What happens if a thermostat sticks closed?

[whatnot]

My '95 truck just got a new problem.
I am hoping it is just the thermostat.

[StephenA]

What are the symptoms? Thermostat stuck closed means no circulation of cooling fluid through the radiator, guaranteed to pop your cork in a bad way...
BTW - John Kennedy has most robertshaw T-stats in stock, & I finally found a vendor for the ones out of stock. In any case it's a very easy replacement (don't forget the gasket!). These engines don't survive much overheating.
Stephen

[whatnot]

The symptoms are that the temp gauge is going way up then droping down real fast all at once. Then I start getting the low coolant light. (yes, the gauge is reading the correct temp, because it gets hot enough to boil)

My brother just came over and asked what could be causing a problem on his truck.('94 6.5td) It just started the exact same thing. It must be contagious.

[charliepeterson]

In my experiance most thermostats fail partially open. The engine will warm up slower. Take a look at debris inbetween the radiator and A/C condensor. The water pump could be failing, or the radiator itself might have lost a few passes at the bottom. Try putting your hand along the sides looking for cold spots.

[whatnot]

I think that it is much worse than the thermostat.
We tried changing it on my brother's truck with one we had here.
It didn't help any but then the truck started smoking pretty good.
I rotated the overflow tube up on mine and reved the enging to around 2000 rpm for a few seconds and it started spraying coolant out. The gauge was only about 1/3 of the way up because it had been sitting for a few hours.

So, is it most likely head gaskets? Is it just coincidence that two truck go at the same time?

[skip460]

I fear you have the cracked head problem that the 6.2 and 6.5 get. My 95 did the same thing.The space between the exhaust and intake valves crack and if its deep enough then you have pressurized cooling system problems and smoke from the exhaust and wildley fluctuating temp guage.There is articles explaining this on the diesel page and how to fix it. All 8 of mine were cracked, but only one was all the way through. I bought the kit and sleeved all the passages.Good luck

Kevin
1995 C2500 222,000 6.5L TD with heath PMD isolator and soon torquemaster chip

[ucdavis]

Whatnot-
Driving under these conditions is hazardous to your wallet. Ask Journeydog. His was doing just about what yours is & he'll be back on the road soon but about 5 figures lighter.
For coolant leaks @ head gasket, check oil for water, coolant smell or foamy consistency, & watch smoke condition (increased white smoke look &/or coolant smell indicate leak to cylinder).
For cooling check:
1) bugs. yearly water jetting might produce clean look to AC condenser & motor side of rad, but the space between condenser & rad can accumulate debris over the years that can't be seen till you loosen & tilt the condenser. Probably #1 cause of overheating.
2) bad coolant or coolant proportions; do hydrometer check & use distilled water
3) stats need changing; simple & cheap (except for the stoopid rad. drain location, oh well).
4) radiator corrosion over time = loss of capacity.
5) pinhole coolant leak in hose, collapse of hose, etc.
6) low pump output due to accumulated corrosion or pump vane deterioration
7) overheating due to mods not respecting cooling needs or overstressing stock config w/repeated high GVW.
8) fan clutch failing (can't hear the roar no more)
With #3-6 the fan clutch may not engage much or at all.
The basic message from the Cracked Casting Club is "get dirty if you have to, but find that heat problem & solve it, & don't drive it till you do." If you worked thru above list every few years (#1 every year) & change all hoses/stats B4 trouble, it'd be cheap. Good luck.

[Petrella]

whatnot, i had the exact same problem as you did, it turned out unfortunately i had to replace the drivers side head gasket on my 94 6.5. The head though was ok.

[whatnot]

Could a leaking head gasket cause black smoke out the exhaust? Mine has been smoking for about 6 months under load unless I give it over 11 Lbs of boost.
My brother's truck just started to smoke some a couple weeks ago.

What should I expect to have to pay to have the head gaskets replaced? The local diesel shop gets $55 per hour. Is that about average?

Thanks