I am looking to get two additional gauges to monitor the temps on my 337 ci flathead engine. One will be a more accurate Oil Pressure Gauge than stock. The second will be a temperature gauge. Should I go with an Oil Temp gauge or a Coolant Temp Gauge? They will be mounted on a panel below the dash - exact location not yet determined.

John
NNY

 

Moniter the coolant temperature. Use a 5psi radiator cap and use a 185 thermostat.

 

It may be a dumb question but, why is coolant temp more important than oil temp? Does the radiator heat up first, then the oil, the oil gets thin and oil pressure drops?

John
NNY

 

Your oil will be fine if your oil pressure is good (and you said you already planned for that gauge,) and if the coolant temperature is known to be ok. Certainly the oil temp is critical but the cylinder heads are where all the heat is generated so that will get hot first.

 

With a flathead the coolant temp is important, but only IMHO, where it boils. I think that the standard gauge is good enough for that. Ditto with the oil pressure, as the standard gauge is good enough also. The important thing would be to put real money into a radiator that can run a high pressure cap which will raise the boiling point up to the 250 degree area and allow you to get great cooling in high ambient temperatures. There is a new radiator cap that has a temperature gauge built in. You might need to use a mechanical coolant temp gauge that can handle higher temps than the stock gauge. You might want to monitor oil temps if you are running the engine hard, like with a lot of load. I monitor the automatic transmission temp with my truck. That is the only extra gauge I have had to use. I am using the old 56 stock gauges and they are reasonably accurate.

 

Good points but I don't know what the benefit of a higher pressure cap would be. The cooling system was designed for 4 psi operation, and (if in good condition) keeps the coolant well below the temps associated with that (about 224 at sea level). I don't know if the 337 had sealed bearing water pumps(?) but if it doesn't, higher pressure will just blow water past the seals. In general, high water temps are not good for flatheads.

It seems to me I have read that the 337's were tough on oil (high temps), while the 239's weren't. Not sure why 337's would be, maybe in hauling heavy loads, but it wouldn't do any good to know your temps are high unless you could do something about it! I don't see any way to fit a cooler.

 

You are missing the entire idea of high temperature livability. This is that the amount of cooling possible at high outside (ambient) temperatures is increased if the boiling point is raised. Secondly, the amount of pressure in the system depends on the temperature. In other words, if the engine is cool, the pressure built up in the system is low. What you are doing is protecting the engine by allowing it to live at higher temperatures in case they happen. You say a flathead does not like higher temperatures. Well in the first place this is a myth. We find that the flatheads are no different than any other engines. Most engines run best at about 240 degrees, which is where most competition engines are run. But what you need to take to heart is that flatheads are destroyed by boiling. This usually causes cracks around the valves. So the high temperature liviability is to prevent boiling, not raise the operating temperature. If you can still run the engine at 230 degrees you will drastically increase its cooling rate and minimize the chances of boiling.

The old water pumps can take pressure, and the ones built or rebuilt now have newer seals. The really old water pumps from the '20s and early 30's could not. 15PSI is not that much, but it drastically affects the boiling point of water. Also, most heating gets connected with high altitudes climbing grades with a load. At 6200 feet, the boiling point without any pressure is 187 degrees.

We are porting and building a lot of flatheads now, as they are very popular now with rod builders and we have had a big infusion of the French built flatheads (built for French Tanks) so there are lots of blocks and complete engines available right now. We are ready to race a '53 F-100 flathead at Bonneville in 2008. The main things that cause heating are boring the cylinders out, high power production (because you are cooling the exhaust port heat), high ambient temps, small radiator, low pressure cooling system.

Alan