Proper Operating Temperature for an L-79

[Seth G.]

I own a stock 66 L-79 which recently began to run hotter at approximately 210 degrees. While the owners manual describes this as a proper operating temperature, it typically had been running cooler. My anti-freeze was changed and the mix may too rich. Are coolants (eg. redline waterweter) alright to use in the aluminum radiator? Also, can anyone tell me if 210 is too high or acceptable, etc? Thanks

Seth

[Duke W.]

Re: Proper Operating Temperature for an L-79

Your engine should have a 180 degree thermostat, and it should run about there unless the engine is under heavy load in hot weather.

The first thing you should do is verify the temperature with an IR gun on the thermostat outlet or an accurate meat thermometer in the expansion tank. Also check that the initial, centrifugal, and vacuum advance are properly adjusted and performing to specification.

The engine should operate at a normal temperature with up to about 70 percent antifreeze. Verify that the fan clutch is operating. If you shut down the engine with the temperature over 180 the fan should offer much more resistance to hand turning than when it is cold.

Water wetter, high flow coolant pumps and other backyard fixes are just crutches that won't solve the problem. How old is your aluminum radiator? Could be it has developed enought deposit buildup to signficantly reduce heat transfer, which is often the reason for hot running.

If your cooling system is set up to OEM spec with OEM parts it will cool properly, but if something is degraded and out of spec it can run hot. You need to find the out of spec part or parts and replace them with OEM equivalent to return cooling system performance to design specification.

Duke

[Duke W.]

Re: Proper Operating Temperature for an L-79

Your engine should have a 180 degree thermostat, and it should run about there unless the engine is under heavy load in hot weather.

The first thing you should do is verify the temperature with an IR gun on the thermostat outlet or an accurate meat thermometer in the expansion tank. Also check that the initial, centrifugal, and vacuum advance are properly adjusted and performing to specification.

The engine should operate at a normal temperature with up to about 70 percent antifreeze. Verify that the fan clutch is operating. If you shut down the engine with the temperature over 180 the fan should offer much more resistance to hand turning than when it is cold.

Water wetter, high flow coolant pumps and other backyard fixes are just crutches that won't solve the problem. How old is your aluminum radiator? Could be it has developed enought deposit buildup to signficantly reduce heat transfer, which is often the reason for hot running.

If your cooling system is set up to OEM spec with OEM parts it will cool properly, but if something is degraded and out of spec it can run hot. You need to find the out of spec part or parts and replace them with OEM equivalent to return cooling system performance to design specification.

Duke

[Gary S.]

Re: Proper Operating Temperature for an L-79

Seth, my 66 L79 ran 200-210 on the highway until I replaced the original 34 year old aluminum radiator with a repro Harrison. Then it ran 180 regardless of the outside air temperature or the speed I was driving.
Gary

[Gary S.]

Re: Proper Operating Temperature for an L-79

Seth, my 66 L79 ran 200-210 on the highway until I replaced the original 34 year old aluminum radiator with a repro Harrison. Then it ran 180 regardless of the outside air temperature or the speed I was driving.
Gary

[Jack H.]

Re: Proper Operating Temperature for an L-79

When something changes BAMN, I begin by rounding up the 'usual suspects'.... Typically, scale in radiator doesn't turn on/off like a light bulb!

If coolant was changed and you're suddenly running hotter, do you have a pressure containment problem? This can be checked with appropriate shop monitoring tools (gauge installs in place of rad cap). Do you have a flakey rad cap? The same tool can check your cap with an adaptor. Do you have residue build-up in the radiator/expansion tank that's causing the rubber seal in the rad cap not to sit flush? Are there hose clamps that need to be tightened and/or are hoses cracked or micro cracked?

I'd start with the simple things and build up. If the system is marginally holding pressure, you can expect temp to elevate.... So start with SCIENCE and verify what's going on. What's the real coolant temperature of the system vs. what the guage in the cockpit says or 'thinks' it is? Is the cooling system holding pressure properly? Without answering these questions first you can spend a LOT of time/$$$ chasing squirrels....

[Jack H.]

Re: Proper Operating Temperature for an L-79

When something changes BAMN, I begin by rounding up the 'usual suspects'.... Typically, scale in radiator doesn't turn on/off like a light bulb!

If coolant was changed and you're suddenly running hotter, do you have a pressure containment problem? This can be checked with appropriate shop monitoring tools (gauge installs in place of rad cap). Do you have a flakey rad cap? The same tool can check your cap with an adaptor. Do you have residue build-up in the radiator/expansion tank that's causing the rubber seal in the rad cap not to sit flush? Are there hose clamps that need to be tightened and/or are hoses cracked or micro cracked?

I'd start with the simple things and build up. If the system is marginally holding pressure, you can expect temp to elevate.... So start with SCIENCE and verify what's going on. What's the real coolant temperature of the system vs. what the guage in the cockpit says or 'thinks' it is? Is the cooling system holding pressure properly? Without answering these questions first you can spend a LOT of time/$$$ chasing squirrels....

[Mike Arteaga]

Re: Proper Operating Temperature for an L-79

Seth, the bad news is you probably need a radiator. The good news is it completely takes care of the problem! I tried everything and finally spent the $700 and that took care of the problem. Go to Dewitts web site they have some interesting info on what happens to aluminum over time and why you need to stay with aluminum! dewitts@ismi.net They are great to deal with and a wealth of knowledge!! Good luck!! Mike PS It's nice to go for a drive and not worry about overheating!!

[Mike Arteaga]

Re: Proper Operating Temperature for an L-79

Seth, the bad news is you probably need a radiator. The good news is it completely takes care of the problem! I tried everything and finally spent the $700 and that took care of the problem. Go to Dewitts web site they have some interesting info on what happens to aluminum over time and why you need to stay with aluminum! dewitts@ismi.net They are great to deal with and a wealth of knowledge!! Good luck!! Mike PS It's nice to go for a drive and not worry about overheating!!