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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Apr 2025 Posts: 3 Moderated | | Moderated Joined: Apr 2025 Posts: 3 | Hello, I'm Rick Brown, new to Stovebolt and haven't done much more than oil changes for decades. I bought a 1950 3/4 ton Chevy truck with a 235 head on a 261 block. It has overheating problems, after reading many posts I know there could be a lot reasons for overheating with the main one being the proper holes weren't drilled in the 235 head when the engine was rebuilt. Is there a way to figure out if the holes where drilled without taking the head off? The temperature difference between the head and block averages around 16 degrees, i.e., 200 head and 184 block.
After reading about the 261 engine and its unique thermostat, I figured that maybe that could be part of my problem, so I ordered a 261 thermostat. The thermostat housing appears to be for a 235 thermostat, the 261 is larger. Will the 235/261 combination work properly without the 261 thermostat? Or do I need to find a 261 thermostat housing? If so, will it work properly on a 235 head?
Also I'm not confident the radiator and fans, original and added electric, are cooling effectively, average deference between top outlet and bottom inlet is about 4 degrees.
Thank you. | | | | | Joined: Dec 2002 Posts: 3,441 Moderator - The Electrical Bay | | Moderator - The Electrical Bay Joined: Dec 2002 Posts: 3,441 | Hi Rick. I moved this post to the Engine Shop.
Please make a NEW post in the welcome aboard area and tell us a little about your truck. And maybe post a couple pictures.
Another quality post.
Real Trucks Rattle
HELP! The Paranoids are after me!
| | | | | Joined: Feb 2004 Posts: 29,787 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,787 | The correct 261 bypass thermostat has been out of production for many years. There is an extra port on the 261 housing to route coolant back to the water pump during warmup that the original stat blocked off with a flap valve once it opened up fully. Once the engine reached full operating temperature, that setup became a moot point. The only way to determine if the bypass holes in the head have been drilled is to pull the head. They're there to improve coolant flow beside the three pairs of siamese-cast cylinders, so if they haven't been drilled, the block, not the head would be too hot. Unless the coolant is boiling out of the radiator, the engine IS NOT overheating. Your temp difference between block and head is completely normal. Top to bottom temp difference at the radiator should be 20-30 degrees F. at least. It looks like you need to install a bigger radiator, or do a good clean and flush on the one you have.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Apr 2025 Posts: 3 Moderated | | Moderated Joined: Apr 2025 Posts: 3 | That's a relief, thank you for your quick response Jerry! | | |
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