I've got a 1990 W250 that I have been working on a lot as of late. From the moment I bought the truck, the factory gauge indicated that it was running warmer than ideal (right of center). So, I pulled both radiator hoses and replaced them, flushed the system with distilled water and a chemical flush, flushed with distilled water again, and filled with brand new coolant. This did nothing other than make it worse. As soon as the truck is driving, the temp gauge steadily increases until I have to shut it off for fear of it getting hotter. The other question I have is, my manual states that the cooling system should hold about 16.5 qts. I put about 6 qts. in and it would not take any more. Obviously more coolant should (in theory) solve my heat problem, but how do I get more in? I had the heat cranked up (though it was still only blowing cold air) in order to open the thermostat, and that did nothing. I changed oil the other day and it was not diluted by coolant, and a block leak tester indicated that my head gasket is fine. I'm not sure where to look next... Any input would be greatly appreciated.

Thanks in advance,
Jake

 

Do you know if the thermostat is even opening?

My first thought would be to run it for a bit without a thermostat to see if that helps.

 

I agree with Pat.
You mentioning that the gauge reads hot , but no heat is getting to the heater core makes me wonder.
Is the radiator hot to the touch when it reads hot by the less than awesome stock dash temp gauge?
Are both the radiator hoses hot after a good ride?
I am thinking something, somewhere is not flowing enough, or maybe even at all.
A closed thermostat would do it.

 

This is what I'm leaning towards as well. The lower radiator hose seems to have no fluid in it whatsoever... When I squeeze it, it just feels mushy instead of full. So run it with the heater off and see what it does?

 

I would pull the thermostat out completely and run it with no Stat to check.
When you flushed the system out did the water flow freely through the engine and the radiator?

 

It seemed to flow just fine... I filled it with distilled water, ran it for a few minutes, opened the petcock on the bottom of the radiator, and it drained for about 10 minutes. After running the cleaner in the system, I opened the petcock on the bottom of the rad again, and while the truck was running, I kept pouring in fresh water to flush out the cleaner. I then shut the truck off and poured a bit more water in and watched it drip right out of the bottom into my bucket - so I'm assuming it was flowing as freely as it could

 

Are you sure it was also running through the engine??
Did the water get hot?
I ask as you might have just been running water through your Radiator IF the Stat is broken, installed backwards or otherwise not opening...

 

Now that you say that, it's got to be the thermostat. The temp gauge was reading hot and the water was nowhere near hot. I feel stupid for missing that one... So you would remove the thermostat and run the truck for a bit just to make sure that it is the thermostat?

 

Yes.
Then try dropping the old 'Stat in a pot of water and heat it up.
It will open up before it boils, or at least it SHOULD. Haha
If you have a candy thermometer you could check to see what temp it does open up at as well.

Yeah I think you are on the right track now.

 

I will try that within the next day or two and let you know what I find. Thanks a ton!

 

I don't know about the older models, but usually the heater core gets water even if the T-stat is closed.

So if you don't have heat with the engine being warm you do not have water flow. I would also look into the water pump, maybe the impeller has sheared off or is eroded beyond being useful in pumping water.

A simple check before tearing stuff apart would be to let the engine warm up and then touch the hoses going to the cab. If both are a lot colder to the touch than the cylinder head on the intake side you know that there is no flow.

Just my 2c

 

Moved to 1st gen forum.

Don't forget that the thermostat is required in order for the water to flow in the correct directions. Some people have had their problems get worse while running without the thermostat.

 

I see 3 problems.
1. I suspect that either the t-stat is stuck, or missing. You have to use the right thermostat. If you use an aftermarket t-stat, it'll work, but it'll cycle up and down, with the first cycle being unnervingly hot. The Cummins stat will cycle a little warm once then lock on to the operating temp.

If you haven't picked up on it yet, the thermostat has a valve disk on it that opens a bypass relief to the pump when it's closed. The wrong stat without that disk will likely cause overheat as much coolant bypasses the radiator.

2. The other problem (related to the heater) is that when you put coolant in the system, you have to "burp" it by removing the pipe plug in the head near the t-stat housing.

3. The third thing I see is this. The radiator holds about 8 quarts. The engine holds a similar amount. The burp bubble is about a quart. It looks like you're filling the engine, not burping it, and the radiator is completely plugged.

A fourth possibility is a bad water pump.
It ain't rocket science, and the wrenching isn't difficult either. The radiator comes out with 4 bolts and 3 hose clamps. T-stat housing is right on top. You don't even have to get down off your feet to work on it.

Most of the old copper radiators are beyond help. Best replacement I've found is the Mishimoto high performance aluminum radiator. For me it changed the routine of pulling the double through places like the MacDonald pass from gearing down and taking a break at the scenic outlook to let things cool off, to high gear floored throttle cruise through running about 210°

 

Tried your quick little flow test aplineRAM... Both hoses are about the same temperature as the cylinder head, indicating that there is flow. This is after I installed a new thermostat. Thanks for the info, very much appreciated

 

Awesome information j_martin. I removed the old thermostat early this morning and swapped in a new one. After taking the truck for a little ride, the lower radiator hose is warm to the touch, whereas the upper is not. Is this normal? The temp gauge still hovers to the right of center... But I am thinking I need a better gauge than the terrible factory one. What temps should I expect to see? I am in the process of removing the plug above the t-stat housing in order to burp the system - I didn't realize that this had to be done. It's in there pretty tight... Going to put some penetrating lubricant on it and work at loosening it up. Thanks so much for the help