Overheating BBC 468 Pro Street Willy's Coupe

[Keith Morganstein]

A drawing helps. And I'm going to correct myself. There is 17* between the radiator outlet and the cylinder block.

image.jpg

With 17* deltaT one can deduce that coolant is not flowing well in the block area. Even when you had the external radiator connected, I'd expect that part of the block was running much hotter.

I'm don't know what temps look like with the wrong head gaskets, or mismatch heads.

[topradman]

Gauge reads zero, attach air line ( our shop air is at 165 psi to run big sandblasters & torches in addition to normal shop air equipment. Large rad shop ) and run up regulator to 100 psi on inlet pressure. 6 cylinders are at 0% leak, 1 is at 13%, one is at 7%.

[Keith Morganstein]

Gauge reads zero, attach air line ( our shop air is at 165 psi to run big sandblasters & torches in addition to normal shop air equipment. Large rad shop ) and run up regulator to 100 psi on inlet pressure. 6 cylinders are at 0% leak, 1 is at 13%, one is at 7%.

If the gauge reads 0, that is a 100% leak.

I.e. If you put 100 psi in and the gauge reads 90 psi, that would show 10% leak.

[Keith Morganstein]

If this is indeed what you are seeing, you have a very sick engine (needs major repair) in that customers car.

Just to be sure, the leak down test is being performed on the compression stroke (with both valves closed)?
I use a long breaker bar to hold the engine against the air pressure. Sometimes rotating the engine until it's up against the air pressure and seeing how high the leak down gauge will stabilize.

[topradman]

If this is indeed what you are seeing, you have a very sick engine (needs major repair) in that customers car.

Just to be sure, the leak down test is being performed on the compression stroke (with both valves closed)?
I use a long breaker bar to hold the engine against the air pressure. Sometimes rotating the engine until it's up against the air pressure and seeing how high the leak down gauge will stabilize.

Cylinder Info as follows:

[topradman]

I can tell you this... There is NO way leak down is at "0" when air leak is audible. So..... reread the instructions for both the Mac and the Snapon and both say to hook it up and set air pressure to 100 psi. I believe this is incorrect whether their instructions say it or not. I believe the unit should be preset to 100 psi before attaching to the cylinder hose. We actually got into an argument over this in the shop today. Only makes sense that if you set the pressure gauge to 100 psi as directed while you are already hooked up to a leaking cylinder ( as MadBill said, pretty impossible to find a "zero leak" cylinder, new or other wise, zero gap ring or not ) you would have to compensate with the regulator to get to 100 psi as directions state, which would understate the leak down percentage value.

This should probably be a poll.
Anyway, that being said, I think you can safely add about 4% to each of the cylinder leak values that I have posted.

[pamotorman]

how much water pressure is the pump building in the water jacket ? you need 30 to 50 pounds to make sure all the voids are filled.

Is that even possible with an electric water pump? Typical systems on most bbc vehicle applications have always been 13-15 psi cap. I realize that there is also pressure created from resistance in the system against water movement but I don't think that kind of pressure is even possible in a typical GM, Chrysler, Ford typical ohv engine is it??

the 13-15 is in the rad not the block and heads. that is why you need a restrictor in the coolant outlet in the intake manifold.

[topradman]

how much water pressure is the pump building in the water jacket ? you need 30 to 50 pounds to make sure all the voids are filled.

Is that even possible with an electric water pump? Typical systems on most bbc vehicle applications have always been 13-15 psi cap. I realize that there is also pressure created from resistance in the system against water movement but I don't think that kind of pressure is even possible in a typical GM, Chrysler, Ford typical ohv engine is it??

the 13-15 is in the rad not the block and heads. that is why you need a restrictor in the coolant outlet in the intake manifold.

