Overheating problem finally solved!

[Patrick H.]

Many of you may recall that I've mentioned an overheating problem with a 1972 350/200hp small block I've worked on. The car is quite original, but sat for 15+ years before I worked on it for the owner and got it back into running condition. One of the few problems we've had since it got back on the road is that it would overheat when driving through town or even sitting in his garage. I'm not talking about just a bit of a temp gauge spike or a coolant puke here. I'm talking it has cracked 2 exhaust manifolds, melted wires, melted 2 sets of windshield washer bottles and (rare) extensions, melted power steering hose and more. This engine got HOT!

When I initially worked on the car it got all new hoses, rebuilt water pump, block flushed, new radiator cap, and anything else. After the first year of problems the very old replacement radiator started leaking and the owner installed a brand new DeWitt correct repro radiator (he had at first wanted to see if the one in the car still worked). Despite this, it didn't change the condition at all. Last year right after Bloomington I drove over to his house and did more work to it and replaced damaged parts, but nothing seemed to help.

In September I then asked about a fan clutch replacement in this thread:
https://www.forums.ncrs.org/showthread.php?95842-Fan-Spacer-and-or-Fan-Clutch-substitute

I did not end up replacing the fan clutch because I tested it and it was obvious it was working.

Using various flow charts regarding overheating as well as discussions with Duke Williams and Bill Clupper I decided to see if the timing might be the problem. Now realize that the car was timed at factory specs, the vacuum advance system was working properly, and I thought that if they ran in 1972 like this then they should run just fine in 2013, correct? I sent the distributor to Bill and he verified that it was working properly with 15 degrees total centrifugal advance, and with a shimming of the end play and a lubrication job he sent it back. Based on his and Duke's comments as to what to try next I did two things. First, I changed the initial advance from 8 degrees BTDC to 20 degrees BTDC to give me 35 degrees total (20 + 15). Second, I changed the vacuum advance to a full time vacuum rather than only in 4th gear, which is what the TCS system does.

With these two changes I took the car out Saturday for a ride to warm it up, watched the temp, and then let it run for 15 minutes while it sat in the driveway. Meanwhile I changed the oil in my truck. Note that previously it would have been overheating and puking as soon as I had returned from a drive, much less after sitting running for 15 minutes. And here is what the temp gauge showed after 15 minutes of continued idling in the driveway (click on it for larger picture):

temp gauge.jpg
Needless to say this is all I could have hoped for, and the owner is thrilled.

I set the idle at 600, then bumped it up to 700 until I can replace the spark plug wires and get rid of an intermittent miss. Of note, it generally idles better, has stopped backfiring and the throttle response is much smoother and faster.

Thanks to Duke and Bill especially for their suggestions.
I never would have believed that timing - especially at factory specs - would have caused such a severe overheating problem.

Patrick

[Terry M.]

Re: Overheating problem finally solved!

Many of you may recall that I've mentioned an overheating problem with a 1972 350/200hp small block I've worked on. The car is quite original, but sat for 15+ years before I worked on it for the owner and got it back into running condition. One of the few problems we've had since it got back on the road is that it would overheat when driving through town or even sitting in his garage. I'm not talking about just a bit of a temp gauge spike or a coolant puke here. I'm talking it has cracked 2 exhaust manifolds, melted wires, melted 2 sets of windshield washer bottles and (rare) extensions, melted power steering hose and more. This engine got HOT!

When I initially worked on the car it got all new hoses, rebuilt water pump, block flushed, new radiator cap, and anything else. After the first year of problems the very old replacement radiator started leaking and the owner installed a brand new DeWitt correct repro radiator (he had at first wanted to see if the one in the car still worked). Despite this, it didn't change the condition at all. Last year right after Bloomington I drove over to his house and did more work to it and replaced damaged parts, but nothing seemed to help.

In September I then asked about a fan clutch replacement in this thread:
https://www.forums.ncrs.org/showthread.php?95842-Fan-Spacer-and-or-Fan-Clutch-substitute

I did not end up replacing the fan clutch because I tested it and it was obvious it was working.

Using various flow charts regarding overheating as well as discussions with Duke Williams and Bill Clupper I decided to see if the timing might be the problem. Now realize that the car was timed at factory specs, the vacuum advance system was working properly, and I thought that if they ran in 1972 like this then they should run just fine in 2013, correct? I sent the distributor to Bill and he verified that it was working properly with 15 degrees total centrifugal advance, and with a shimming of the end play and a lubrication job he sent it back. Based on his and Duke's comments as to what to try next I did two things. First, I changed the initial advance from 8 degrees BTDC to 20 degrees BTDC to give me 35 degrees total (20 + 15). Second, I changed the vacuum advance to a full time vacuum rather than only in 4th gear, which is what the TCS system does.

