P12 Overheats...but Only With The Hood On...long Post

[rpmgarage]

Comments and advice welcome...frequent reader...rare that I post or comment...

I have a 1941 P12 engine and transmission in a 1936 Dodge d2 Touring Sedan. Rebuilt in 1988 with 0.020 overbore. Just changed the water pump and all hoses, new 160 thermo, new radiator cap (original style from Bernbaums), and tune up.

During the water pump change, I did not pull the Welsh plugs...I did have the radiator hot tanked. I also flushed, in every direction possible, the engine block and the heater core. I used a garden hose with about 60psi from a 3/4" feed line and used soapy water. The water tube in the block looked to be in excellent condition and I was easily able to run a smaller hose at least 18" into the tube. There was virtually no sludge and the water was quickly running clear enough that it looked like you could drink it. I then flushed in the reverse direction from the water pump opening in the block. I did this twice in each direction...again, the water was clear and coming out with great force...virtually no sludge.

After completing the reinstalls, I drove the car for over 120 miles in stop and go traffic (East TN in August...90+ with unbelievable humidity) over the next three days. The car barely got over 180 on a reliable mechanical gauge. The car even idled in the sun for at least 30 minutes without a hiccup.

All of this occurred while running without the hood on. Speeds ranged from 30 mph in city driving to 55 mph for a13 mile stretch of hilly highway. The longest continuous trip without shutting the engine off was easily over 1 hour.

After returning home and cooling down each time, I verified the coolant level (although I did forget and put in a 50/50 mix) to let the car get in its happy place.

I then put the hood back on to drive the car to a show. My trip was to be a total of 70 miles one way with the middle 20 miles on the interstate (55-60 mph). Most of the trip is hilly with speeds in the 45mph continuous range and under moderate to fairly heavy load.

The first 30 miles was trouble free, though the gauge climbed to 190+ on the steepest hills.

I stopped to fill the fuel tank just before getting on the interstate (17.9 mpg, by the way). While sitting at the station, I noticed that the gauge eased up to almost 205.

I then got on the interstate...max speed for any duration was under 60, with most at a continuous 55. Within 7 miles, the gauge was at 225. I stopped to eat a bite and let her cool off. She spit out about 2 cups of antifreeze. Starting back, she was under 180 on the gauge. Within 5 miles, she was back over 225.

Stopped again...cooled again...then made it off the interstate onto 35 mph city roads. She just kept getting hotter and hotter. When I heard her hiss, I pulled into a parking lot...she boiled almost 3 gallons out the overflow tube. I sat for an hour to let her cool enough to touch the head and water neck before refilling. This time, I filled her at 70/30. Within 5 miles, she overheated again...pegged the gauge...and spit up her hissy when I stopped at the show.

I will digress and wait for your help...and it will be appreciated.

Mike

[Don Coatney]

Fan belt intact and adjusted correctly? Lower radiator hose collapsing? Thermostat sticking in the closed position?

[Dave72dt]

Did it run cool before the water pump change? Before the thermostat change? If all was good before, one of the parts replaced is the problem.

[rpmgarage]

Don...are you in Pigeon Forge for The Shades? The car is there...would love to meet you tomorrow. Fan of your posts.

The previous water pump failed. The car was not running a thermostat at that time. The 120 mile plus, no issue, three day testing revealed a proper functioning thermo. No issues with hose collapse or flex. New thermo opening and closing, controlling properly. Fan belt is new and adjusted properly.

The car was overheating on long trips before the water pump went out...I had never driven it with the hood off back then though.

Again, the only real difference after the repair came when I put the hood back on. I am planning to trailer the car back home and remove the hood again for continued testing.

One item that I have not checked is the heat riser...though it was always in the vertical position before and never closed.

I did all the work myself, so I know the guy who did the work.

[Don Coatney]

Not in Pigeon Forge. Perhaps next year.

[rpmgarage]

Okay. I live 20 miles NW of Knoxville.

I will monitor the comments here, though I may not be able to reply or a couple of days.

[rpmgarage]

I have checked previous overheating threads and have found no specific reference.

Honestly, I do not know if the problem existed prior to the water pump going out. All of my trips were shorter and in much cooler weather. I had no issues then...if anything, the car ran too cool (no thermostat may have contributed to that in the cooler weather). So, I do not want to assume that the overheating NOW was or was not already an issue previously.

It reminds me of a 34 Ford with a flathead V-8 that I had. I bought it without a hood...drove it all spring and summer that way with no issues. Found a hood at a swap meet...you guessed it...overheated on the first trip. I never found the problem in that instance either. I drove it without the hood and sold it before I learned what caused the issue. The guy I sold it to said, "Yep...I'll just drive it without the hood and not worry about it."

