Pulling into my garage a couple of nights ago just in time for the red light on my temperature gage to light up, and then I had a boil over. The next morning I filled the system back up with a 50/50 mix per the sticky on this site, taking care to vent properly etc. BTW, I have checked for leaks and found none, and there are no symptoms of any coolant getting into the oil system as well. After driving it yesterday for about 15 miles, I noticed the temperature gage moving toward high, then back to normal, then toward high again and back to normal by the time I got home. Fluid level was normal at operating temperature. Today I checked when cold and it was down about 1 1/2" in the reservoir, which I have topped it off to the cold level arrow.
My questions: Do you think the thermostat is going bad? Or the reservoir pressure cap? Any other thoughts?
Thanks in advance for any insight to this.

 

I would start by checking your belt tension, if it is to loose the belt will not spin the water pump fast enough to cool the engine.

 

I did check it, and though it seems to be the original (meaning maybe it has stretched a bit) it doesn't seem to have any excessive play at +/- 1/2". I do have a new one to put on, and will do just that next chance I get.

Is it possible I still have some air trapped in the system, even though I followed the directions in your sticky to the letter? If so, I guess draining the system down and starting over again wouldn't hurt. Dropping the t-stat for the drain would let me look at it, if only I knew how to judge if the stat is good or bad. This would be my first look at a Landy t-stat.

 

Usually when a t-stat fails they fail open and the the engine runs cold, heater wont work, MPG drops.
But they can fail in the closed position, they are cheap, it would not hurt to replace it along with the radiator cap.
Replace the t-stat, belt and radiator cap and see what happens.
You wont need to drain the system and start over, just remove the t-stat and then refill and re-bleed the system.
It is possible that you still have air in the system, if you want to try and re-bleed it then after it is warm rev the engine to 2,000 rpm and hold it for a min or so, that will help to force any stubborn air pockets out.

 

As usual, you have been most helpful. I'll go through it all and let you know how it went. Thank you very much!

 

Okay - new belt, thermostat, and existing cap holds pressure very well and I still have the problem. It runs hot at speeds over 40-45 but if I slow down to 30-ish it returns back to normal temperature. No leaks apparent anywhere on the garage floor or in the engine oil. The heater works well BTW.
Possible head gasket leaking into the exhaust side? Faulty temperature sensor? Partially clogged radiator? Failing water pump? Even though I have followed bleeding procedure is it possible I still have air trapped in the system? I do have to add a half-pint of coolant(+/-) after the engine has totally cooled.
I'm starting to have fun now .... help!

 

I doubt that you have an air pocket if you bled it as per the sticky. It is normal to have to add coolant for a couple days after bleeding as the final pockets of air get worked out. Probably a bad radiator then. Is the radiator pretty clean on the outside? Also I assume the outside of your engine is not all caked with grease?

 

Radiator is pretty clean, showing no leak stains. The engine is semi-dirty but not grease-caked. I have bled it per the sticky twice now, once when I replaced the top hose a month ago and again yesterday when I replaced the thermostat. Thanks for the suggestions.
Would I have intermittent overheating with a bad radiator (as opposed to constant overheating)?

 

With a bad radiator you would be OK when you start your truck and idle for a while but once you start to put any sort of load on the engine it will overheat going back to idle will allow things to cool down. With a good radiator your the faster you go the better for cooling and idling is what would cause the highest temps. A bad water pump means no coolant circulation so you would not even necessarily see the overheating until it is way way too late.

 

Okay, going with the bad radiator concept, is it possible it has become clogged due to the use of Dexcool? Much has been written about how this particular coolant has caused clogging and eventual head gasket failure.
If I flush the system and replace with another brand, say Peak Global, would this solve the problem? Further, how do I get a complete flush to rid the system of all Dexcool?