With these two changes I took the car out Saturday for a ride to warm it up, watched the temp, and then let it run for 15 minutes while it sat in the driveway. Meanwhile I changed the oil in my truck. Note that previously it would have been overheating and puking as soon as I had returned from a drive, much less after sitting running for 15 minutes. And here is what the temp gauge showed after 15 minutes of continued idling in the driveway (click on it for larger picture):

[ATTACH=CONFIG]46246[/ATTACH]
Needless to say this is all I could have hoped for, and the owner is thrilled.

I set the idle at 600, then bumped it up to 700 until I can replace the spark plug wires and get rid of an intermittent miss. Of note, it generally idles better, has stopped backfiring and the throttle response is much smoother and faster.

Thanks to Duke and Bill especially for their suggestions.
I never would have believed that timing - especially at factory specs - would have caused such a severe overheating problem.

Patrick

Patrick,
Since you have posted about the originality of this car repeatedly I am going to assUme it has the original distributor housing and intake manifold. Is there a chisel mark between the two? Has the cam or timing chain been changed? How does the chisel mark align with the old and new timing settings?

[Michael G.]

Re: Overheating problem finally solved!

Patrick, Thanks for the follow-up. Very interesting stuff. I can't help but think there might be an issue with the timing chain based on the reaction you get from that procedure. All's well that ends well. Thanks.

[Patrick H.]

Re: Overheating problem finally solved!

Patrick,
Since you have posted about the originality of this car repeatedly I am going to assUme it has the original distributor housing and intake manifold. Is there a chisel mark between the two? Has the cam or timing chain been changed? How does the chisel mark align with the old and new timing settings?

Initially I timed it using the mark you reference on the distributor and the intake, and it overheated with that combination (yes, I did verify it too). That's about as factory-correct as you can get. I use the same method with my own yellow 72.
I swapped the intake on the car last year with another correctly dated one because I thought the exhaust crossover might have a crack in it, allowing more heat into the engine. That didn't solve the problem, and I can't see a crack. We were looking for anything at that point.

Right now there's not much point comparing the original distributor mark to the replacement intake. I might make line with a marker so I know where my new timing mark is, but that's all.

Patrick

[Patrick H.]

Re: Overheating problem finally solved!

Patrick, Thanks for the follow-up. Very interesting stuff. I can't help but think there might be an issue with the timing chain based on the reaction you get from that procedure. All's well that ends well. Thanks.

I verified TDC using a piston stop and the harmonic damper mark, so at least that part is right on. Might the cam be off in its timing? Who knows.
Right now there are about 71000 miles on the car.

[Timothy B.]

Re: Overheating problem finally solved!

Patrick,

So you are saying 20* TOTAL IDLE TIMING, ( initial + vacuum advance)? I thought these cars had a temp sender that allowed vacuum advance at idle after the coolant temp rises to a certain point.

[Patrick H.]

Re: Overheating problem finally solved!

Patrick,

So you are saying 20* TOTAL IDLE TIMING, ( initial + vacuum advance)? I thought these cars had a temp sender that allowed vacuum advance at idle after the coolant temp rises to a certain point.

20 degrees initial, 35 total. Both the centrifugal and the vacuum coincidentally are 15 degrees each on this car.
Yes, they do have that temp sender and this one works when I test it. However, it doesn't work well enough to keep the car at proper operating temperature.

FYI, in my own car that temp sender doesn't kick on until the engine is definitely over the 210 mark. So, I don't think it would help keep it at 180 on a regular basis.

I'm not sure I'll keep it at 20 degrees initial advance in the long term, but it sure works well now.
I may try 16 degrees later this week and see how it goes, bringing it down bits at a time below that if the temp stays stable. No matter what I know it's on the right track.

Patrick

[Timothy B.]

Re: Overheating problem finally solved!

The reason I asked is because if your vacuum advance is operating with full time manifold vacuum like you report and 20* initial timing your engine is idling with 35* total idle timing.

If that's true, try the full time vacuum advance (15*) with 10 initial timing which will yield 25* idle timing and see if that is good at keeping idle temps down. After that, consider changing the distributor centrifugal advance curve to allow approx 26* all in at 3000 rpm. That along with the 10* initial will yield 36 WOT timing and with a fully functional vacuum advance total cruise timing could go as high as 51*.

With a 20* initial timing set point you may experence some slow cranking when the engine is hot that where the full time vacuum advance and approx 10* initial will help.

[Patrick H.]

Re: Overheating problem finally solved!