I missed a learning opportunity right there...and now I need that info! Hate when I do that.

I want to sell this 36 to help finance building a Pilot House truck with a Cummins...but I don't want to miss the learning opportunity a second time.

[Don Coatney]

Is your engine setup for an internal or external thermostat by pass system?

 

I dont think a stuck heat riser would cause the overheating issues you have.

[chopt50wgn]

Since the motor is building excess heat, the hood is acting like the top of an oven. The heat being generated has no where to go so the motor is absorbing more heat.

 

[rpmgarage]

The bypass is external.

The "oven lid" makes complete sense...but where should I look to resolve the problem? I don't mind driving with the hood off...but the new owner may not see it that way.

[squirebill]

Search this Forum for "antfreeze".  Seems antifreeze causes engine to run hotter.  Might have to reduce your ratio of antifreeze to H2O.  Interesting test might be to drain antifreeze mixture...fill with just water and run/test drive again with hood on.

[Plymouthy Adams]

trust me he has a problem if his antifreeze mixture is doing as claimed..something is wrong....first and most simplest is the ignition timing...is it set proper?  Second the coolant is either not passing through the radiator due to internal restriction thus keeping the hot liquid in the block to get even hotter or he is not passing enough air over the skin of the radiator due to blockage of the fins/honeycomb or the air flow at speed has found  less restrictive path around the radiator..are your radiator side panels in place along with hood to radiator seal and did the temp lower by running the heater in the car on high fan high heat? and has the cooling system been properly cleaned of late, sediments removed from the lower part of the block by pulling the freeze plugs and cleaning and is the distribution tube working correctly.. shoot the head front to read and look for abnormal temp differences with a digital infrared thermometer..the coolant could also not be passing through the block correctly..if moving too fast it will not pick up the heat to carry to the radiator..if too slow it will hit saturation in the block to the point that the radiator is not effective in its removal of heat.. lastly he could well have a leaking head gasket

 

each of these scenarios can be easily checked and tested there are a number of checks that one can do...have you followed the step by step in the shop manual?

 

increase in temp up grades and heavy loads is normal but should not overheat and burp..sitting at the gas pump fueling up the block temp will rise and is normal as the water in the block is getting saturated but will immediately start to cool when the engine is started or vehicle attains road speed

Edited September 6, 2013 by Plymouthy Adams

[Don Coatney]

The car left the factory with an engine hood and did not overheat. The car left the factory with alcohol based antifreeze and I am sure it later was converted to glycol based antifreeze and it did not overheat. I suspect you have severe blockage in the coolant circulation system or your water pump has failed.

 

In my daily driver F-150 I once started the engine (when I was 500 miles away from home) and heard a clunk. As soon as I turned the steering wheel I noticed that I had no power steering. Suspected the surpentine belt had failed but an underhood inspection showed the belt intact and working correctly. What I found was the power steering pump shaft broke allowing the pump pulley to spin but the pump would not do any work. My point being that even though your water pump belt is turning your pump may not be pumping.

[TodFitch]

If the only change between overheating and not is putting the hood on, then air flow through the radiator would be my suspect. On the early to mid 1930s a lot of the air was to exit through the hood louvers and or louvers into the front wheel wells. Those haven't been blocked off have they?

[Dave72dt]

Here's a possibility that I don't know if it's physically possible to do.  Is the thermostat in upside down?  I'm starting to think about the possibility of a blown head gasket.

Edited September 6, 2013 by Dave72dt

[1941Rick]

Just because you boiled the rad does not mean it is clean inside. It sounds like you still have a problem with the rad. Look to see if there is any way hot air pulled by the fan can recirculate to the front. If the air loops around nothing you do will help other than remove the hood.

I

[martybose]

Just because you boiled the rad does not mean it is clean inside. It sounds like you still have a problem with the rad. Look to see if there is any way hot air pulled by the fan can recirculate to the front. If the air loops around nothing you do will help other than remove the hood.

This brings an interesting question to mind.  Do the early cars have a rubber barrier above the radiator that seals to the hood the way my 47 does?  If it doesn't, putting on the hood could redirect hot air to the front of the radiator.

 

Marty

[rpmgarage]

Thanks to everyone for their input.

Here are my responses, not in order: the radiator does not have an upper "seal" of any kind to seal to he grill surround. It does seal down the sides with the mounting tabs. The thermostat cannot be put in upside down because the housing would not seal to the block...it is installed properly and functioned as designed for three days plus of driving after doing all the above-stated work.

There is a sinle row of unblocked louvers on each side of the hood. They are from the factory and are punched so as to extract heat down the sides, not deliver fresh air from the front...which they would do poorly.

