The ever popular BB overheating discussion

[Michael Hampson]

I have never driven a '68 L71 tri-power, including my own, for any length of time. I've just finished the restoration. I've posted on this subject once before and scanned the archives. Here's what I've done.

1) Recored the radiator 2) New water pump 3) New fan clutch 4) New 160 deg thermostat 5) New 15 lb cap 6) Played around +/- a few degrees timing-wise.

I putzed around the neighborhood (25-35 mph, frequent stops) with weather conditions at about 90 degrees, which I guess is the most demanding on the cooling system. The temp shot up to 180 on the gauge pretty quick (thermostat closed) and then crept up from there over the next 10 minutes (cooling system couldn't handle the heat) until it just red lined and I shut it off immediately. It was hot as hell and wouldn't even run good (that's bad...) After about 5 seconds or shutting it down the overflow tube began puking for about 10 minutes.

Am I correct in saying overheating at low speeds is maybe the shroud, etc. or a bad recoring job? Or should I just expect it to overheat under these driving and weather conditions? I'd appreciate any suggestions for solving my problem.

I'm beginning to think the only solution is not to crank it up!

Has anyone had luck with putting an electric fan on the front of the radiator?

Thanks for any suggestions. I'm quite frustrated.

Michael

[Jerry Clark]

Re: The ever popular BB overheating discussion

Hi Mike:

I would be circumspect of the replacement cap, they are a known source of malfunction. Secondly it seems to me you are heating up too quickly. My 400 built quite a bit stronger than that ran 120 miles this weekend in 95 degree weather in bumper to bumper and highway and never left approximately 180 degrees, all parts replaced as you mentioned including a recore this winter. The shroud seal kit is an important part of this system and I have found the kits sold by the good DR. to be of the best quality only because they seem to have better glue and withstand the temperature longer. Don't settle for this, you have a situation that can be fixed, it's just going to require some patience and detective work.

Good Luck

jerry

[Dave W]

Re: The ever popular BB overheating discussion

Did you remove/reattach the heads during the restoration? A combustion chamber(s) may be pushing air into your cooling system. If you have a leaking head gasket on a hot Big block not even a bulldozer radiator will cool it down. Wait until the car is cold, remove the rad. cap, start the engine and let it warm up until the thermostat opens and coolant is cycling through, then look down into the tank for air bubbles and heavy foaming. Watch for losing coolant as well -Been there.

[Robert C.]

Re: Cheap Fixes

Machael, Was your engine overhauled? .030 or .060 over? Generally the engine boring will cause overheating (thinner cylinder walls) . This is a normal condition. There are many things you can try. Get a product called Water-Wetter. It mixes with water and no more than 15%antifreeze. It works for me in hot conditions. Try removing the center of your thermostat(spring etc.) and replace in the correct position. Will restrict flow , but not stop it. Solved one guys constant overheating problem. The cap is also suspect. If you can keep the coolent in, the temp can go way up and it won't hurt.Otherwise make sure it holds 15lbs! Short drives around town, and your car overheats, says that the fan clutch is slipping to much. At stop and go the only thing that cools the engine is the fan! Try getting a RPM type fan clutch instead of the thermo-type. NAPA carries them. These are all the cheap fixes I can think of. Good luck, Bob


NCRS-Texas Chapter

[Bill Lucia]

Re: The ever popular BB overheating discussion

Michael, it sounds like you have touched on quite a few of the potential problem areas. Others have also given some good places to look for problems. I would also suggest checking the carb adjustment and timing. There was an article on this in the restorer some time back but I can't recall who wrote it. Don't give up on that big blcok. Mine is a 66 and it is all original (I did have the radiator re-cored) and it runs very cool even in slow traffic. THe system was designed to work and it will. good luck

regards

Bill #8620

[Chuck G.]

Re: The ever popular BB overheating discussion

Hi Michael. I'm no BB expert, but something sounds drastically wrong. Our 69 427/400 runs at 180 degrees in all weather...just got back from Long Island...stop and go NYC traffic...no problems. Drove on the road tour to Collinsville 2 years ago...90+ degrees outside with no problems. It might hit 200 while idling in traffic on a hot day. Conventional wisdom is that a new radiator might be in your future. Perhaps the recore job is bad. Also, I'm no expert, but I am aware that different cylinder head gaskets can block different water passages in the block, causing terrific, immediate overheating. Others with more knowledge might elaborate on this. If everything...fan, clutch, water pump, etc. is new, you have to suspect the radiator, or a collapsed radiator hose...something on that order. Did you rebuild the block? Hope this helps. Chuck

[Everett Ogilvie]

Re: The ever popular BB overheating discussion

The operation of your thermostat sounds "funny" to me. You say it went up to 180 pretty fast, thermostat closed... My observation on some vehicles from cold start to warm-up has been to see the temp slowly creep up to about the thermostat value, and then to see it cool off again pretty radically the first time the thermostat opens as it releases the cool water from the radiator into the block. Sometimes you can even see when it closes again (temp comes back up) and when it opens again (temp goes down again). These oscillations are visible on some gauges and some vehicles. Anyway, the first thing I would do is drop that thermostat into a boiling pot of water to observe it.

