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Topic Review (Newest First)
10-12-2012 12:43 PM
Senior Chief
Radiator woes

Good afternoon guys,
Well I pulled both heads... good news - heads are okay, gaskets were fine, block is not cracked anywhere on either side. NO indication of water leaking into the block or oil pan.
Remember the water being lost was being forced out the overflow tube as I said in the begining. I have upped my timing and have talked to a radiator shop about getting the neck cut down to accomadate fifteen pound cap as that is about the only thing I know left to do.

10-08-2012 06:24 PM
John long I agree with Dave concerning a head gasket or cracked block causing an engine to run hot and it is possible for it to happen without the oil going to the crankcase. The thing that made me not suspect a head gasket or block is the fact that Jim indicated it was ok on a cool day. Generally the problem will exist at all temperatures if you have compression leaking into the cooling system. They make testers that check for carbon monoxide in cooling system. They go on the radiator cap. The ones I have seen have a blue liquid in them and as the engine heats up and the bubbles go through the tester the liquid will turn yellow if there is exhaust gas (carbon monoxide) present.

John L
10-08-2012 05:57 PM
Senior Chief Hey David, Thanks for jumping in. I considered the cracked block but have found no evidence of water in the oil. I am going to try advancing the timing and see what happens. If the problem persists then I will pull the right head and have a look-see. I have another block that is in good shape I pulled out of the car that was seized because of a blown head gasket I can swap out. I had it boiled and checked for cracks then put it out in my shed after coating every square inch with grease just in case.
After that there will be no more flathead engine if something happens to it. I will reluctantly pull it and drop in a 350 with 700R4 automatic transmission and call it done. I hate to consider having to do that but I will. As you say there are fewer people who know (I used to build these things in my sleep when I was a kid but have CRS disease after stroke during quadruple by-pass years ago) how to work on them. And of course like you and many other people have pointed out, easier getting parts, less cost involved etc. That 350 Chevy engine are a dime a dozen to find. As a matter of fact I know where two are right now I could have for practically nothing out of a friends garage.
10-08-2012 02:39 PM
Irelands child I've been watching your post - and think that you might just have a bigger problem - that of a cracked block. Flatheads with the siamesed exhaust where the two center cylinders have a single block port have ancient a history of cracking if you overheat. The fact that you are continually having to add water is often an indicator. What happens - the overheat condition, and it might only take once for it to happen - is that the exhaust valve seat will crack. This crack can go a couple of different directions, but the most common is into the cylinder wall. Here are some photos of cracks:: http://

These cracks can be fixed, but that Chevy belly button engine price starts to look good about that time.

Pull the head on the side that wiped out the temp sender and take a look - it only takes an hour or so, off and then back on (and I've even been known to reuse those head gaskets, especially if it was a copper one)

Flatheads are great nostalgia engines - unfortunately, have gotten way too expensive for parts as well as trying to find anyone that knows much about them

Dave W
10-08-2012 11:32 AM
John long Maybe an overdrive would be a good change for you. There is nothing fun about going down the road feeling like you are in second gear anyway.
10-08-2012 10:41 AM
Senior Chief I prefer the two lane drives. I don't like to drive at 70 preferring instead to drive around 60/65 alternating. The only time I run 70 is when I am following a group of fellow car enthusiests to a show. I ask before hand that we not travel above 65 and if they agree but ignore I only ride with their group once. I have been known to fall back to 65 and let them zoom off into the sunset.
I keep about six gallons of water in the trunk just in case it is needed but am tired of this.
The problem for me I guess is that most of my friends have cars with modern big and small block Chevy engines in them so they can't comprehend what I deal with. I hate driving Interstate unless I absolutely have to. But on the other hand one is more likely to get help on the interstates rather than the back roads.
This year when I drove down to Myrtle Beach from Gastonia, NC on the backroads by my lonesome and was perfectly content puttering along at 60 mph. I have come to the conclussion that I will never be able to run with the big dogs so I'll just stay on the porch when necessary.

