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engine overheats, upper radiator hose cold, thermostat works #3051862
06/19/22 10:55 PM
06/19/22 10:55 PM
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Rancho Cordova, CA
Exit1965 Offline OP
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Trying to track down a recent (didn't change anything) overheating problem on my 73 d200 with a 360.

When I start the engine from cold, it gets up to about 230 after roughly 6 minutes of idling or low rpm in park before I turned it off. The upper radiator hose never warmed up in that period of time. I took the thermostat out to test (and it was in plenty of water in the thermostat housing), and it's opening at 180 when I test it in a pan of water. The radiator is full, and I don't see any leaks. The thermostat, upper and lower radiator hoses are all fairly new (1-2 years), and it had always been running at normal (180ish) temperatures before the past couple of times I've driven it.

Does that indicate the water pump itself is bad? It seems like it's not pumping otherwise I think the upper hose would get hot at 180+ degrees (certainly by 220+), yet when I think of a "bad water pump" I usually think of leaking which I don't think it is.

Re: engine overheats, upper radiator hose cold, thermostat works [Re: Exit1965] #3051865
06/19/22 11:18 PM
06/19/22 11:18 PM
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So Near, Yet So Far
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Test: leave the t-stat out, fire up, see if water in radiator is flowing or static.
I'll assume static check of fan wobbling shows none, and no noise from water pump indicating breakage.
Fan clutch ? Direct drive fan ?
If no circulation, there's either a blockage or the pump isn't working.
Blockage could be anywhere in the system (upper or lower hose, pump, housing, block, heads.
Do you get any heat out of the heater ? (Not that it could cause that problem, but it'll be a secondary symptom.)

Re: engine overheats, upper radiator hose cold, thermostat works [Re: topside] #3051868
06/19/22 11:26 PM
06/19/22 11:26 PM
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Rancho Cordova, CA
Exit1965 Offline OP
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It's a direct drive fan. I didn't try a wobble check but will try that. There is some kinda rotational noise now that you mention it, though it's subtle and I haven't tried to pinpoint it. There is no heater on the truck anymore, so that outlet on the water pump is capped.

Thanks for the ideas. I'll see what it does without the thermostat in it tomorrow. Would I expect to see lots of activity in there if the pump was working OK?

Re: engine overheats, upper radiator hose cold, thermostat works [Re: Exit1965] #3051884
06/20/22 01:14 AM
06/20/22 01:14 AM
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I have seen water pump impelller come loose from the shaft.
Why do you think its overheating? Are you going by a gauge? I would install another mechanical gauge a rule that out.

Re: engine overheats, upper radiator hose cold, thermostat works [Re: MoparMike1974] #3051898
06/20/22 07:45 AM
06/20/22 07:45 AM
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How are you determining that it gets up to 230?

If the hose is cold it's not at 230, even if the thermostat didn't open the hose will warm up above ambient enough to feel.

Re: engine overheats, upper radiator hose cold, thermostat works [Re: Exit1965] #3051907
06/20/22 08:42 AM
06/20/22 08:42 AM
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W. Kentucky
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Is it collapsing the bottom hose?

Re: engine overheats, upper radiator hose cold, thermostat works [Re: Sniper] #3051912
06/20/22 08:55 AM
06/20/22 08:55 AM
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Rancho Cordova, CA
Exit1965 Offline OP
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Not collapsing the bottom hose as far as I can see.

The 230 is from the digital water temp gauge. In 90 degree f weather, it seems it would be unusual to run an engine for 5-7 minutes without reaching 180. At which point hot liquid should begin to flow into the upper radiator hose as long as the thermostat is working, which it is. I think that's why I'm not believing it's just a bad temperature reading.

Re: engine overheats, upper radiator hose cold, thermostat works [Re: Exit1965] #3051968
06/20/22 12:14 PM
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Originally Posted by Exit1965
Not collapsing the bottom hose as far as I can see.

The 230 is from the digital water temp gauge. In 90 degree f weather, it seems it would be unusual to run an engine for 5-7 minutes without reaching 180. At which point hot liquid should begin to flow into the upper radiator hose as long as the thermostat is working, which it is. I think that's why I'm not believing it's just a bad temperature reading.



Gauge senders go bad. I would verify the readings with an IR gun or similar. Harbor Freight has them for cheap.

Did you run it up to temp with the cap off an observe any water flow thru the radiator? Can you try this without a thermometer installed, to eliminate it?

Re: engine overheats, upper radiator hose cold, thermostat works [Re: Exit1965] #3051996
06/20/22 01:51 PM
06/20/22 01:51 PM
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Originally Posted by Exit1965
It's a direct drive fan. I didn't try a wobble check but will try that. There is some kinda rotational noise now that you mention it, though it's subtle and I haven't tried to pinpoint it. There is no heater on the truck anymore, so that outlet on the water pump is capped.

Thanks for the ideas. I'll see what it does without the thermostat in it tomorrow. Would I expect to see lots of activity in there if the pump was working OK?

You should see the same activity with the stat open and the engine at 2K or more RPM. If not I would suspect a slipping belt, Impeller not turning, (off the shaft, loose on the shaft or broken shaft) or a blockage. keep in mind the blockage can be a plugged radiator, collapsing lower hose, T'stat not opening or installed upside down. Something is keeping the water from flowing, the question is WHAT ? Keep us posted twocents beer

Re: engine overheats, upper radiator hose cold, thermostat works [Re: TJP] #3052069
06/20/22 06:27 PM
06/20/22 06:27 PM
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I had a similar problem with my 76 PowerWagon. It was the impeller shaft not spinning. New water pump fixed that and have not had a bit of trouble with it since. Also running a 360....

