Coolant gauge fluctuates and heater gets cold

[flashgordon]

Hay Guys, I have ran a crossed this problem several time and have NEVER been able to find the solution.
Yes stant was replace, and both gasket in housing were replace the 2nt time.

Gauge comes up to temp, heater gets warm, gauge falls to almost cold, heat get almost cold also.
it continuously cycle like that.
at 20*F it's not much of a problem but below 0 it becomes dangerous!

Cardboard in front of the radiator helps,...........But theres got to be a fix out there some wheres??????

Even when to Geno's Garage, but couldn't find a answer

Help, ideas sugestion,.....thoughts, theory's, would be greatly appreciated

Flash.

[flashgordon]

Hay Guys, I have ran a crossed this problem several time and have NEVER been able to find the solution.
Yes stant was replace, and both gasket in housing were replace the 2nt time.

Gauge comes up to temp, heater gets warm, gauge falls to almost cold, heat get almost cold also.
it continuously cycle like that.
at 20*F it's not much of a problem but below 0 it becomes dangerous!

Cardboard in front of the radiator helps,...........But there's got to be a fix out there some wheres??????

Even when to Geno's Garage, but couldn't find a answer

Help, ideas suggestion,.....thoughts, theory's, would be greatly appreciated

Flash.

By the way this is a 12V not 24V, 97:hs:(sorry wrong section) I gave up on it......again
And my buddy's dad has it back, but i could get it back...............my only Idea is a slight head gasket leak.............but that would cause air to build up behind the t-stat, getting too hot before the t-stat opened...
I took it up this step hill full throttle, drove it nice and gent holding about 40 mph................ temp fell the same way in both situations................
At idle for 20 minutes temp gauge held steady..............2500 rpm in N gauge would would fall but not quite down to the beginning of the temp range of the gauge like before.
Opens at the proper temp, just don't close until the block is cool.
Defroster heat and temp gauge work in Parallel.
I even remove the fan from the motor, and at 20*F out Friday, the eng had no idea it was missing. It didn't change how it worked at all.
Pinched off the little bypass tube that gos from in front of the T-stat to the other side of it..........No change.................................................


Flash

[PToombs]

To check the headgasket, put a radiator testor on it. Start the engine, and watch the gauge. If the gasket or head is bad, the gauge should go up. A bad gasket almost makes sense, air builds up near the 'stat, and goes down the heater tube, no flow, no heat. The only other thing I can think of is a bad 'stat. It should close promtly when it starts to cool off. Pull it out, put it in a pan of water with a thermometer, and hot it up. See when it opens, add cold water, see when it closes.
Hope this helps.

[burnt_servo]

something else to look for , with a bad headgasket , or cracked head on a diesel , look for either a oily film in the coolant , black / oily ring in the rad overflow and or black / oily residue in and around the rad cap .

does the coolant look like carbonated water ?

[flashgordon]

To check the headgasket, put a radiator testor on it. Start the engine, and watch the gauge. If the gasket or head is bad, the gauge should go up. A bad gasket almost makes sense, air builds up near the 'stat, and goes down the heater tube, no flow, no heat. The only other thing I can think of is a bad 'stat. It should close promtly when it starts to cool off. Pull it out, put it in a pan of water with a thermometer, and hot it up. See when it opens, add cold water, see when it closes.
Hope this helps.

Thanks for you input, I do appreciate!!!!!!

A bad t- stat would make total sence...... but replaced with mopar t-stat two time last year, before i gave up on it. This year started with fresh Napa T-stat, then with a Mopar one again.......and replace the tube type gasket as well and the small on (that i didn't now was in there ) that the t-stat face sets or seats at........... No change

I will try the pressure tester, and the t-stat in a pan if we decide to replace it again This is a totally stock p pump 12 (It could most definitely have some timing added to it.) Not a vary happy eng when cold. and will let yeah know if you try and move it with out some warming of it.

burnt_servo.

coolant was clean(no sign of oil) and good to -45* f every time i drained it to replace the t-stat

Makes me thing the radiator is to big and causing the two quick, of cool down going back in to the block when it's )0*F out side..............but if that was the case there would be all kinds of buss on the net about it.
this is kind of a rare problem......................??????But it can't be that Rare, have seen the problem with "2" different truck of the same era.nether one was fixed with a t-state and gasket

[PToombs]

Flash, there is only 1 gasket in there! It should be a tube looking thing, like a piece of radiator hose. It seals against the lip in the head and one in the housing, the lifting eye floats in the middle. If you are buying the "kit" from a cummins dealer, (cummins brand kit) it has a blue template to check size of the hole. Early heads had a small diameter hole, which had to be ground out to the template size to make the new 'stat fit. Not sure if this is what you are calling a "gasket".

[flashgordon]

Flash, there is only 1 gasket in there! It should be a tube looking thing, like a piece of radiator hose. It seals against the lip in the head and one in the housing, the lifting eye floats in the middle. If you are buying the "kit" from a cummins dealer, (cummins brand kit) it has a blue template to check size of the hole. Early heads had a small diameter hole, which had to be ground out to the template size to make the new 'stat fit. Not sure if this is what you are calling a "gasket".

Pete, thanks for bouncing ideas around with me!!!!!

The housing in question, with the temple is 89-90 ve pump eng

this one is a 97 p7100 head. Yes there is 2 gasket, and i didn't know this unill i was looking at a blow-up of the housing.........there real are 2, and the original on was still there and seaminly in good shape..........But i did replace the tube and the nylon gasket the last time...................I'm going to recheck the t-housing spec and what years that was affected, How ever, tomarrow..........Just to make sure i'm not blowing smoke

Flash

[flashgordon]

the t-stat housing was inlarge from the factory, april of 90

Flash

[PToombs]

I was going to say, I have never seen a small hole head. The guys at work remember doing several. Of course, the industrial version was out years before the truck version.

[flashgordon]

I was going to say, I have never seen a small hole head. The guys at work remember doing several. Of course, the industrial version was out years before the truck version.

Yeah i was reading in the survice manual..........actualy it was a TSB manual for 91. any ways, the prosedure was simply, get a die grinder. with a bur on it, and hog it out


Flash