[Michael Hampson]

Re: Cheap Fixes

Hey, everyone!

I appreciate the wide response I got! A few comments about the situation:

I intend to drive the car in less of a stop and go situation this weekend. If it doesn't overheat, perhaps that narrows the problem a bit.

Bob, yes the engine is bored .030 over, I thought that may contribute...

It's good to know I have a problem and that I shouldn't just expect it.

Thanks for your help!

Michael

[Tom B.]

Re: Air flow and gases seepage....

My first thoughts agree with Dave. Fast increase in coolant temperature like you mention can be gases leaking into the cooling system. You can check the way Dave mentioned or take it to a radiator specialist and have a fairly simple test done.

Also, check to make sure the "air flow" components of the cooling system are set up correctly. Fan 1/2 in and 1/2 out of the shroud, all foam and rubber seals in place, belts correctly tensioned (not too loose or too tight). TBarr #24014

[Rano Wells]

Re: The ever popular BB overheating discussion

I am experiencing similar problems with a freshly restored 67 L71. The engine is freshly rebuilt to factory specs and is .030 over on the bore. The radiator has been recored, new clutch fan, 160 thermosat, rebuilt water pump, and spring in lower radiator hose. The car runs great, but the temperature slowly climbs to 210 and creeps up from there. It seems to climb faster on the freeway at 65 mph than around town, but still after about 30 minutes it is running too hot on the freeway or in town to risk driving farther. Once past 210 I start to lose my idle at stop signs and it starts to kill. The head gaskets I used were Fel-Pro for that engine, someone mentioned possible head gasket problems? I don not want to add any none stock parts as I plan to show the car. What am I missing here? I have been fighting this problem since last year when I finished a ten year restoration and now am unable to show the car until I solve this problem. Help please!

[Tom B.]

Re: The ever popular BB overheating discussion

Rano,

It sounds like you've already done most of the coolant-flow checks and your 67 shouldn't have as much of a problem as the Shark cars would. Rapid increase in coolant temperature from cold to hot in a matter of minutes may be an indicator of hot gasses entering the cooling system, but it doesn't sound like that would be your problem. You may want to check for it anyway. Additionally, I'm presuming you have at least a 50/50 mixture of antifreeze-coolant and water, and you may need to check your raditator cap for proper function and pressure.

You may also want to check more on the air-flow side of problems since I haven't seen you mention many of those. You did say you have a new or rebuilt clutch fan so unless that is misfunctioning that should be alright. I presume you do have a fan shroud in place, and the check there would be for any foam or rubber seals that 1967 big blocks would have are in place, and that the correct fan position is 1/2 in and 1/2 out of the shroud. Also check for correct belt tension.

210 and slightly over doesn't sound too bad for a big block on a hot day, but if it's beginning to peg the gauge and spit overflow coolant then there definitely is something that needs to be corrected. I wouldn't recommend the use of an additional electric fan, as I've seen used or even mentioned elsewhere. That only hides correcting the real problem. TBarr #24014

[Tom B.]

Re: Add on

Rano,

Sometimes ignition timing will play into overheating problems, but not just when it's off by a little bit, usually when the timing is SEVERELY off. Also, I've seen my own idle decrease a LITTLE under excessive cooling system heat, but again engine temp was more extreme, like around 225 or 230, and my engine or idle wasn't to the point of stalling. TBarr #24014

[Duke W.]

Good point

Ignition and idle mixture should always be checked for any overheating or hot running condition, and I don't just mean the initial timing. Is the centrifugal advance operating properly? How about the vacuum advance? If you've got TCS I'd recommend disabling it. Late sixties to mid-seventies was the era of crude emission control technology. One strategy was to retard timing - and I don't just mean initial timing. Centrifugal curves got lazy, and vacuum advance was often only "on-line" in top gear. This increased EGT, which helped oxidize HC and CO in the ports and manifold, but it also threw a lot of extra heat into the cooling jacket and reduced efficiency i.e. increased fuel consumption. TCS deactivated vacuum advance in the lower gears. Also, many vacuum cans were ported to an "off-idle" vacuum source so there was no vacuum advance at idle. Recommend routing it to a full vacuum port. The engine will run cooler, idle more smoothly, and fuel consumption will be reduced. Just reset it back to production configuration if you have to get an emission test.