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pebo va · 03-28-2020, 03:20 PM

Last fall I had a 1936 flathead rebuilt stock by an experienced engine machine shop. It has run hot since it was installed. Sometimes it overheats in 3 miles and sometimes it will run 1-2 hours before overheating. It starts up easily, runs strong with good power just as it should. But when steam comes out the radiator cap I need to add 1-2 gallons of water to bring the level up. It is not running out the overflow and there are no thermostats. When the radiator is full the water moves nicely as seen at the cap. When overheated and steaming I can hear gurgling and boiling noises. The radiator has been flow tested twice. All good. The water pumps are news Fryers. The distributor is correctly timed. I have changed the head gaskets twice. No help. It appears that somewhere internally the water jacket is leaking into the exhaust system. I added a bottle of Moroso's Ceramic block seal: no help. On my last road test last week on a 55 degree day, I ran at 35-55 MPH over country roads and at about 90 minutes it started steaming. While running, I then measure the temperature at various points with a laser gun. Aluminum heads on both sides 148-150 degrees.Lower hoses about 160. Water pumps 206 and 204. Front of the block 204. Top tank on radiator 204. Exhaust manifold 290 and 300.
Before I go to the trouble of pulling the engine is there something I am missing?

03-28-2020, 03:20 PM	#1
pebo va Member Join Date: May 2010 Posts: 62	Overheating Flathead Last fall I had a 1936 flathead rebuilt stock by an experienced engine machine shop. It has run hot since it was installed. Sometimes it overheats in 3 miles and sometimes it will run 1-2 hours before overheating. It starts up easily, runs strong with good power just as it should. But when steam comes out the radiator cap I need to add 1-2 gallons of water to bring the level up. It is not running out the overflow and there are no thermostats. When the radiator is full the water moves nicely as seen at the cap. When overheated and steaming I can hear gurgling and boiling noises. The radiator has been flow tested twice. All good. The water pumps are news Fryers. The distributor is correctly timed. I have changed the head gaskets twice. No help. It appears that somewhere internally the water jacket is leaking into the exhaust system. I added a bottle of Moroso's Ceramic block seal: no help. On my last road test last week on a 55 degree day, I ran at 35-55 MPH over country roads and at about 90 minutes it started steaming. While running, I then measure the temperature at various points with a laser gun. Aluminum heads on both sides 148-150 degrees.Lower hoses about 160. Water pumps 206 and 204. Front of the block 204. Top tank on radiator 204. Exhaust manifold 290 and 300. Before I go to the trouble of pulling the engine is there something I am missing?