I started the car this morning at the Shades...idled for 40 mins plus...thermo opened and closed (verified by watching gauge and checking upper hose for pressure when thermo opened)...temp stayed below 180 the entire time...did not hiss or boil when shut off...temp climbed to about 195 while cooling...

Let her cool for 30 mins...took her for a drive in heavy, slow traffic (stop and go...10mph)...she overheated within the 5 mile loop...pegged the gauge again...spit out a gallon upon parking.

I believe Tod and others may be onto something...hot tanking the rad would not guarantee flow of AIR through passages...even though the water is flowing...there may be no AIR going over it...I can't perform too many more roadside tests up here...

I am thinking about doing the paper test where I see if it will hold against the rad from fan vac...

[rpmgarage]

I forgot to bring my digital thermo...will bring it back tomorrow and check all the usual spots...I will report back with the findings.

I don't believe in throwing parts at the problem, but could someone recommend a quality radiator...part number, company, etc. I will not sell the car until it teaches me something...

Remember...41 P12 in a 36 D2...would like a direct fit without any fab work...thanks...

[rpmgarage]

here are a couple of pics...

[rpmgarage]

well...maybe not...apparently I can't upload pics from an iPad2? Let me know the trick if I am missing something...

[desoto1939]

If your engine has the petcock on the dizzy side of the block open this to see if you get any water flow.  There still might be crud inthe block.  you might have to stick a hard metal rod into the opening to  free up any blockage.

 

I still think you might have crud in the block and might have to pullthe welch plugs or other wise known a freeze plugs. I also wondering if you might have an air bubble in the block.

 

rich hartung

desoto1939@aol.com

[1941Rick]

I used an aluminum rad from Performance Cooling. Never overheats even in 100 plus heat. Make sure you tell them it is for a 1948 Ply. Also give them the measurements of the old one. Otherwise you will end up with a rad 1/2 the size.

Boiling a rad should clean it externally. Its internally that is the problem

[rpmgarage]

The fan is stock...4 blade. The petcock is on the distributor side...I will check for flow later this evening as I am away from the car at this time.

I did not pull the Welsh/freeze plugs due to seeing the cleanliness of the flush water from the block and the heater core.

I have not started the car back again...it is 92 degrees right now...I plan to wait until evening before looking any further into it.

There are no signs of water in the oil dipstick or any foaming on the breather tube. There was no odor of antifreeze. I cannot due a pressure test on the cylinders until I get the car home...maybe more than a week from now.

As for an air pocket in the system...I filled the radiator above the water neck first, then let atmosphere adjust it with the thermo and housing off. Then I topped off the block to the brim before adding the thermo and housing. I also filled above the thermo outlet to the top of the outlet before adding the upper hose and continuing to fill the radiator.

I filled the radiator just to where it was visible. I then idled the car until the thermo opened...seeing the bubbling in the neck with the cap off. I let the car cool completely...added more mixture until I could see it again...let it bubble after thermo opened again. This time, it did not drop any. There was a total of roughly 4 gallons added to the system...about 2 in the block and 2 in the rad.

Drove the car in heat of the day for three days...120 miles plus...not so much as a burp and the water level did not drop. The car ran continuously for almost 1 1/2 hours at one point...all with the hood off. Temps never got above 195 mark, even upon parking and cooling. Thermo operated as gauge would rise up above 180 or so, then drop back almost to 150 or just above. It seems that any air pocket would have become apparent during that time...

Now...since it boiled out so much, there might be an air pocket NOW...but I don't see there having been any air pockets before this problem. Same way with the thermostat...does it seem likely that it would operate great for 3 days from purchase...then lock closed? Maybe so...but it's a NAPA piece...so I would really not expect it.

I have not ran with the heater on yet...will this evening. However, car will be sitting still for testing for two days...if I move it,I will lose my parking spot and do not have my trailer here in case of a break down. Will the heater on test help when the car is sitting still?

There is a gap of about 3" between the top/upper front of the rad and the grill shell...no seal...the hood sits flush on the grill shell...no weatherstripping or welt on the front section. Sides of the grill shell bolt to sides of the rad...there are holes in the mounting bracket that air can get through...no rubber seals...But, to be honest, I don't remember any of the 30 plus pre-1950 cars that I have owned having a "sealed" radiator mounting system...definitely nothing like my Buick Roadmaster or my F350 has...

[Scruffy49]

Maybe a silly question... did you use the "either/or" generic waterpump? Double check that the plate is the right way, I think the thread is on the truck side...

 

You are in TN, in the hills, in summer. Pull the stat out. I'm in the TN lowlands by the MS River, and most of my equipment I've pulled them out and left them out. Been getting a lot of bad parts new in the box from NAPA, John Deere, and other sources lately. All made in France, Mexico or Brazil.