The Stovebolt Site Forums The Shop Area Engine Shop Just rebuilt 261 overheating

Ok , 1962 261 with 8 minutes of total running time with a 235 head drilled for steam holes.New short shaft water pump in the orginal postion. With 7 inch pulley. New old style four bladed fan. Lowered 1 inch New aluminum radiator. Removed thermostat and cap after second over heat. Cap off, at idle still over heats.No spring in lower hose. No Shroud. No gauge set up. throws a guyser. and dumps 1 3/4 gals at a time. One of my many Questions, When a bottom hose collapes is it just for a moment? Engine is in frame, Body off.Help!

There has been a lot of discussion here on the Bolt about overheating...have you read this thread "Engine getting too hot before thermostat opens"?

You need to run the thermostat, without it the water flows to fast through the radiator and it can't cool the water.

Is your engine to tight?

Does your T-stat have a 1/8" bleeder hole.

Is you radiator cap a pressurized cap? You need to run with a pressurized cap as it raises the boiling point.

Did you have an electric fan blowing in front of the radiator? With no sheet metal the original fan may not be pulling enough air through the radiator...

That's all I can think about now...others will chime in with their thoughts.

Mike B

When filling with water temporally remove the temp sender or the plug you have in its place. Make sure you fill the radiator until water comes out of the head before replugging. this bleeds all the air out.
I also question whether there is enough air flow through the radiator.
Retarded timing can make an engine run hot.
Thermostat removal causing overheating has been debunked many times. I never install a thermostat during break-in.

Another thing to consider is your pulley size on the water pump. 7 inches sounds big for a modern water pump. A large pulley would slow down flow in the engine.

Thanks, for all the suggestions. Is the engine to tight? Its just rebuilt, but it was ran in electrically for 30 minutes . Dave68 No, I did not bleed the sending unit, but I will. I have no electric fan attached. However, think Ill pick up a large box fan to see if that makes a difference. Pulley size I got the pulley and water pump from Patricks, so I feel pretty confident he sold me the right kit. Outside air temp was 35F yesterday. seem like there might have been a large air pocket after I removed the thermostat and cap the third boil over just pushed 1 3/4 gallons out water didnt seem that hot. Still wandering about hose collapsing as there is no spring. How many gallons does the system hold?

My freshly rebuilt 261 was overheating also. Long story short, my timing was off. I timed using a vacuum gauge and overheating stopped.
Good luck.
Joe

Thanks Joe, I think i didn't realize the value of a timed engine. I'll give it a try. thxs Greg

Sounds like a simple air pocket in the engine, fill with water only and install the thermostat once the water level is up to it. The lower hose should be fine, it hasn't run long enough to heat the hose or really start to draw in from the radiator. Is the hose stiff or really soft? Soft hose might need a spring inside if it becomes a issue.

For now, just get the air out and keep the radiator cool till you can be sure the timing and carb are set right. Once you are happy with the tune up, then look at the coolant system for any problems.

I don't know how you are checking the timing, but you should be able to set the timing almost dead on before you ever turn the engine over. If this is a new cam, you need to get this figured out before you ruin the cam, look up cam break in procedures on any cam manufacturers website. One of the points will be to have the timing set properly. Also removing the thermostat isn't necessary, (unless of course it is bad) be sure to bleed all the air from the system using the various methods described above. Keeping the thermostat in place should only be beneficial by letting the engine come up to proper operating temperature.

What does "ran in electrically" mean?
Jerry

Spun by an electric motor on a stand is my bet.

Really bad idea!
Jerry

"8 minutes of total running time" sort of contradicts the "ran in electrically for 30 minutes" - and what's the "total" mean, four 2 minute attempts? .... ambient temp near freezing .... seems spewing a couple gallons of cold/cool water wouldn't have anything to do with engine heat unless the stat was stuck closed [by ice?] and suddenly opened .... and what's it indicate when water "spews" when there's no thermostat and the rad cap is off so no heat pressure can build up? who rebuilt the engine?

Bill

Jerry;

Maybe a Spintron? Though that's pretty pricey for a Stovebolt rebuild.

SimS

Not very likely- - - -some rebuilders check a freshly-assembled engine for oil pressure, etc. by spinning the engine with an electric motor for a while to see if it burns a bearing or has a lube-related problem. Of course, it has the potential to destroy a new cam if it isn't done right, and it does nothing to show up cooling problems or do any dynamic loading of piston rings from combustion pressure for ring seating. Nothing beats a proper run-in at the right speed after doing a pre-start tuneup and monitoring all the vital signs during the run-in. A sloppy buildup or wrong run-in procedure is responsible for the vast majority of failures of newly-assembled engines.
Jerry

^^^ I agree. Why change a successful process?

SimS

It's called chasing the almighty dollar. A high-volume rebuilder that's putting out a hundred engines a day can hire some nose-picker from a temp labor service, pay him a few bucks above minimum wage, and teach him how to run a spin-test machine in a day or two if he's got more than three brain cells to rub together. It will catch the really badly-assembled ones- - - a rod bearing missing, etc. Then they replace the failed engines that got past the run-in during the 90-day warranty with another half-donkey rebuild. It's all about beating ther law of averages with barely-acceptable "rebuilt" engines.
Jerry

Anything new on the original problem?
Last post by OP was Tuesday morning.

My previous engine shop put a plug in the block where the water spicket should be. When I was finally able to drill out this plug since of course it didn't just come out, NO water came out with it. It took thick safety wire and lots of prodding to get the black gunk to finally break loose. I don't know if this would change the heating/cooling characteristics of the engine block to the degree it would matter, I am just offering this because I made the mistake of not removing the spicket and freeze plugs before having them do their cleaning on my first rebuild many years ago. I make sure this is done nowadays. There is a degree of looking out for yourself when taking your engine to a machine shop. I just didn't know!

I have heard of a lot of engines that were recently rebuilt that over heated because there wasn't enough clearance between the piston and the cylinder. It seems like no one measures any more. They just stuff the pistons in the holes and consider that a .030 over piston is gonna have to work in a .030 hole.

I haven't worked on a Chev in years, just GMC. But I assume they have a petcock right by the steering box like a GMC. I have pretty good luck cleaning blocks by turning them upside down and screwing a pressure washer fitting into the petcock hole. A pressure washer causes enough turbulence to knock a lot of crud loose. Casting sand sometimes even comes out. But I would suspect something else than to much crud in the block to overheat in just 8 minutes with no load.