After a full 3 years this month, I finally "finished" my ground-up frame-off restoration and rebuild of a 1971 Cutlass convertible. When I bought it, the car wasn't running and had a Chevy 5.7 Vortec that was a botched install. I pulled that out and picked up a core 1972 Rocket 350 and TH-350 from Olds442Redberet (Tom) along with a lot of other parts over the past several years. The motor was completely disassembled and sent off to a local machine shop that I trust (neighbor) and they went through everything. The block was checked for alignment, bored 0.030 over, and machine honed. The crank was polished (no turning needed). Everything was tanked and magnafluxed. The heads had new cuts on the valves and seats, and new hardened exhaust seats were put in. The block and heads were decked, and push rod clearances were checked in a mock-up assembly.

I replaced the pistons with Speed-Pro flat-tops and the cam is a 260 degree hydraulic from Comp. The rotating assembly was completely balanced.

I'm using a factory 4-bbl manifold and rebuilt Quadrajet. The points distributor is being used as a trigger for an MSD box and coil. I did NOT block off the exhaust crossover on the manifold and am trying to use the stove choke assembly. The exhaust is the original cast logs with brand new dual pipes and factory-quiet mufflers.

THE PROBLEM: OVERHEATING - BADLY

I'm using a salvaged radiator that came out of another Cutlass and had it tanked and pressure tested before installing. The motor gradually heats up to critical temps and eventually overwhelms the pressure cap, dumping water into the overflow tank pretty violently.

I've checked the timing and it's dead on 10 degrees advanced (w/o vacuum advance connected) and the fuel/air seems to be close enough to not be causing this.

It's a brand new water pump and thermostat with the factory flex-fan that was on the original A/C equipped motor.

The air coming off of the radiator is like a blast furnace. I had a hard time getting my hand in front of the carb to turn the mixture screws.

Could it be that the radiator is too small? I'm in the process of checking everything but, since I'm new to Oldsmobiles, I don't know if there is something different about the cooling system that I'm not doing right.

Thoughts?

Bill

 

nice car, there are special procedures to bleeding air out of the system after overhaul. one includes putting the front of the car on ramps so the radiator is the highest point in the system and the air bleeds out. check youtube or the internet. on a fresh build, I would leave the thermostat out during cam break-in. fan shrouds, proper fan-to-radiator clearance, making sure the lower radiator hose doesn't collapse when revving, are all factors. good luck

 

Ordinarily, I'd say this is your problem, BUT...
... this does tend to argue against it.

Considering all you've done, it may be worth the $150 or so to buy an aluminum/plastic radiator for it from RockAuto or Amazon, just to see whether that fixes it.


Having said that, the other thing that comes to mind with your description of fast boil-over (you didn't say whether at idle or driving) is a blown head gasket.
Have you checked compression and leak-down?

- Eric

 

What temperature is it running, just saying its hot means nothing to us. Blowing water into the overflow could simply be an overfilled radiator.

 

I'm not ready to scratch anything off the suspect list. I haven't checked compression but it's all been freshly machined and this is a brand new set of FelPro gaskets. I don't know what would have caused a quick failure in only the initial firing and break-in.

When I was holding it at 2000 or so RPM's during break-in, it didn't seem to overheat, but I was starting to get a little sizzle out of the overflow tube. The idiot light never tripped and it's a brand new sending unit and wiring harness. Now that I'm looking through pics, I see that the bulb must be burnt out.

Saturday was the first I was able to pull it out of the garage to test drive. I drove about a mile or 2 and pulled it back in the garage. By that point, it was boiling over into the tank.

I'm not going to say that it's NOT a head gasket (or worse, a cracked head). In fact, I did have a little small amount of moisture coming out of the tail pipes when it was first started the other day, but I chalked that up to normal condensation (we have high humidity).

 

I don't have a temp gauge on it. The radiator level is within the ranges stamped on the tank. It's sitting about 3" below the neck right now, cold.

 

Hook up a temporary mechanical gauge so you can see if its actually overheating or perhaps its another issue causing the water to come out the radiator.

 

Buy the kit that tests for exhaust gas in the coolant.


That will heat things up in a hurry if there is a leak.

 

Working oil pressure and temperature gauges in operation at time of first start-up after a rebuild are not optional.

- Eric

 

What about cylinder pressure. If he has flat tops with the 260h cam that cam is kind of small. I would assume his compression would be in the 10 to 1 area . Just a thought.

 

I plan on picking up a simple temp gauge from the parts store to screw into the current sending unit location. I'm also looking into getting a compression gauge to check the cylinder pressure. Was someone suggesting that the cylinder be checked to see if it will hold pressure? Like with what, compressed air? And I don't think a cylinder won't automatically bleed off pressure at a standstill.

