Cooling system issue/questions

[bobweiser]

Thanks for all the help I've gotten so far. I am putting this into one post to try to resolve this issue.

 

'89 Comanche 4.0l - sat for a few years, back running.

Installed full gauges and new sensors

After truck runs for 5-10 minutes, gauge moves up and sits right about red line (240)

Doesn't boil over and I get get heat in the truck.

However, coolant tank does not change levels.

Bled system, no change.

Installed new pressure cap, no change.

Temps from a laser themometer show me anywhere from 180-220

Planning on change thermostat this week.

Find it strange that it goes only to 240, so far no higher, I have heat, no boil over, but no coolant level change either.

 

Looking for advice.

[BLHTAZ]

You might try changing the gauge itself. If you are verifying that the temp is within normal operating range, then the gauge is the next likely culprit. My oil pressure gauge stayed just under the 20 PSI mark even after changing the oil pump, rods & mains, but all was good when I replaced the gauge.

 

Do the t-stat first...see what happens.

[chicofuentes0224]

Bob, where are you getting the readings from your laser thermometer?

[bobweiser]

I've shot temps of the thermostat housing, all the hoses, the plastic tanks, and the back of the block where the temp sensor is (this is the highest reading). I may have two issues going on. Idling in the driveway for 10 min, the gauge goes to the read line and stops. The heater hoses are warm/hot, heat in the truck, but the radiator hoses are cold. I also never seem to get the coolant tank to get full, it's at the proper level cold.

 

Odds are the gauge is wrong. This doesn't explain the pressure tank. Unless, the cap I replaced fixed this and I didn't let the truck run long enough for the thermostat to open and pressure to build. Regardless, I'm changing the thermostat and flushing the system to start from square one. Knowing my luck, I'll get air in the system that I won't be able to bleed off. :wall:

[Oizarod115]

start with a thermostat, flush (like you said) and a temp-sender. the one for the back of the head with the wire that just pokes on. this fixed my problems. my gauge would read 210 (normal running temp) at 160.

 

replaced temp sender and problems are all gone, laser thermometer gets within 10 degrees of the gauge most spots.

[Eagle]

You may indeed have multiple things going on. By all means, start with the thermostat, since the evidence of the hoses is what they call a "clue."

 

The other thing to look for is if it heats up quickly when you're stopped, and then cools back down toward normal as soon as you get rolling again. That indicates that the viscous fan coupling on the mechanical fan isn't doing the job, and at rest the fan isn't pulling enough air through the radiator to cool the system. Once you're rolling, vehicle motion forces air through the radiator, so the temp drops back down.