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Discussion Starter #1
I've been fighting cooling issues with my 67 since I bought it nearly 10 months ago. It's a 468 with an 8-71 blower.
In short, after 10-15 minutes of driving, the temp heads north of 210 and won't come back down. I have to turn it off and try to hide it in the shade. This has kept me from driving it.
I've had it towed to a shop twice and, in addition to non-cooling related things, they've done the following:
- Replaced the old electric fan with a 'high CFM' electric fan
- Added a radiator shroud (Griffin radiator)
- Adjusted the timing
- Moved the coolant temp sensor to make sure the reading was accurate
- Performed a hydrocarbon test (all good)
- Tried a smaller belt on the water pump
- Tried three different thermostats

Basically, they're now saying that they're out of options and they can only assume that it has to do with the thinness of the cylinder walls / inability to dissipate heat. I asked them to double check the A/F, coolant mixture, water pump setup, etc. to make sure we've covered all the basics before doing something drastic.

I've read that the cylinder walls SHOULDN'T drive the overheating issue (maybe core shift?) but I don't have any other explanations. Any other opinions on what might be causing this?

THANKS!!

Mike
 

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Which fan do you have? What are you using to activate it? Have you verified the fan isn't blowing forward (wired backwards)? Which Griffin radiator are you using?
 

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It's a 468 with an 8-71 blower.

The above is the biggest reason it wants to run hot. Roots blowers add a lot of heat to the engine, but they are so cool.

Seriously, I was having trouble getting my new naturally aspirated BBC to stay cool and it has the big Griffin radiator, good water pump, big high cfm fans, and my cylinder walls are a almost a half inch thick (Dart Big M). The temperatures didn't seem to settle down until I got enough timing into the tune up at low rpm and low loads (high manifold vacuum). You may have a similar issues when you are not making boost, not enough timing. BBC's seem to crave lots of timing when they are not making much power. I have EFI, so I can do stuff with my ignition timing that you cannot do with a mechanical distributor.

Just to give you an idea of where I am at. When I am cruising at 1700 to 2000 or so rpm, at 20-to-21 inches of manifold vacuum, I have approximately 45 degrees of ignition timing. The temperature is running about 206 to 211 degrees with the sending unit in the head on the drivers side. If I moved it to the intake manifold up by the thermostat, it would probably read about 190 to 195 degrees. The engine is very happy and the plugs look great. Your results may vary, but I think that your ignition timing may have a lot to do with the problems you are having. I am not sure how much improvement you can make, if you have a mechanical distributor, you may not be able to get enough timing into the engine due to the limitations of the mechanical parts of the distributor before detonation becomes a problem somewhere in the tune up.
 

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Discussion Starter #5
Thanks, all!

Bryan - I've asked the shop to provide me the timing readings so I can see if they're off the mark (maybe they don't know what it should be...). They seem to think it's optimized.

Chris - i'm not sure which fan, I had two SPAL fans but they replaced them with something they said was higher flow. I can check the model on it and the radiator once I get it back. I can't say I sanity checked the fan direction, but I would like to think I would have noticed it after they replaced it :) In any event I will check it. The fan is ignition activated if that's what you're asking.

CamaroDude - what would removing the thermostat accomplish? Just curious...

Mike
 

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CamaroDude - what would removing the thermostat accomplish? Just curious...

Mike
I run mine without a thermostat. It runs cooler without it. Occasionally over heated when I ran it with a thermostat. Has not overheated since I removed it. I also tired Moroso water outlet restrictors in place of the thermostat, it ran still cooler without the thermostat than with the restrictors. Another thing that can help is a lot of initial advance.

I've heard good things about Evans Waterless Coolant but haven't tried it. It's pricey, especially with the coolant capacity of a big block..

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Brett - Leander, Texas 1969 SS396
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What type of block is it? Is it a Mark IV Iron block? Iron or aluminum heads? (sorry if you mentioned that-I re-read you post so fast the second time around looking for that info).

I built a Mark IV 454 with a 6-71 blower and one thing I did that helped tremendously is I drilled the holes into the block that caused the cooling to be in parallel as opposed to in series. Google "Parallel vs series cooling BBC"....

