Overheating was caused by a stuck open thermostat that was less than three days old from O'Reilly's Auto Parts. However there is damage I believe to the engine. The engine now has blowby out the fill tube it never had before. But the thing that has me worried and am seeking advice on is a metallic sound that can now be heard with oil fill cap off seemingly from within the front cover. I'm discounting the dowell pin theory since the pictures I've seen show the pin is not behind any moving parts that it might rub up against if only partially out. Have/Had a cross county trip planned and my confidence in my rig is now zero.

 

Stuck-open thermostat shouldn't cause overheating. Should be the opposite.

Did you mean stuck partially closed?

If you ran the engine on an extended period while overheating damage may have occured to the pistons and cyl walls or the head gaskets causing the blowback. As to the metallic sounds up front, i don't know, but I hear a lot of them on mine and sound like normal.

 

Might not be the dowel, but the case bolts can indeed back out and rub against the gears. Rebal has posted that picture many times.
Another possibility is the pin is laying on the gears and rolling, mine did that for some period of time before being ejected thru the case.

Get her apart and find out before something bad does happen.

As for damage, blowby is out of all diesels, the key is how much. Is it still overheating, or do you see oil or water mixed?

 

Truck is running at steady temperature and holding coolant. Stuck open is correct as stated. I think it allowed the internal bypass to be uncovered preventing coolant from being circuated into radiator. Service manual says overheating will occur if no thermostat is in place due to this bypass. Thanks for the ideas on case bolts but its hard for me to imagine since there was none before, just like there was zero visible blowby before. Owner says they shut down as soon as they noticed gauge was at "H", but I'll never know the complete truth here, though I have no reason to doubt owners statements. I believe I have attached a photo of the stuck thermostat (on left) and the replacement one on the right for reference. Also no obvious evidence of mixing in radiator or crankcase at this time.

 

Interesting. I thought the bypass hose being open (when thermostat is closed) is to allow closed loop flow of coolant through the water pump, in the meantime flow through the radiator is blocked by the closed thermostat. This is called "bypassing" the radiator. When the thermostat opens, it blocks the bypass passage while the opened thermostat allows flow through the radiator. At this time the water pump does its job pumping through the radiator and block,etc. Instead of "spinning its wheels" in bypass mode.

Now I can understand an overheat condition when the thermostat is stuck PARTIALLY open (unable to block the bypass hole completely) in this case the water pump won't be able to efficiently circulate the coolant because of the partial leak through the bypass hole.

I'm interested to know where in the manual (I have the FSM) you found the explanation of the overheat. It's always good to learn new things.

 

Experiencing the exact same problem! Metallic noise is very discomforting. My truck did not even have a thermostat in it for some time! Does anyone know if this could have damaged it?

 

Can you hear it with the cap on? Have you ever listened for this noise before you had the over heat problem? Don't forget there are quite a few gears spinning in there.

 

Partially open, open, My choice of words describing the thermostats state may not be the best. Please see the pic I posted. '93 flatbed-yes I have listened before and no noise. I've been looking for a replacement engine for the crewcab after losing a cylinder (see another post) and some others have had this same lite ticking? as I'll call it while some clearly did not. One engine seller, with diminished hearing thought I was making it up as a way to grind him on price. He recently apologized after having his own mechanic listen. I appreciate there is a lot of metal to metal contact inside the cover, but this noise was not there before. period. Now whether its coincidental or related to the overheating is my dilema. Nobody has suggested anything heat related so I'm leaning toward the coincidental. Tried to wiggle/move cover but unsuccessful, but I'm not rejecting this as a possible cause. And no I can't hear it with oil fill cap on.

 

To JJdiesel 1990, I doubt you damaged it without a thermostat unless you were operating it at excessive temperature, running with needle on or above the "H" on the factory gauge or above 220-230F on a manual gauge.

 

To ClassA4x4, I read it in the 1990 diesel engine supplement to the 1990 FSM for dodge trucks, cooling system section, page 7-8.

 

I had a metal clinking noise at one point too. I disconnected the belt, removed things, and eventually figured out it was my 89/90 Non-IC style vacuum pump that was making the noise. The front bearing was going bad. I switched to an IC style vacuum pump set-up all has been good.

Did you install the thermostat yourself?

 

To thrashingcows, sadly yes it was me who installed the thermostat and radiator hoses for the owner who loans me the truck just about anytime I need it since the crewcab has been down. Thank you for the suggestion on the vacuum pump. The front seal on the power steering pump has been dribbling a little so pulling it and the vacuum pump need to be done at some point to fix leak. If I weren't such a newbie to the world of diesels I probably would not be so freaked out over little noises and such.

 

I had a random clicking on the truck I just bought, it ended up being the waterpump, the pulley would move in and out and the impeller itself would impact along with the collar on the shaft as it moved in and out. It would only do it when it was first started then it seemed to go away, but the sound carried through the entire front case. I took the belt off and it was very obvious the bearings were gone. It didnt leak out the weep hole either, anyways just a thought.

 

To taterfarm I had considered that and pulled the pump thinking a loose/broken impeller was partially to blame for poor cooling. It all checked out fine so I put it back. Thanks for the idea.

 

I thought it was common knowledge on here that the thermostat, when it opens, closes off a by-pass that redirects coolant to circulate back through the block.