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I just finished replacing my hydralic lifters on my 52 250. During the project, in addition to replacing the lifters (which required pulling and replacing the head), I replaced the water pump (the old one showed some leakage around the weep hole), rebuilt the carb, R&R the heat riser assembly, and replaced the heater control valve at the firewall. I did not replace the thermostat - had a new one, just forgot I pulled the radiator but did not have it serviced, i did a simply flow test and it emptied quickly. I did repaint it with radiator paint, just the top, not the fins.

Since reassembly, the car has run hot. I have dialed in the carb (which still runs just a little rich) and the timing, and that has helped. The car never ran hot before.

I live by the ocean, and the temp stays around 70 - 75 degrees, so overheating really should not be an issue.

Now, it will idle in my garage forever with no problem, but after about 15 minutes on the road, basically on the highway at 55 mph, the gauge slowly creeps over toward hot. I haven't run it long enough to get it there, but I am pretty sure it will go fully to hot with a little more time. My hand held laser thermometer shows about 210 degrees across the heads at that point, a little lower in the main block and the radiator at about 180. Previously, I never saw the gauge get above the center. In the garage at idle, even idling for a long period, it only gets to about 170 at the block, the radiator only about 140.

I did not flush or back flush the engine.

The water passages in the head were very clean.

I think my next step is to replace the T-stat, or maybe run without one for a while and see if that helps. If not, I'll run something through the system and backflush it - which is another reason I might leave the T-stat out for a while.

I am wondering if the pump could be under-performing. Is there any way to test for this? As a last resort, I can put the old one back on and see if that solves the problem.

I am running with the heater closed, but I don't think this should make any real difference.

I don't really want to tear into this again, so any thoughts would be appreciated.

With pump fixed, maybe it sucks the inlet hose so restricting flow when warm?

Usually when these problems arise it is usually suggested that it is timing or maybe the vacuum advance not working.....

Your symptoms are suggestive of inadequate radiator flow rate or possibly a restrictive muffler or constricted exhaust.

If something goes wrong after a repair, then something was most likely improperly repaired/replaced. This is troubleshooting 101 stuff(NASA). "defects on or about a change"

Three things come to mind; thermostat put in backward, air pocket in the block or head - inadequate fill, problems with the pump rebuild - like a piece of gasket fell taking off into a passage or other simple things like a clearance issue. The way water flows, pumps have to have a certain casing clearance to function otherwise cavitation or other issues develop.

Heat transfer is controlled in autos by air exchange. Simply, a pound of water(~pint) holds one BTU per degree, but it takes ~50 ft3 (4X the mass) of air at a lower temperature to absorb that amount of heat. This ones before my time, but don't these '41 cars have the thermostatic grill louvers? If equipped, maybe that's not functioning/hooked up as well.

Then next level falls on the water side; fouling, flow, and surface area.
Then the combustion side; temp, heat generation.

Owen D - your observation on exhaust restriction is interesting, and not in a good way. When rebuilding the heat riser, I was unable to get the weight for the heat riser to be at 6 o'clock when opened. Best I could do was about 11 0'clock closed (or diverted to the intake) and about 7/8 o'clock opened, or undiverted. I posted a subject on that a few weeks ago. It is now exactly as the one in my '41 (which is to say that undiverted is around 7/8 o'clock), which seems to work. There are a few pictures, but I don't know how to cross reference them here. When this (overheating) started, I removed the spring from the post, allowing the weight to fall to full open at all times. I don't see how this is restrictive, but it is an area that I believe is different from before. I think the shaft is slighty different in the rebuild kit, but maybe I put the flap in totally wrong. Can you look at that post and see if it looks OK to your eye? I show pix of both diverted and undiverted.

If anyone has a good picture or diagram of how this (heat riser) goes together, I would really appreciate it.

Arthur C - I am not sure I follow your comment here. Are you thinking the water pump is pulling hard enough to collapse the intake hose? I will look at this when hot, but the system is a 7 lb system and generally the hoses are under pressure when everything gets hot. The bottom hose is new (actually all are) . The only sign I get of collapse is when the car cools down, the top hose shows a small amount of contraction, i think from the displacement as the water contracts to normal temp. This was also the case before the rebuild.

PTV - The engine is timed at 6 BTC, per the manual, and I can see a good amount of additional advance when I accelerate. Also, the timing is confirmed by my vacuum gauge and i have good power throughout the driving curve, so I believe it is right on. It is a great suggestion, I have a Plymouth flathead that is very sensitive to timing and will run hot when it is off, so this is an area I have looked at closely. The vacuum unit is the same as when I began.

Jim - yes, I am assuming that I did something wrong or caused an issue, so I am trying to think through what the potential causes are. I can eventually get all the way back to the head gasket, but I don't think that is where the issue is. I'll try to easy stuff first - flushing the system, thermostat and then I'll put the old water pump back on. I was not aware it was going bad until I removed it and saw traces of rust from the weep hole and on the balancer. But you are right - I need to think through everything I did as the problem did not exist before. BTW - this is my '52 I am working on - no louvers.

This gives me a few new tings to look at. Thanks to all for taking the time to help.

I was at the garage this AM and let the car idle quite a while to get to temperature. I used a radiator thermometer and my hand help temp gauge.

One thing I noticed is that the car comes up to temperature very slowly, and the radiator seems to keep pace. Even before the thermostat should open - say 145 - 150 degrees, the radiator is at a similar temp - maybe a little less, but not appreciably.

I noted no difference when the car finally hit 160 degrees, and the top radiator hose was probably only about 110 degrees. I could not feel and water running through, but the radiator was at similar temp. I could not see water moving in the radiator as the thermostat opens, which I assume I would, but the water does churn (and gets heat from somewhere).

Finally got to 180 degrees and saw the same situation. The upper hose never got very hot, but the radiator did get to about 170.

I am assuming the radiator is getting heat exchange through the lower hose, but even at 180, the lower hose, the lower part of the radiator and the pump itself are all only around 150 degrees. The top is hotter.

I do not know what temp the thermostat is, but it is the older style with the bug spring. I do have a 160 degree one to install.

The exhaust manifolds would reach around 380 degrees, but the intake remained fairly cool at around 130 or so.

Just a thought, have you re-torqued the head since it was replaced?

Tom, I have re-torqued the head several times now. The last Time required very little torquing, the first time (which was only after letting it get up to temperature for a while in the garage) quite a bit. I am not really certain how often I should do this, but my sense is until it doesn't need it an longer. The torque is not high, I think it was 60 lbs.

Sounds like you've removed head torque as an issue. I was having overheating problems last fall. Turned out to be a bad head gasket that was allowing blow by between several cylinders. I'm not sure if a compression check would have identified this.