to remove them now and again to remove the debris that falls to the bottom of the water jacket--and also to remove the flush water that would otherwise dilute the antifreeze.

My vehicles get brass draincocks in the block drain holes; vehicles I do for other people get brass plugs. I never re-use steel or iron block drain plugs except when that "steel plug" is a knock sensor body that's intended to be crammed into a block drain hole, as is common on small-block Chevies and the similar 90 degree V-6.