BB Cooling Problem

[Louis C.]

Problem: I have a 1966 425 hp 427 Roadster, restored to NCRS specifications. When I drive the car on the highway (3:70 gear) the temperature climbs to 230-240, after fifteen or so miles. However, if while at 65mph I push in the clutch and idle the motor coasting down to 50 then accelerating back to 65 (time after time), the motor cools down to an acceptable temperature (210). It seems to me that the cooling system is insufficient to cool the motor under a load.

Around town it doesn't seem to be a problem. Unless stuck in traffic, typical of a BB?

The motor was built with flat tops and a slightly larger that stock cam. Timing is set by seat of the pants, due to the cam change. It starts well hot or cold, doesn't ping and is responsive. I could spend an hour describing the the various efforts I have taken to get this thing cooled down..... Rather, I will list my efforts: * Calibrated the temperature sender to the gage. * Roded the original radiator out. * Rebuilt water pump. * Has correct/original pulleys. * New belts/tight. * New Hoses. * Oliva rebuilt fan clutch. Tight! * Correct fan and shroud. * No power options. ie: air, A.I.R., PS. Just a water pump and alternator.

Other factors: * Motor is .060 * 3247 Carb is jetted stock. * Has side exhaust. * 50/50 coolant. Even tried Water Wetter. * Starting car in sunny south Florida at 100 degrees!

I feel like the one thing I have over looked for a long time is the thermostat. A recent conversation with a friend led me to take a closer look at it. It seems the installed thermostat flows considerably more coolant than a newly purchased one. Contrary to what I expected to find. Perhaps too much?

Any clues? Anybody?

[Chuck G.]

Re: BB Cooling Problem

You mentioned that the timing was set by the "seat of the pants" method. A car with the initial timing set too retarded will run hot. Also, a car which has problems with either the vacuum or centrifugal advance mechanisms not advancing the timing under power will allow the car to run retarded "at speed". Either of these cases could be making your car run hot. Check both the vacuum and centrifugal advances and check the initial timing. If your advance mechanisms both check out OK, try bumping up the timing. Hope this helps. Chuck

[Chuck G.]

Re: BB Cooling Problem

You mentioned that the timing was set by the "seat of the pants" method. A car with the initial timing set too retarded will run hot. Also, a car which has problems with either the vacuum or centrifugal advance mechanisms not advancing the timing under power will allow the car to run retarded "at speed". Either of these cases could be making your car run hot. Check both the vacuum and centrifugal advances and check the initial timing. If your advance mechanisms both check out OK, try bumping up the timing. Hope this helps. Chuck

[Louis C.]

Re: BB Cooling Problem

How can I be certain that the vacuum advance is correct for the application, and if it is functioning correctly.

[Louis C.]

Re: BB Cooling Problem

How can I be certain that the vacuum advance is correct for the application, and if it is functioning correctly.

[Tom B.]

Re: BB Cooling Problem

Chip,

I'll make several suggestions. The first is to go to the Archives and research this under, "cooling", "over-heating", and the posts that I made for "68 Aluminum Heads". There is a ton of information there that most everyone at the Discussion Board went through with me a couple months ago to get my 68 L89 cooled down. It will also cover alot of "periferal" stuff that I asked questions about (like timing, distributor, etc).

Second, what you're experiencing is fairly "usual". The point I'm at with my cooling system is that it reaches 205-210 for stop and go in-town driving, and 210-215 on the highway (I have 4.11 rear gears, at that). Your clutch fan is working properly. In town it is running to keep your engine where it is. On the highway it is correctly shutting down which is why you see the increase in temp.

All small items like foam around the radiator, etc, are there for a purpose: to help "inch" the temperature down. I would suggest you see what you can do for more air-flow through the radiator, as well as using the tip George Daina gave me for removing my front license plate assembly. I got an additional 5 to 10 degrees just out of that. Also, I have been told from another reliable source that the high highway temp is also due to the coolant passing through the radiator too fast and not getting a chance to cool off enough. I'm still researching that one, though. Hope some of this gets you pointed in the right direction. Tom #24014

[Tom B.]

Re: BB Cooling Problem

Chip,

I'll make several suggestions. The first is to go to the Archives and research this under, "cooling", "over-heating", and the posts that I made for "68 Aluminum Heads". There is a ton of information there that most everyone at the Discussion Board went through with me a couple months ago to get my 68 L89 cooled down. It will also cover alot of "periferal" stuff that I asked questions about (like timing, distributor, etc).

Second, what you're experiencing is fairly "usual". The point I'm at with my cooling system is that it reaches 205-210 for stop and go in-town driving, and 210-215 on the highway (I have 4.11 rear gears, at that). Your clutch fan is working properly. In town it is running to keep your engine where it is. On the highway it is correctly shutting down which is why you see the increase in temp.