[Keith Morganstein]

I can tell you this... There is NO way leak down is at "0" when air leak is audible. So..... reread the instructions for both the Mac and the Snapon and both say to hook it up and set air pressure to 100 psi. I believe this is incorrect whether their instructions say it or not. I believe the unit should be preset to 100 psi before attaching to the cylinder hose. We actually got into an argument over this in the shop today. Only makes sense that if you set the pressure gauge to 100 psi as directed while you are already hooked up to a leaking cylinder ( as MadBill said, pretty impossible to find a "zero leak" cylinder, new or other wise, zero gap ring or not ) you would have to compensate with the regulator to get to 100 psi as directions state, which would understate the leak down percentage value.

This should probably be a poll.
Anyway, that being said, I think you can safely add about 4% to each of the cylinder leak values that I have posted.

You preset to 100 psi before connecting to the cylinder.

[Keith Morganstein]

It's a (popular) myth that restricting flow makes the system cool better. Something about slowing the coolant flow lets the coolant pick up more heat. It's just not true, more flow moves more heat. (And less flow moves less heat). That's why we look for flow problems when there is high temp differential.

As far as pressure, yes there is the system pressure of the cap. There will still be pressure differential in the system. There is a suction side and a pressure side of the pump... Where there is restriction to flow, pressure differential will increase across the restriction.

[geraldtson]

Wow,from leakdown test readings i'm probably wrong on this just the first thing came to mind i'm wondering if you've got some serious ring butting going on in some of those cylinders,maybe both compression rings even? That would sure explain the overheating issues. Good luck!!

[geraldtson]

Looking at leak down test serious ring butting would explain abnormal good numbers on leakdown while at same time show slightly lower numbers on compression due to scratched up cylinders walls and overheating issues from butted up ring drag. You said it was a low mile motor, no telling what kind of piston ring pack (gap or lack of). Plugs maybe would tell you something.It should be hard to start (drag) turn over. Anyways take a look and hope you get it figured out. Hopefully i'm way of on this for you're sake. Good Luck!!

[topradman]

It's a (popular) myth that restricting flow makes the system cool better. Something about slowing the coolant flow lets the coolant pick up more heat. It's just not true, more flow moves more heat. (And less flow moves less heat). That's why we look for flow problems when there is high temp differential.

As far as pressure, yes there is the system pressure of the cap. There will still be pressure differential in the system. There is a suction side and a pressure side of the pump... Where there is restriction to flow, pressure differential will increase across the restriction.

Ok, got pressure differentials and was pretty much concerned about how low they are based on a few previous comments to this post. So, contacted Meziere and bounced this scenario and the gathered data so far, especially pressure differentials. Their tech, "Jerry" says as far as the overall pressure being low, this is not a problem. I also let him know we are not running a thermostat or a restrictor and he says this is fine, that we want max flow, period. I also let him know we had 1 3/4" engine water outlet, radiator inlet & outlet & water pump inlet. He has no problem with this arrangement either.
He also assured me that they have this pump out there on a lot of big block chevys on the street having no cooling issues.

[pamotorman]

when I started racing BBC in 1966 we had heating problems and the people at GM racing told me to check the internal pressure in the block and heads. the pressure was low because of water pump cavitation at high RPMs so removing every other fin from the water pump Impeller raised the pressure in the block and it cured the heating problem.

[topradman]

when I started racing BBC in 1966 we had heating problems and the people at GM racing told me to check the internal pressure in the block and heads. the pressure was low because of water pump cavitation at high RPMs so removing every other fin from the water pump Impeller raised the pressure in the block and it cured the heating problem.

That makes very good sense. My problem comes in that I have doubts as to the ability of a Meziere 55 gpm pump to cavitate since it is electric. It is not rpm sensitive.

I think what you would have experienced with your bbc is that once a pump cavitated from high rpm, it had vapor it was trying to move inside the pump itself. I feel like removing every other blade on the impeller actually slowed the movement of coolant but the desired result you got was that is was no longer cavitating ( beating the crap out of the coolant ), not that it raised pressure in the block.

Does that make sense or am I way off here?