I will probably try a stepward decrease in timing to 14 then 12 and then 10, watching temps as I go. I did buy the advance spring kit from Accel in case I decide to start playing with that as well.

[Monte M.]

Re: Overheating problem finally solved!

Pat,

I am going through trying to find my TCS lead that plugs into the heat sensor in the head. From everything you have gone through, it sounds like I should just make it look right anyway. If the TCS is going to cause it to overheat anyway, I see no advantage in hooking it up.

Monte

[Patrick H.]

Re: Overheating problem finally solved!

Pat,

I am going through trying to find my TCS lead that plugs into the heat sensor in the head. From everything you have gone through, it sounds like I should just make it look right anyway. If the TCS is going to cause it to overheat anyway, I see no advantage in hooking it up.

Monte

I've toyed around with the idea of "gutting" the TCS solenoid that mounts onto the intake manifold and allowing for full time manifold vacuum. Note, though, that you may fail an NCRS Operations test doing this, and definitely would fail a PV test.

Patrick

[Joe L.]

Re: Overheating problem finally solved!

[QUOTE
I never would have believed that timing - especially at factory specs - would have caused such a severe overheating problem.

Patrick

[/QUOTE]

Patrick------


I totally agree. To wit: I believe you have a nearly identical 1972. I assume that your engine configuration/timing set-up is completely as-original. If so, how come your car doesn't overheat just like the other one did with stock, original set-up? There has to be more to it than this.

By the way, with the kind of overheating this car experienced as you described, he'll be lucky if the heads or block are not cracked.

[Patrick H.]

Re: Overheating problem finally solved!

I never would have believed that timing - especially at factory specs - would have caused such a severe overheating problem.

Patrick

Patrick------


I totally agree. To wit: I believe you have a nearly identical 1972. I assume that your engine configuration/timing set-up is completely as-original. If so, how come your car doesn't overheat just like the other one did with stock, original set-up? There has to be more to it than this.

By the way, with the kind of overheating this car experienced as you described, he'll be lucky if the heads or block are not cracked.

Joe,

That thought has occurred to me many times, that there may be a hidden crack. Now you can understand why I replaced the intake after having cracked two exhaust manifolds. It's the "hidden" exhaust passage.
FYI I think that the exhaust surface of the right side head is warped from all of this. I can't seem to get a planed exhaust manifold to seal anymore without a gasket.

And, I have no idea why the "twin" car I own doesn't do this. It's one of the reasons why timing never crossed my mind. But, with only 2 changes in timing (initial spec to 20 (at this moment) and converting to full time vacuum advance) the problem with his car is gone.
It will be interesting to see if the temp changes as I change the initial timing back towards 8 or 12 BTDC. Maybe the full vacuum advance will prove to be the only differing factor.

Patrick

[Terry M.]

Re: Overheating problem finally solved!

Joe,

That thought has occurred to me many times, that there may be a hidden crack. Now you can understand why I replaced the intake after having cracked two exhaust manifolds. It's the "hidden" exhaust passage.
FYI I think that the exhaust surface of the right side head is warped from all of this. I can't seem to get a planed exhaust manifold to seal anymore without a gasket.

And, I have no idea why the "twin" car I own doesn't do this. It's one of the reasons why timing never crossed my mind. But, with only 2 changes in timing (initial spec to 20 (at this moment) and converting to full time vacuum advance) the problem with his car is gone.
It will be interesting to see if the temp changes as I change the initial timing back towards 8 or 12 BTDC. Maybe the full vacuum advance will prove to be the only differing factor.

Patrick

But Patrick, thousands of these engines ran trouble free with ported vacuum and timing set at factory specifications. Something else is wrong and you are treating the symptom. Could the timing chain have skipped a tooth? Those nylon gears don't like to be without oil for a long time (or so I was told by a Powertrain Engineer).

[Joe L.]

Re: Overheating problem finally solved!

Joe,

That thought has occurred to me many times, that there may be a hidden crack. Now you can understand why I replaced the intake after having cracked two exhaust manifolds. It's the "hidden" exhaust passage.
FYI I think that the exhaust surface of the right side head is warped from all of this. I can't seem to get a planed exhaust manifold to seal anymore without a gasket.

And, I have no idea why the "twin" car I own doesn't do this. It's one of the reasons why timing never crossed my mind. But, with only 2 changes in timing (initial spec to 20 (at this moment) and converting to full time vacuum advance) the problem with his car is gone.
It will be interesting to see if the temp changes as I change the initial timing back towards 8 or 12 BTDC. Maybe the full vacuum advance will prove to be the only differing factor.

Patrick

Patrick------


The timing change might be "compensating" for the real cause of the overheating.