Thanks John
10-07-2012 11:15 PM
John long It is typical of a flattie to run hotter at speed because of the exhaust port arrangement. Having an A/C system definitely stresses the system further. I notice mine will run 180 deg at 65 on two lane hwy on a 90 deg day. It will run 205 at the same speed on the same day on the interstate. The difference has to be the temperature of the air 12inches above the asphalt on that 5 lane super slab. Those conditions did not exist in 1951 and you could not go 70 mph for hours at a time.
It is also significant to note I am running a 5 speed with OD that drastically lowers my rpm,s

John L
10-07-2012 10:23 PM
Senior Chief Hey John,
When I first finished rebuilding the engine after having it boiled and checked for cracks etc. the engine ran pretty good. The temp never got above 190 on either gage. Then one hot summer while going to a show about fifty five miles from home (Carolina Hot 99 degrees) she over heated. I was running 65 on the Interstate. I pulled off found a place to let it cool down, refilled with water and was on my way seemingly with no further problems. The gage for the left bank pegged itself and destroyed the thing. On the way home I had to constantly stop and fill the radiator with water. I replaced gage, cleaned system, replaced both right and left water thermostats and added coolant.
Everything seemed fine as long as the ambiant temperature remained in the low 70's and if you didn't kick your speed up past 55. If it was a cool rainy day you could go up to 70 with no problems.
Around town no over heating problems at all. I thought I had the problem solved there for a while but I was in error.
I have the engine timed according to the specs but then in 1951 the car didn't have A/C, it wasn't 12 volt neg ground. It didn't have electric windows, electric doors etc. I have noticed that I can run the A/C around town but dare not on the open highway.
I was having so many issues with the car at one point I damn near ripped the flathead out and dropped in a Chevy engine that all my friends tried to talk me into in the first place. The only issue I have left is this damn overheating problem but you have given me renewed hope!

10-07-2012 05:54 PM
John long
Originally Posted by Senior Chief View Post
Thanks John! The fan was changed to a high output electric fan do you think that could be part of the problem? I have been running it for years with no problems until recently.

Jim, Are you saying that the engine did not used to run hot but now it does? If that is the case, something must have changed.

I run a '51 Merc engine that is pretty well built. It sits behind a stock '36 ford radiator which is not even pressurized. The only time this engine even thinks about getting hot is on the interstate when it is 90 deg or higher out. Under no circumstances does it run hot at idle or around town. As I said earlier, the timing needs to be right and it is imparative that the radiator is fully utilized. The factory shrouds or baffles need to be installed so the hot air can not recirculate through the radiator. I personally run a Cooling Components electric fan and shroud which assures air is being pulled through the entire radiator.

One other thing I do is run a small block Chevy distributor which has been machined and set up with the correct advance curve for the flathead. That way I don't have to deal with the totally inadequate ignition that the flatties were built with.

Are your problems occurring on the highway at speed or around town and idling?

John L
10-07-2012 04:49 PM
Senior Chief
Radiator woes

Thanks John! I thought retarding the timing was wrong. I recalled adjusting the timing up instead of down back in the 60's. The rust may be a factor here. Because I was overheating so much I stopped putting in antifreeze. It just so happens that I started cleaning out the cooling system by adding radiator flush to the system so it would be ready to drain and clean by the time I arrived home from the show she was in. I flushed it out pretty good last night but haven't added water back due to the fact I need to buy some antifreeze. The thermostats are new as I changed them thinking they might be part of the problem. No water in the oil so I doubt it is a blown headgasket. I have no idea the gear ratio as the one in the car is what Henry put in originally. The fan was changed to a high output electric fan do you think that could be part of the problem? I have been running it for years with no problems until recently.

10-07-2012 02:38 PM
John long Hey SC. DO NOT retard your timing. Just the opposite. The more advanced you set it the cooler it will run. The flathead exhaust passages go between the cylinders and through the water jackets. Retarded timing means that superheated exhaust is turning your cooling system into a blast furnace. In most cases the cooling issues with a flathead are at higher RPMs for this reason. The best solutions for engine heating are:

1 Timing as high as practical (this is imperative on a flathead)
2 All air dams and shrouding installed on car
3 A full radiator shroud
4 good tall gear ratio in rear end. (keeps RPMs down).

There are other possible issues. Lean fuel, rust in cooling system, collapsing heater hoses, blown head gasket, Bad thermostats, etc but the above are the most common. Good luck.

John L
10-07-2012 12:21 PM
Senior Chief
Over heating Flattie

I am having ocassional over heating problems with my flathead engine. If I drive the car when it is cool things seem to be better but if I drive in weather hotter than 76 degrees she wants to over-heat. Flathead Jack suggested years ago to do away with vacuum distributor and go with either electronic or dual point. I went with electronic. I still experience the ocassional over heating problem.
I was talking to a couple of old friends at a car show yesterday who suggested I retard the timeing by two degrees. Another said I should get a heavier duty radiator cap. I am running a seven pound one now with over flow bottle. Even the over flow bottle is over flowing. Since the neck for 51 Ford radiator is one inch deep one cannot find a cap heavier than seven pounds. I have been told I should get the radiator cut down to receive a 3/4 depth neck cap. Any suggestions?????

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