Overheating- all of a sudden

[68C15]

Originally Posted by Shyguy

How full are you filling the radiator? I usually fill mine until it is about 2" down allowing room for expansion and so far have not had an overflow problem.

Danny - Southeast Missouri

BINGO!!!!!!!!!!!

but when you switch to a reserve bottle system then you need to FILL the radiator.

as Andy said I would wire the system to run only with the key on.

[WinDancer]

The bottom line here, for me, is the fact that the cooling system has worked well for the past year.

I didn't change anything and now it isn't even barely working.

I will check with my heat gun and see if that will trigger the electric fans to come on. I am off now to put in the new water thermostat and the radiator cap.

Will check back after a bit with an update.

Thanks to all...

[ChevLoRay]

That's the thing about the mechanical thermostat....they stick without warning. When they stick, things get funky, fast. My money is still on the mechanical thermostat.....get one, pull the thermostat housing, the thermostat, and clean all of the gasket goo off of it and the intake. Install the new thermostat, being careful not to install it upside down....it has happened. Be sure to use a new gasket on the thermostat housing. Some are self-adhesive, some require adhesive. When you have everything ready to bolt down, don't use too much torque on the bolts if your housing is aluminum. Some are, some are cast iron. Make sure all of the hose clamps are tight.

[WinDancer]

Didn't have the most enjoyable day with the truck.
The fan temp sensor is between the radiator and the fan assemblies, so I wasn't able to test it.
I removed the first bolt from the thermostat. The second bolt was very tough to turn. I ended up with a cheater bar over the the ratchet handle, and the bolt finally broke off.
After several hours with different plans I gave up and just broke the thermostat housing and removed the problem bolt.
I will go to town tomorrow and see if I can scare up another housing and a bolt, then put everything back together and see what happens with the cooling fan not running.

[ChevLoRay]

Sorry you had trouble with the bolt. It sucks to break one off. The thermostat housings are stock items at my NAPA store....should be in your area, too. They'll be cast iron. There's always the aftermarket for resources, too. Should be able to find one with a chrome finish....O'Reilly's???

[berencam]

id bet a hundred bucks its the thermostat, even with the fans not running correctly( if they aren't) a four core rad will keep that engine at least on the hot side, and not boiling the coolant at just a idle. the reason you are still boiling water even with the fans overrided on is because your thermo got stuck in the closed position thus your pump isn't pumping water through the block. just my .02

[ChevLoRay]

I think he's on the same page with us, now. The fact of the matter is that the pump will run, but the stuck mechanical thermostat (like you said) won't let water/coolant circulate. To some folks the whole thing is hard to understand, from a mechanical concept. The way I used to know for sure that a thermostat was stuck, was when one came into the station, steam rolling out from under the hood and usually making a honking sound as the steam passed between the gasket of the radiator cap and the bottom of the radiator filler neck.

If anyone encounters such an event, do NOT take the cap off of the radiator!! Repeat, DO NOT take the cap off of the radiator!! The hot coolant will blow out of the filler neck and you will get burned by it. Get away from the radiator and just be patient. When it has stopped with the honking sound and the steam has dissipated and is no longer blowing, THEN and ONLY THEN can you begin to SAFELY deal with the hot radiator. Start by pouring cool water on top of the radiator cap, doing so for several minutes. When there is no more steam or coolant blowing out, loosen the cap to the first stop. At that time, there may be more coolant that leaks out, but the cap should stay on the radiator. When all of the pressure has stopped venting from the radiator, go ahead and take the cap off. After the engine has cooled down, you can begin the process of replacing the thermostat.

[WinDancer]

Schucks Auto Parts had a new housing [polished billet, all they had] for the truck.

Auto Zone had a pressure tester that they loan out for free! I didn't even buy any parts there. They just moved up on my list of where to go. They charge you the cost of a new tester [$75], then refund in full when you return it.

SOOOOO

I installed all the parts [the new housing has an o-ring, so no gasket. The o-ring seemed to droop when you turned it to the install position so I added a little tiny bit of grease in the o-ring slot and that held it while installing it], brought the motor to operating temp with the cap off, then installed the new cap.

I let the truck run at idle for about 30 minutes and it got warm but not hot- still burped a little water when the coolant got hot- then settled down. The water in the radiator at this point was not hot- I dipped my fingers in the radiator and the water was still cool. The heater hoses were all very hot- lots of heat from the heater.

I drove into town for gas after all the idling and the temp never got past normal.

Not sure if it is 'fixed' yet or not. Will drive it to work for a couple of weeks and keep a close watch on it.

Thanks to all for your thoughts and suggestions!

[69TowRig]

Well you beat me to my suggestion, I think your cap was failing. The cap is vital to the operation of the cooling system because it allows the water to build up pressure. High pressure water can take more heat before boiling off. If the cap goes bad then the pressure does not build and instead the temperature rises instead. Since the water expands the only place it can go it out the now inoperable cap, once it hits ambient air it turns to steam.

[ChevLoRay]

Originally Posted by WinDancer

I drove into town for gas after all the idling and the temp never got past normal.

Not sure if it is 'fixed' yet or not. Will drive it to work for a couple of weeks and keep a close watch on it.

Thanks to all for your thoughts and suggestions!

You would have never left your house, if it wasn't fixed. It would have continued to heat up and then you'd have seen a replay of your first post. If you put a new thermostat in it and a new t-stat housing to replace the one that broke, you fixed it. Congrats. Now, go forth in peace and feel confident in what you got done.

[Longhorn Man]

Did the fan ever come on this time?

[ChevLoRay]

I'm gonna hazard a guess that there was no problem with the electric fans. If the sensor for those fans was on a part of the radiator that didn't get hot enough to trigger it, they wouldn't come on until you hit the override switch. I'm gonna guess they are working correctly.

[WinDancer]

It was the fan thermostat. I replaced that today and the fans now come on when it gets above normal and cools back down correctly.

Thanks for all the responses and suggestions- I love this board!