Then, my hedders would get really hot (500+ degrees). I went with 2" primaries and all of my cooling problems went away. I was also running a Griffin radiator but I did have an electric water pump.

The first block I bought wasn't going to work for my build.......all of the water passages around the cylinders had been filled with concrete. Did you check for that? haha!

 

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Discussion Starter #9
The shop called this morning and indicated the distributor was locked out and the timing was set at 37. They lowered it to 28 and still no difference in the heating levels of the car. There is no vacuum advance due to the distributor.

I asked them if they could unlock it / adjust the vacuum timing to see if that will make a difference in the temps, waiting on them to get back to me.

Suggestions/thoughts?
 

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A friend of mine went through this on a similar blown BBC. Found out the block was cemented after ruining a set of aluminum heads. After he replaced the block, no issues.
 

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The shop called this morning and indicated the distributor was locked out and the timing was set at 37. They lowered it to 28 and still no difference in the heating levels of the car. There is no vacuum advance due to the distributor.

I asked them if they could unlock it / adjust the vacuum timing to see if that will make a difference in the temps, waiting on them to get back to me.

Suggestions/thoughts?
As stated, the 37 degrees isn't going to cause an issue. You wanna raise the initial. I'm locked out at 36, don't run a vacuum advance, and have my initial timing set at 22 degrees. I run an MSD billet distributor and I used a custom bushing to get the initial timing up to 22 degrees.

Here's a bushing similar to the one I used..
Tuning MSD Distributors

Not saying this will cure your issue but it may help and is pretty inexpensive.


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Discussion Starter #13
Thanks Rick Ben.

Thanks Mark - I asked the shop to give this a shot. They are trying it and will update.

Mike
 

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What type of block is it? Is it a Mark IV Iron block? Iron or aluminum heads? (sorry if you mentioned that-I re-read you post so fast the second time around looking for that info).

I

Brett, Is that a torque strap I see? near the ps hoses?
 

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The shop called this morning and indicated the distributor was locked out and the timing was set at 37. They lowered it to 28 and still no difference in the heating levels of the car. There is no vacuum advance due to the distributor.

I asked them if they could unlock it / adjust the vacuum timing to see if that will make a difference in the temps, waiting on them to get back to me.

Suggestions/thoughts?
The change to 28 degrees is not going to help your overheating, 37 would be better for that problem as long as the engine doesn't detonate under boost, which is probably why they retarded the timing. They have to compromise because your distributor has no vacuum advance, you are really limited with mechanical advance only.

If it were me, I would start saving my money and convert to a programmable electronic ignition system or EFI. Then you could get the timing adjusted where in needs to be in every situation without so much compromise. With what you have now, there's not much you can do.
 

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Brett - Leander, Texas 1969 SS396
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Brett, Is that a torque strap I see? near the ps hoses?
As a matter of fact, yes. They were only a mock up though. I found some cool torque limiters that I was going to use instead. It was on the 72 Chevelle I built so I could sell and have enough to buy a Camaro. Good observation!

Brett.....
 

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Discussion Starter #17
Update from today - shop attempted lowering the initial timing, they also tried a restrictor plate (re: thermostat), and no luck.

One of the earlier questions was around the motor components; this is the list I was able to dig up from the previous owner:
- Aluminum heads, #3919842 with the rec port closed, chambered/flowed to 113CC
- Deck height is 9.780
- Scat crank 4340 4.00" bore and stroke
- JE Pistons, 7.8:1 compression
- Comp cam 637/637 L 310/320 D 114
- Scorpion rockers

At this point, the shop is suggesting taking the motor part to diagnose the issue. They're asking for $1K in labor. Reasonable? Unreasonable?

I guess we will tackle a new ignition as a part of the rebuild if we go that route...

Mike
 

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Is the bottom radiator hose collapsing while the engine is running? No mention of radiator hoses, so I thought I'd mention it.
 

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Discussion Starter #20
One other sanity check comment - just for fun, we cranked it and let it sit, just to see if it would overheat whether it was driving or sitting. It still got too hot :(

Mike
 
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