I've never looked into a coolant tester to see if there is exhaust residue in the coolant. That's a new one that I researched a little today after learning about it.

Compression: I believe the heads are 7A's (1972)

Thanks for the help!

Bill

 

A few motor assembly pics, FYI

 

Do you have a copper core 2 or 3 row at the moment?

 

Just popped the cap. 2-row. That's probably ALL of my problem.

Also picked up a gauge, coolant pressure tester, and block tester (chemical) from Auto zone this evening.

 

I guess you wouldn't have run the engine long enough to see if you had good flow through the tubes if you were just breaking in the engine.
It could be anything at that point, you need to see good flow with the rad cap off along with all the air locks out of the system before you can determine whats going on with the cooling system.
A good 2 row copper core with good fins (none falling out or rotted) should cool your 350 no problem if everything is working properly.
I hope this helps
Eric

 

What piston to wall clearance was used with those pistons? I believe the instructions say .0025" clearance which is .0020" too tight. It could be the high cylinder pressure and the heat from inadequate clearance. The 6cc dish would have been a much better choice with that cam choice.

 

I gave all the parts to the machine shop and they've been at this for 40 years. The cam recommendation came from Comp after the pistons were ordered.

I'm not seeing any signs of the motor dying off as it gets hot and the oil is clean.

 

What is the part number for that Comp cam?

 

My bad: Sealed Power, not Speed Pro. I don't think they're hypereutectic.

 

COMP Cams K42-228-4 - COMP Cams High Energy Cam and Lifter Kits

 

This does not add up as the factory did not use flex fans. It's either an aftermarket flex fan (not good for cooling) or it's a factory fixed fan with a thermostatic clutch.

So which one is it?

 

FWIW if your heads where 7A for 72 then chances are your cc's are closer to 68-70 if not milled ??? Those pistons sit in the hole appx .025 in most std block give or take.

so if the block was not surfaced and the heads are appx at 68 cc's and you used a run of the mill flepro head gasket which is .040 your compression is in the 9.8 range . Do you have a spec sheet for the build ???

 

I misstated: It's a CLUTCH fan off of a motor equipped with factory A/C.

 

Your math/logic on the compression is reasonable. I knew the heads had larger combustion chambers, which is one of the reasons why I went with the flat tops. The head gaskets that came off were shim style. The new ones are basic FelPro metallic, but thicker than shims.

I don't have any papers on the build other than the parts that I bought and just letting the machinist to his craft. The guy is one of the most reputable and well respected in the city, and he just happens to have lived down the street from me for the last 20 plus years. This isn't our first motor together, but it is MY first Olds. He used to handle all my stuff when I raced Street Stocks way back when.

Bill

 

I think a big part of your issue, if its overheating at idle, is not enough timing. If it currently boils at idle, try 18 BTDC, vac connected to the intake manifold. That should keep it cool at idle, but don't drive it like this. Retarded timing and lean fuel mixture are the normal causes of a hot engine. This includes intake manifold leaks, which are always a possibility if you didn't glue the life out of your manifold.

If you don't have a good water pump, it may not be doing a proper job of circulating coolant.

 

I hooked up all of the vacuum hoses exactly like the factory originally did, using the thermal vacuum switch, which has four tubes connected, one of which goes to the distributor.

When I was setting the timing, I put a vacuum gauge on the signal port that the distributor was disconnected from. It was pulling only a few PSI at idle, not enough to drastically change the timing when plugged back in.

Another thing that I noticed is that the exhaust logs seemed to be getting really hot. The paint there and at the edge of the head has started to discolor from heat. The exhaust also seems to smell rich.

What would be an alternative to provide an acceptable vacuum advance?

Bill

 

Trying more timing, are you running vacuum advance? I would call him and ask what the piston to wall clearance is at. For whatever reasons, Speedpro has .0025" as the piston to wall clearance in their instructions. You need .0045" or galling and overheating can occur. No different that stuck center exhaust guides on a set of Olds heads that have been freshly machined. It has happened to a few, shops that builds a lot of motors don't know the Olds V8 needs a few thousandths extra clearance on the four exhaust guides near the crossovers. It really isn't your machinist's fault if these same wrong instructions are going out with these pistons. He probably builds Olds engines once in a blue moon. Your cam is on the small side, I would check at least one cylinder to see where you are at for cylinder pressure.

 

And I'm only pulling 15 inches of vacuum off the manifold at idle. I was expecting a lot more. I used to have to run 16" at 1000 RPM by rule on Street Stocks and was able to get that with 280 degree cams, but with a different lobe split at 110 degrees.

