The Stovebolt Site Forums The Shop Area Engine Shop Radiator Cap for 1955 235 (Radiator - Harrison '49

I'm having some cooling issues with my 235. My engine was bored out .060 over prior to rebuiding and my stock temp gauge shows about 210 degrees after about a 5 mile drive. I've noticed that it "pukes" one time a little bit around the cap after a short run but then seems to settle down. What pressure radiator cap do I need? Should I be concerned about it running around 210-215 degrees? Would an external electric fan help with this? Any suggestions would be greatly appreciated!

with the stock 51 rad you should have a 4# cap, maybe 7# if the rad is mint ... the minor puke one time means you're filling it too full, should be down at least a couple inches when cold to allow for expansion warmed up .... stat should be a 185 or even 160, but yes you should be concerned about a 235 running 210*, and if it needs an electric fan, something's wrong, with the cooling system or the rebuild .... don't trust the gauge until you use a good infrared thermometer to check actual temp, at various points on the engine and rad - should find close to thermoatat temp at the stat housing, about the same at the inlet hose of the rad, about 40* less at the bottom of the rad

Bill

Bill.. thanks for the feedback. The stock radiator is actually a '49 and I'm sure I've been filling it too full based on what you've said. I'll get a 4# and 7# cap and try them both. Thermostat is new and 185 degree. I also agree that I probably shouldn't trust the original gauge. I know the speedometer is about 10 mph lower than it should be. Any ideas where I might find either a shop that has an infrared thermometer or where I might buy one? Should an optimum running temperature be around 195 degree? Appreciate all your help!

check around local auto parts places, they're commonly used by repair shops now .... failing that, don't let anyone catch you putting the candy or meat thermometer from the kitchen in the rad

with a 185 stat, the engine should be running 185, the 235's usually run cool, so the stat forces it up to it's temp, can't imagine one running much over stat rating - good idea to check new stats to be sure, not unusual to find defective ones - also make sure you don't have an air lock, fixed by drilling a small hole in the surround next to the opening bellows

Bill

Chevy Ky - My setup is similar to yours. I have a stock '49 radiator on a recently rebuilt '59 235. I'm using a 180F thermostat and a 7 psi cap. With this combination, the engine will run indefinitely at 185 degrees, even when it's 100F outside.

I would start by checking the size of your fan. About the time GM changed the 235 engine to full pressure (1954), they also increased the size of the fan. I'm told the pre-1954 fan is usually 16.5 inches in diameter. The fan on my '59 235 is 19-inches in diameter. This may not seem like a big difference, but a 19-inch fan pushes roughly 50% more air than a 16.5 inch fan at any given RPM. If you are using a smaller fan from an older 216 or early 235, it will probably have a hard time keeping your engine cool.

The larger fan also has a different bolt pattern than the smaller fan, so it's not a direct swap. I drilled new holes in my fan so that it would fit the bolt pattern on the short-shaft water pump. Good luck.

If you've checked all the other stuff, especially that the ignition timing isn't retarded causing overheating, It would be worth checking that the radiator hasn't become partially blocked inside after many years of use.

This problem often appears with a rebuilt motor because the extra power the new motor makes pushes more heat into the cooling system.

A good way to check for a partially blocked rad is to slowly bring the revs up on the motor with the rad cap off, you shouldn't see any real change in the water level in the header tank as the motor and water pump speed up if the radiator core is good.

Stuart.

Is five miles the extent that you have driven it? I am wondering if you still have air trapped inside. If you start the engine and the temperature goes beyond the thermostat setting, check the upper rad hose. If the rad hose is cool, the thermostat isn't opening because of an air pocket. What happens next is a void forms in the block and the expansion pushes the coolant up into the rad and out the cap. I have been through this with my 216. What I do when I initially fill it up is I wait until the fore mentioned happens and then I shut off the engine. Then I remove the heater hose on the thermostat housing, hot air belches out and as soon as coolant appears, I Push it back on. After a few minutes the thermostat opens and I can run the engine normally. If it were me, I would start off with a 160 thermostat until everything is resolved.

Thanks to all that have responded. Truckernix, yes
5 miles is the extent I have driven it. I have
both of the outlets plugged that normally go to
the heater as I haven't yet decided what I am going
to do in that regard.

It doesn't matter if you have them plugged, the point is that you can bleed the air out of the top one. It is directly under the thermostat. If you do have air in there you can do damage trying to run it that way.