Overheating

[kgrasso76]

I have a 1968 Corvair engine (110 hp) in my 1970's dune buggy. Driving it is no problem. However this last weekend I was in a parade and it overheated and quit running. Let cool for a couple hours and then it started right up and I drove it home. The air temp was about 85 degrees and it took approximately 15 minutes to cover 3 blocks in the parade. I do not have a temp gauge on the buggy so I do not know how hot it got. Do you think it was just too much idling or any idea's why it got so hot? It may have vapor locked. I am new to air cooled motors and carbs. I did switch it to an electric fuel pump and running unleaded gas. Anything I can do?

[bbodie52]

I have never experienced the Corvair engine overheating while it was idling. If it was vapor lock, vapor lock can come from different sources. Each carburetor should have a plastic insulator sandwiched between two gaskets at the base of each carburetor. This helps to isolate the carburetor body from the aluminum intake manifold, which can get fairly hot as a part of the aluminum cylinder head casting. Without the plastic insulators (which sometimes are omitted if the old insulators crack or break during removal) the gasoline in the carburetors can overheat and possibly boil within the carburetor body fuel passages. This would result in a vapor lock problem.

Your electric fuel pump should be physically located close to the fuel tank. Electric fuel pumps are better at pushing fuel than pulling it for long distances. The fuel pump inlet should be a close gravity feed from the gas tank, and the fuel pump outlet should pressurize the fuel line all the way to the engine. The metal fuel lines around the engine should not be physically touching the metal engine components. If the engine is idling for long periods the fuel in the line will be essentially stationary and could overheat if too much heat is transferred from the engine components to the steel fuel line.

In 1968-1969, the mechanical fuel pump outlet utilized a cross fitting that added a fuel return line all the way to the gas tank. This thinner line kept a small percentage of gasoline circulating through the fuel lines and back to the gas tank. Keeping the fuel in motion help to keep it in a liquid state and kept it at cooler temperatures to avoid vapor lock. A similar technique was used with 1962 and later turbocharged Corvair engines at the fuel filter in the engine compartment. The fuel filter included a fuel return line back to the gas tank to keep the fluid in motion. If you have eliminated the mechanical fuel pump and the associated fuel return line back to the tank that was a part of the 1968-1969 engine configuration, the fuel return line with not be a part of your system and the stationary gasoline in the fuel line could conceivably overheat and vaporize, which would starve the carburetors for gasoline. With long periods of idle, the gasoline in the float bowls could conceivably become exhausted and might not be replenished if the fuel had overheated and vaporized on its way from the electric fuel pump and fuel tank.

http://www.corvair.com/user-cgi/catalog ... IN&page=67

[kgrasso76]

Thanks for the info. I bought the buggy last fall, and this was one of the first times I actually used it. I located the fuel pump by the gas tank, however the fuel filter and pressure regulator are located in the back by the motor. I replaced the plastic gasket between the manifold and the carb, by I do not know if the return line is run to the tank. I will check this out.

[azdave]

Do you have a picture of the engine? Many people delete some ducting when they do a dune buggy install. We need to know how much of the original cooling system is in place. Does it still have the stock oil cooler? Is it blocked with debris? Have you looked under the cooling fan shroud for mouse nests and such that can be hidden and block the cooling air?

[kgrasso76]

It appears the return line for the fuel was cut and capped so the fuel would not be able to circulate. I had the shroud off recently, and replaced the oil cooler. I think that it vapor locked due to the inability to circulate the fuel.

[caraholic4life]

IF the Dune Buggy had been in storage or infrequently driven for a while prior to your purchase, there is a GOOD chance that there are remnants of Mouse Nests under the top shroud and between the cylinders.

If the lower shrouds are off the engine, poke a bright flashlight in the top shroud wherever you can and look to see if there is visible light from below.

If it is relatively easy for you to pull the carbs and top shroud. I would suggest taking the time to do it and get a good clear look at what is or is not there. It would be much less expensive and easier than any other diagnosis method I can think of. It could save a lot of time, money, and frustration.

I would also agree that the Electric Fuel Pump should be as close to the Gas Tank as possible. Mechanical pumps that were stock on the Corvair did a good job pulling the fuel but as mentioned already, Electric Pumps work best to push the fuel.