All small items like foam around the radiator, etc, are there for a purpose: to help "inch" the temperature down. I would suggest you see what you can do for more air-flow through the radiator, as well as using the tip George Daina gave me for removing my front license plate assembly. I got an additional 5 to 10 degrees just out of that. Also, I have been told from another reliable source that the high highway temp is also due to the coolant passing through the radiator too fast and not getting a chance to cool off enough. I'm still researching that one, though. Hope some of this gets you pointed in the right direction. Tom #24014

[Bill W.]

Re: BB Cooling Problem

Chip, If you are using a GM vacuum can, there is a five digit number stamped into the metal near the body. The first three numbers relate to it's GM part number, the last two numbers tell you the degrees of advance it will provide. Usually 10 to 20 degrees. So, if you have inital timing set @ 10 degrees BTDC and your vacuum advance is stamped "10", you should have around 20 degrees showing with a timing light. To check that your "can" is working, watch your timing while you disconnect the vacuum going to it, timing should fall back to a lower mark and the idle speed should drop.

The amount of centriful advance built into your engine and the manifold vacuum needed to apply full vacuum advance at the "can" may make it somewhat confusing. The main thing is to have a correct vacuum can that works, and set the initial timing correctly. All this may or may not be part of your trouble, but these things need to be checked and eliminated as possible causes. Bill

[Bill W.]

Re: BB Cooling Problem

Chip, If you are using a GM vacuum can, there is a five digit number stamped into the metal near the body. The first three numbers relate to it's GM part number, the last two numbers tell you the degrees of advance it will provide. Usually 10 to 20 degrees. So, if you have inital timing set @ 10 degrees BTDC and your vacuum advance is stamped "10", you should have around 20 degrees showing with a timing light. To check that your "can" is working, watch your timing while you disconnect the vacuum going to it, timing should fall back to a lower mark and the idle speed should drop.

The amount of centriful advance built into your engine and the manifold vacuum needed to apply full vacuum advance at the "can" may make it somewhat confusing. The main thing is to have a correct vacuum can that works, and set the initial timing correctly. All this may or may not be part of your trouble, but these things need to be checked and eliminated as possible causes. Bill

[Tom B.]

Bill & Chip: Agreed

Bill and Chip,

Bill, I agree. And I didn't want to discourage you, Chip, from eliminating ANYTHING. There is a huge amount of small things that will affect the cooling/system. The experience that I just went through showed me that it was no ONE big culprit but rather alot of small, seemingly "insignificant" things that ALL added up to the "big picture". Keep eliminating/improving each individual item. Tom #24014

[Tom B.]

Bill & Chip: Agreed

Bill and Chip,

Bill, I agree. And I didn't want to discourage you, Chip, from eliminating ANYTHING. There is a huge amount of small things that will affect the cooling/system. The experience that I just went through showed me that it was no ONE big culprit but rather alot of small, seemingly "insignificant" things that ALL added up to the "big picture". Keep eliminating/improving each individual item. Tom #24014

[Jack H.]

Re: BB Cooling Problem

I'd be looking at radiator from both an air and coolant flow view. Telltale is problems appear when on the road under max convection air flow. Just getting rad internals 'bored' for free coolant flow doesn't guarantee the radiator is working at peak efficiency.

Bent fins, missing/ineffective air dams and the toll of internal wear will exact a toll. There's no easy fix but to take 'em one at a time and work the issues. Few rad shops sit down and straighten fins when they re-work a core....

[Jack H.]

Re: BB Cooling Problem

I'd be looking at radiator from both an air and coolant flow view. Telltale is problems appear when on the road under max convection air flow. Just getting rad internals 'bored' for free coolant flow doesn't guarantee the radiator is working at peak efficiency.

Bent fins, missing/ineffective air dams and the toll of internal wear will exact a toll. There's no easy fix but to take 'em one at a time and work the issues. Few rad shops sit down and straighten fins when they re-work a core....

[G B.]

A simple experiment

Take your thermostat completely out and go for a drive. You may be surprised at the difference it makes. The faster water circulates in your cooling system, the cooler your car will run. The old "water moving too fast through the radiator" myth lives on, but it doesn't make any sense if you think in heat transfer terms.

A high flow water pump helps too. I get them from Stewart Components.

[G B.]

A simple experiment

Take your thermostat completely out and go for a drive. You may be surprised at the difference it makes. The faster water circulates in your cooling system, the cooler your car will run. The old "water moving too fast through the radiator" myth lives on, but it doesn't make any sense if you think in heat transfer terms.

A high flow water pump helps too. I get them from Stewart Components.