 

Your new configuration (compression, cam, amount of piston dish, carburetor settings, etc.) may require a different vacuum setup, and different timing curves, than the factory setup did.

I would connect the distributor vacuum advance directly to manifold vacuum and work from there, at least for now.

It would also be advisable to get a distributor re-curve kit so you can set up the vacuum and centrifugal advances closer to what your new needs are.



The paint near the exhaust ports will burn off. They all do that.

The rest of it, though, sure does sound like retarded timing. I'd say keep advancing it.

- Eric

 

On Chevy's with the old cast iron heads (before the Vortecs), we used to set them up to have a slow timing to start but then to go to 36 degrees all-out at RPM. The Vortec is a more efficient head and works better at 32 degrees, causing less negative work on the piston, making more power. I have NO CLUE what these Olds motors like as far as timing.

In any case, I know that the vacuum advance does next to nothing at idle right now. I know if I plugged it into the manifold, it should run up pretty quickly.

 

Same thing: 34-36 degrees all-in by about 3,000 RPM (maxxed RPM may vary from 2,500 to 3,500 depending on what the engine likes).

- Eric

 

Aftermarket cams like additional advance at idle. The problem your going to have is that if you run a lot of initial advance without limiting its total timing your engine will ping severely. You can't compare your engine to a Chevy Vortec setup because the ignition systems are different.

 

I wasn't comparing it to the Vortec, but was just using that as a talking point. I figured the older Olds heads were probably more akin to the old Chevy's.

Timing problems definitely have my ears perked up. I think that's the most plausible explanation so far. I'm going to play around with that tonight along with the temp gauge, pressure test and block leak test.

There is also an old ignition guru in town that all the racers use. I may ring him up.

 

You can experiment with it at idle. You can crank in as much as 30-36 degrees at idle to simulate distributor initial advance with vacuum setups to see if your temps change. Don't rev the engine.

 

STOP.

First, WHY are you using the stock TCS and associated thermal vacuum switch? This system disables vacuum advance at idle and leads to overheating. Bypass it, connect the vac advance directly to manifold vacuum.

Second, maybe I missed it, but is the car overheating at idle or at speed? Big difference in the potential causes.

Third, is it REALLY overheating, or is this your "calibrated" hand feeling the temp? Did you ever install a known good temp gauge?

Fourth, do you KNOW the vacuum advance is working? How about the mechanical advance? Look up the other lengthy thread about an overheating Cutlass this summer where the owner spent many unnecessary dollars on "fixes" when the problem ended up being a stuck advance mechanism.

Fifth, if you suspect head gasket, run a leakdown test.

Finally, STOP buying parts until you do the diagnosis.

 

Joe - Thanks for the concise points!

First off - NO MONEY has been spent on parts trying to slay this dragon. I've only picked up a gauge and testers that I BORROWED from Autozone on their tool loan program.

What's happening is that the cooling system is boiling over. It did it after being run for about 15 to 20 minutes, but even after 5 minutes in the garage I was seeing a sizzle at the overflow port.

The vacuum advance IS working, but I don't have any calibrated measurements to know to what extent. Similarly, the mechanical advance moves freely, I can only assume it's working when it's being spun as the motor is rotating.

Leakdown and fluid tests are on deck to be performed tonight when I get home.

Bill

 

Either get a timing tape or scribe the balancer at key advance points and use your timing light and tach, along with a vacuum gauge, to map the vacuum and mechanical advance curves. If you have a vacuum pump, you can apply a known vacuum to the canister and read the advance with the timing light. Plug the vac advance and do the same for the mech advance by holding RPMs at fixed points while watching the timing marks. A dial-back timing light does the same thing without needing to calibrate the balancer.

This is a good summary of how to map your advance curve.

 

Had I thought about it, I would have scribed the balancer at 10, 20, 30 & 40 degrees when I had it in my hand (it's new). I'm going to do that on the car now. My timing light isn't the dial type. It just shoots on spark.

 

If not, you can do the same thing by connecting a vacuum gauge with a T fitting and sucking on the other end of the hose.

- Eric

 

Trust me, Olds like a lot of part throttle timing but your high compression and smaller cam will limit the amount. I ran the swirl port sbc TBI tune with my 8.5 to 1 Olds 350 in my 94 4x4, I needed 10 degrees advance just for it to not back fire and stumble terribly. Actually 20 degrees base over the stock 0 setting was even better. Try manifold vacuum advance, listen for pinging. On the street 38 total feels stronger but is slower at the track. Shoot for 36 total, get a dial back light and use the highest octane around. The Crane kit with lighter advance springs and adjustable vacuum advance canister would be good to bring in more advance sooner and limit vacuum advance if necessary.