engine overheats, upper radiator hose cold, thermostat works

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.

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.)

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?

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.

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.

Is it collapsing the bottom hose?

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?

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

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....

Water pump.

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.

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!

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

You already know the answer, the coolant is not circulating, correct?
Now get to work and fix it and let us know what you did please

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

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

Agreed TJP.

Just fixed a 440 that had a marine impeller on the water pump. The impeller was made to spin backwards. Double check the direction its facing. Here's a reverse one!

Take off the radiator cap and start the car and check for flow as it heats up. If the pump is working and the thermostat opens you'll be able to see it easily. If it works with cap off install cap and if flow stops through hose you have an air lock.

Looks just like the normal one I have

These are not my pictures of the one I fixed. One of these is a reverse pump for sure.

I would not count on them being reverse rotation or marine. https://board.moparts.org/ubbthread...-block-oem-water-pumps-for-426-hemi.html

Sniper -- T/Anks for that information about the spring in the lower hose... I have only found new hoses WITHOUT the internal spring... puzzled me, figured it was a cost factor for the aftermarket replacements.

I recently changed my lower hose (as it was slightly leaking at the water pump neck hose connection.... hose probably 30+ years old!)... and had some overheating issues afterwards... and excessively high radiator and hose pressure. So, after it wanted to explode upon eventually releasing the cap (couple days!), I then ran my engine without the cap, without a thermostat.. and eventually saw big bubbles... blurps... coming out of the radiator... I obviously had some air pockets. IF it made any difference, my radiator is a new aluminum Triple-Flow design from U.S. Radiator.... down-up- down.

I seen this only once, but I found a lower radiator hose was coming apart on the inside. The section that was separating, would act like a flap, and block off the incoming coolant, greatly restricting flow. Not likely your case, but like I say, it has happened once before...

It there is proper coolant flow through the engine prior to the stat opening, then the heater hoses and bypass hose should be getting hot.

If they’re not warming up fairly quickly, there is likely some sort of water pump problem.

Hi guys, I didn't get a chance to do the flow test last weekend as I had planned. But I will post a new message with what I find hopefully by this weekend.

I grabbed a new water pump from Napa just in case, since that's what my gut said even though it's not leaking as has been my previous experience with failing water pumps. It's promising to see other people have had the same issue and it's been with a non-pumping water pump, which makes total sense since I have a working thermostat yet no movement into the upper hose. And things were working fine in the system even without a hole drilled in the thermostat. Thanks for the inputs.

Back when I was in high school I had a '64 Valiant, 225, that developed an intermittent over heat issue.

Turned out that the factory fit plastic impeller was basically free on the pump shaft, but had a little grip, when it felt like messing with me, the impeller would shift just enough in the pump cavity to stop it, fan still turning happily, no belt squeal, but no circulation either.

This didn't happen all the time, but every once in a while I would look at the gauge and the needle would be heading for the high side.

I was so glad when they stopped using those damn plastic impellers ...

Well I put it back together without thermostat, and indeed the water pump was stirring things up in the radiator. I put a 1/8" hole in the thermostat, put it back in, added coolant mix burping it as I go. Started it up and it's running great. I think I must have been low on coolant and/or air pockets.

Good find, now go drive it in the heat slowly to make sure you fixed it
Let us know please

FWIW I put a Milodon HV pump on my car recently and it's reversed compared to the one I took off. I then compared the one I took off to two other old ones I had and they are all oriented the same way.

The Milodon part number was clearly marked for CW rotation. I got it from Mancini. https://www.manciniracing.com/brbhigvolwat.html

Myself, I would change that thermostat out just in case it's flaky. Cheap insurance IMO

Both of those pumps have the impeller blades at 90° to the centerline of the shaft. They would both perform equally whatever direction they spin. The orientation of the arms holding the impeller blades is irrelevant.

Thanks for the reply. I got a little paranoid because I had been reading a thread on the HAMB that talked about reversed water pumps on GM cars with serpentine systems, so I checked the description on Mancini's website before installing it.

The main difference I noted in the HV pump was longer blades and that plate welded behind them. Some of the old pumps had 6 blades, others had 8, I figure that is A/C vs non A/C.

Now I'm totally confused. Why would Mancini state CW rotation if there was no difference? I pulled many boat motors and there was definitely a difference between left and right rotation motors.

Have you never seen an incorrect description for a part before? Straight vane pumps don't care, especially if you have an anti-cavitation plate on it. Curved vanes do.

From Cardone.