48 Flathead overheats
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Mountain Pass
Joined: Jul 2001
Posts: 170
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From: Miles City
48 Flathead overheats
My friend has a 48 pickup with a stock flattie and trans. The radiator flow checked OK,its got r/b water pumps and new thermostats.AT 40MPH it will run warm but wont overheat but at 50MPH the temp doesnt stop climbing. I read something in a street rod mag a few years back about ignition timing and overheating on Flatties but cant remember specifics.Any body goy any ideas?Thanks.
Senior User
Joined: Jul 2001
Posts: 311
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From: Walla Walla USA
48 Flathead overheats
[font size="1" color="#FF0000"]LAST EDITED ON 20-Aug-01 AT 10:40 PM (EST)[/font][p]I have a 48 f-1 that also overheated a lot. I changed the thermostat and checked all the proper places........ It turned out to be the check valve in the exhaust manifold. These valves were put in place to automatically close when the engine was cold and then open once the engine was warm (Winter starting). But the valve gets stuck shut or the balance gets broken making it impossible to stay open. You have to take off the exhaust manifold...On my ford it is on the passenger side.....and either remove the check valve or jury rig the valve to stay open. You won't find any replacement parts for this, or atleast none that work correctly after you remove them from some old heap sitting around. They rust shut.......while you are at it....change any gaskets that might be leaking......Oh, never heard of the ignition timing...don't know why that would effect the overheating but might. If you find it to be let me know. jim
Senior User
Joined: Jul 2001
Posts: 311
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From: Walla Walla USA
48 Flathead overheats
Check the check valve......it is called a butterfly. I knew when I wrote the response yesterday that check valve didn't sound right. Same place, location and all, but call it a butterfly in the manifold. jim
Postmaster
Joined: Dec 1999
Posts: 2,813
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From: Connecticut
48 Flathead overheats
If you want to get technical, it's called a heat riser assembly, in Ford terminology. Yes they do get rusty. You can take the butterfly flap out and plug the hole in each side. I would definitely check the timing as they say. make sure it's dead on to specs. Check your mixture settings on the carb. Flatheads are noted for overheating.
New User
Joined: Sep 2001
Posts: 24
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From: Gulf Coast
48 Flathead overheats
What has this engine been overbored to? Anything above .060 can cause overheating, especially if the radiator has been recored and it was a lighter core than original (fewer passes and fins). Many of the "Modern" cores are very light in relation to the original style cores, just lift one that has been recored and then lift an original. BIG difference. Hope this helps.
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thendrix
1948 - 1956 F1, F100 & Larger F-Series Trucks
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