Re: engine overheats, upper radiator hose cold, thermostat works [Re: dssaa] #3052107
06/20/22 11:32 PM
06/20/22 11:32 PM
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Highland, MI.
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Water pump.


No Man With A Good Car Needs To Be Justified
Re: engine overheats, upper radiator hose cold, thermostat works [Re: Sunroofcuda] #3052122
06/21/22 06:24 AM
06/21/22 06:24 AM
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Quote
I took the thermostat out to test (and it was in plenty of water in the thermostat housing)


Does the t stat have a bleeder valve? If not it will trap air and cause the problem you experienced. This goes for all LA and magnum motors. If the t stat doesn't have the bleeder valve drill a small hole(3/16-1/8) in the flat part of the t stat. This will let the air out when you fill it. If it does have the bleeder valve i would say the water pump is not moving the water.

Re: engine overheats, upper radiator hose cold, thermostat works [Re: Moparite] #3052214
06/21/22 03:41 PM
06/21/22 03:41 PM
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NW Chicago suburban area
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I agree with the T-stat.. must have a bleeder hole of decent size (~1/8-3/16").. I recently experienced the same problem... had an air pocket blocking flow after I replaced a lower hose... they apparently don't make many new T-stats with the bleeder hole... they should!


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Re: engine overheats, upper radiator hose cold, thermostat works [Re: Mopar Mitch] #3052222
06/21/22 04:47 PM
06/21/22 04:47 PM
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A bleeder hole isn't really required for our old stuff. But if air pockets concern you the best way to fill the cooling system is the vacuum method. No air in the system at all if you do that, which is also the way the factory did it and the reason older cars had a spring in the lower hose.

I got a fairly cheap kit on Amazon, pumped my cooling system down to 23.5" and filled it with new coolant. Done. No air pockets, no burping the system.

https://board.moparts.org/ubbthread...1951-plymouth-cambridge.html#Post3043150

Re: engine overheats, upper radiator hose cold, thermostat works [Re: Exit1965] #3052241
06/21/22 08:02 PM
06/21/22 08:02 PM
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You already know the answer, the coolant is not circulating, correct? grin
Now get to work and fix it and let us know what you did please wrench up


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Re: engine overheats, upper radiator hose cold, thermostat works [Re: Cab_Burge] #3052246
06/21/22 08:19 PM
06/21/22 08:19 PM
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Three days from the most logical approach mentioned by Topside - check for coolant flow.

Still waiting, and waiting, and....

Last edited by Transman; 06/21/22 08:20 PM.
Re: engine overheats, upper radiator hose cold, thermostat works [Re: A727Tflite] #3052272
06/21/22 09:45 PM
06/21/22 09:45 PM
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Originally Posted by Transman
Three days from the most logical approach mentioned by Topside - check for coolant flow.

Still waiting, and waiting, and....

I'll politely disagree with it being the most logical approach as doing so may mask a partially blocked radiator that may show more flow without the T/ Stat restriction.
In my experience over the last 50 or so years, if increasing the RPM to 2-3K shows no flow one needs to investigate why. other causes are mentioned above.
I will agree with you on the waiting part beer

Re: engine overheats, upper radiator hose cold, thermostat works [Re: TJP] #3052279
06/21/22 10:08 PM
06/21/22 10:08 PM
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Originally Posted by TJP
Originally Posted by Transman
Three days from the most logical approach mentioned by Topside - check for coolant flow.

Still waiting, and waiting, and....

I'll politely disagree with it being the most logical approach as doing so may mask a partially blocked radiator that may show more flow without the T/ Stat restriction.
In my experience over the last 50 or so years, if increasing the RPM to 2-3K shows no flow one needs to investigate why. other causes are mentioned above.
I will agree with you on the waiting part beer


His first post - “ didn’t change anything” - now it over heats. Why would one assume anything is blocked.

Logically - pull the stat and see if you have flow. If nothing, first order of business is check the pump.

Re: engine overheats, upper radiator hose cold, thermostat works [Re: A727Tflite] #3052287
06/21/22 10:42 PM
06/21/22 10:42 PM
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Originally Posted by Transman
Originally Posted by TJP
Originally Posted by Transman
Three days from the
Quote
most logical approach mentioned by Topside - check for coolant flow.

Still waiting, and waiting, and....

I'll politely disagree with it being the most logical approach as doing so may mask a partially blocked radiator that may show more flow without the T/ Stat restriction.
In my experience over the last 50 or so years, if increasing the RPM to 2-3K shows no flow one needs to investigate why. other causes are mentioned above.
I will agree with you on the waiting part beer


His first post - “ didn’t change anything” - now it over heats. Why would one assume anything is blocked.

Logically - pull the stat and see if you have flow. If nothing, first order of business is check the pump.


In the same post he said I took the thermostat out to test (and it was in plenty of water in the thermostat housing), and it's opening at 180 when I test it in a pan of water.

Which is why i suggested increasing the RPM, However with a cold upper hose and a stat that tested OK, if the belts not slipping Likely the pump hub, shaft, or impeller.
We're wasting out time trying to help someone who's not responding so beer

Re: engine overheats, upper radiator hose cold, thermostat works [Re: TJP] #3052346
06/22/22 10:04 AM
06/22/22 10:04 AM
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Agreed TJP. up

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