Another thread about engine not reaching operating temp

[jacobarber]

This is a '93 Blazer Cheyenne. I got this truck from my dad after he passed, put some work to make sure it would run and drive safely, etc.

The temp gauge hasn't worked since I had it, so I decided to get that fixed. I replaced the temp sensor on the driver's side cylinder head between the spark plugs. The gauge finally came to life, but just a little. The needle never went above the halfway mark between 100 & 210.

I suspected someone put a 160 degree thermostat in, so I took the neck off and saw a 195 degree t-stat. The gasket had pretty much disappeared, so I figured coolant was getting by regardless. Replaced the thermostat, thermostat o-ring, and water neck gasket. Tightened everything down, and even replaced the upper radiator hose which seemed to be rubbing on the alternator bracket.

Ok, got it all back together and took it for a drive. It is just under 60 degrees outside and I drove for ~20 minutes. Still wouldn't move above that same halfway mark between 100 and 210.

So I've replaced the coolant temp sensor, thermostat, t-stat o-ring, water neck gasket, and upper radiator hose. The gauge works but temp doesn't go past ~150-160?

Thoughts on what to try next?

 

[someotherguy]

Start by not trusting the gauge. It works on a range of resistance, so the higher the resistance the colder it reads. Old electrical circuits develop resistance in a number of places so any added trouble in the circuit and you get a lower-than-actual reading at the gauge, if that makes sense.

Best bet is to start with an IR thermometer and get the engine fully warmed up, then scan around the intake in the area of the thermostat housing until you see the highest temperature reading. You should be able to get a read very close to the thermostat rating. If you don't, then it's time to investigate further into why the engine isn't coming up to temp.

My money is on the gauge being inaccurate. You can address issues in the circuit like cleaning up grounds on the engine harness (at and next to the thermostat housing), dash cluster (single black wire on a metal tab under the dash next to the diag connector), and other misc. grounds under the hood like the braided straps that go between the rear of the passenger side head to the firewall and from firewall to frame, small ground from battery to fender, etc.

Once you've addressed all those and the gauge still doesn't match actual temp, you might consider the "hack" .. er.. "calibrate" approach and remove the lens from the gauge cluster and gently reposition the needle to match the actual temperature reading you observe with the thermometer.

Richard

 

[GoToGuy]

When you say " replaced the thermostat" . What context are you using? Replaced as in installed new thermostat? Or as replaced as reinstalled the current thermostat?
How hot is the heater air at full hot full blast. After that drive could you grab the radiator hose and hold onto it?

 

[jacobarber]

The context is that I installed a new thermostat. I did use an IR thermometer and the block right next to the coolant temp sensor was reading ~200, which does lead me to think the gauge is just wildly off. I did not check next to the thermostat housing, nor did I touch the hose. Can definitely give that a try tomorrow.

 

[someotherguy]

The context is that I installed a new thermostat. I did use an IR thermometer and the block right next to the coolant temp sensor was reading ~200, which does lead me to think the gauge is just wildly off. I did not check next to the thermostat housing, nor did I touch the hose. Can definitely give that a try tomorrow.

Sounds like engine is getting up to temp just fine, and the gauge is suspect. These trucks are notorious for reading "cold" more often than not. To me, it seems like a combination of inaccurate gauge, and excess resistance in the circuit. I'd start with cleaning up and ensuring all the grounds are good, before going in to tweak the needle.

Richard

 

[east302]

That’s about where my 98s have always read…1/2 to 3/4 of the way to 210 with the coolant temperature sensor reporting around the thermostat setpoint.

I guess the TBI’s temperature sensor can be read with a scanner? That would be good confirmation, but I’d bet that you’re in “as good as it gets” territory if everything else checks out.

I wonder how many dealers back in the day fielded complaints about those temperature “gauges”. The little tick marks imply that it’s displaying a fairly specific value when it really isn’t…not that anyone could figure out what each mark was supposed to represent without doing math in their head. I guess they added the tick marks to make it match the other gauges.

 

[someotherguy]

That’s about where my 98s have always read…1/2 to 3/4 of the way to 210 with the coolant temperature sensor reporting around the thermostat setpoint.

I guess the TBI’s temperature sensor can be read with a scanner? That would be good confirmation, but I’d bet that you’re in “as good as it gets” territory if everything else checks out.

I wonder how many dealers back in the day fielded complaints about those temperature “gauges”. The little tick marks imply that it’s displaying a fairly specific value when it really isn’t…not that anyone could figure out what each mark was supposed to represent without doing math in their head. I guess they added the tick marks to make it match the other gauges.

You can check the temperature sender with an ohmmeter, like the CTS. Can't read the dash temp sender with a scanner as it has no input to the ECM/PCM; only the CTS does. Vortec, TBI, doesn't matter - same setup. One talks to the dash and the other talks to the PCM.

Richard

 

[Hipster]

Some senders are for a guage some are for a light, verify you have the correct one, new doesn't mean good or correct packaging/identification these days