1967 Smallblock Hi Temp

[Roy A.]

I have a 1967 327ci 350hp.When I run highway speed temp gauge rises coming off highway temp drops.The engine has been rebuilt 700 miles on rebuild.Engine flushed,Thermostat changed ,Rebuilt water pump & fan clutch.Timing could have this effect?Anyone have had this type of problem? Any info GREATLY APPRECIATED, Thanks.

[Mike M.]

Re: 1967 Smallblock Hi Temp

first thing to check is the temp sending unit. ac delco stamped in originals that almost always send correct message to temp guage. generic temp senders notorous for sending falsly elevated temps to cockpit. next check timing. previous posts discuss this item. good luck, mike

[Duke W.]

Re: 1967 Smallblock Hi Temp

High highway temperature is usually an indication of insufficient radiator capacity. Describe your radiator and its history. Is is the orginal "316" aluminum type or some kind of non-OE type replacement. If the former, what is the date code.

Idle overheating is often caused by a malfunctioning or incorrect vacuum advance. In any event, comparing the entire ignition advance map to OE spec is always a good idea.

Duke

[Roy A.]

Re: 1967 Smallblock Hi Temp

Duke:Yes it is a original 316 nov 66.I was trying to avoid taking out the radiator but yes a replacement may be in the future.I will check the timing hopefully thats the problem. Thanks for your response.

[Roy A.]

Re: 1967 Smallblock Hi Temp

Mike:I have changed to a lectric limited temp sender.I have tried a AC DELCO.I will check timing.THANKS VERY MUCH

[Duke W.]

Re: 1967 Smallblock Hi Temp

An original nearly 40 year old radiator is definitely suspect. Over the years deposits from the inorganic chemicals in the green antifreeze precipitate out on the tube walls and greatly reduce the radiator's heat tranfer capacity, and most cars have had indifferent cooling system maintenance in terms of coolant changes. which will cause more rapid deposit buildup and/or corrosion. Figure if you buy a new DeWitts, use a modern HOAT antifreeze, and change is every two to three years the next radiator will probably last 50 years.

Also, whenever you install a new radiator, use new rubber mounting grommets (two on the bottom and a different one on the top). It's very important to keep the radiator electrically isolated from the chassis, and this can easily be verified with an ohmmeter.

As far as the ignition map is concerned you need to do more than just "check timing". You should verify the performance of the vacuum and centrifugal advance curves with the specifications contained in the shop manual and/or AMA specs.

Duke

[Roy B.]

Re: 1967 Smallblock Hi Temp

If you have one of those guns (temp) compare temp.

[Mike McKown]

I would like to make a short response

In 1971, I bought a 250 hp '65 coupe. It was all original. I found nothing that had been replaced. It ran 180 going down the highway and in town.

In 1980, with no changes, it ran warmer, maybe 200 on the road.

It wasn't driven again until 2002. Now the temp on the road was 200+. The radiator was also starting to seep. So, I replaced it with a copper radiator which I bought used for $100. It was only a year old. Temp ran 200 on the road. Okay, but not back to where it should be with a new radiator. All this time, everything stayed constant. Timing, carburetor, thermostat, hoses, fan, clutch, belts, distributor, air cleaner, oil, filter, everything.

There is no doubt in my mind that if I went with a new Dewitt NOS design radiator, I would be back where I started 33 years ago at 180 on the road with NO changes to the engine.

I see plenty of testimonial on this and other Corvette forums that the proper original design radiator will fix overheating problems. I have seen NO testimony that a copper replacement will do the same.

Your course of action seems cut/dried to me. Maybe I'm wrong?

[Clem Z.]

from playing with race cars

i can tell you that no reconditionerd rad will cool like a brand new one,been there tried that. they always run hotter,10 to 30 degrees. i stll believe that it is because the finning does not make as good a thermal contact with the tubing as the rad gets older and this is something that the rebuilder can not fix.

[Jim T.]

Re: I would like to make a short response

I replaced the aluminum radiator in my 68 L79 with a copper radiator in 1974. I still have no overheating or high heat problems and it certainly has lasted longer than the original aluminum radiator. I am only saying that I have had some very good service with no complaints of using the copper radiator. My 70 has its original copper radiator with factory air and it keeps the temp at normal operating temperature.

[Verle R.]

Re: 1967 Smallblock Hi Temp

Roy,

I had the same symptoms you describe and tried all the options with little change. As Duke suggested, I finally broke down and bought a new DeWitts reproduction radiator. It now runs "on the thermostat" at any highway speed and street speed. Heat soak during a short stop drops back to the thermostat temp within two miles.

I'm a beliver.

Verle

[Roy A.]

Re: 1967 Smallblock Hi Temp

Verle:Thanks for your response .Yes it seems the radiator could definetly be a problem.I was hoping to keep the original radiator but these new radiators would have a definetly help. Thanks

[Gary S.]

Re: 1967 Smallblock Hi Temp

Same story as Verle's car and yours. 66 L79 ran great in town but the temp would climb steadily on the highway. Tried EVERYTHING - timing, tune-up, cooler thermostat, no thermostat, etc, etc.

I finally broke down and bought a DeWitts repro aluminum which I should have done years before. I could finally drive anywhere and anytime at any speed.
Gary

[Dennis B.]

Re: 1967 Smallblock Hi Temp

I had the same results as Gary and Verle. I spent a long time chasing thiw high temp problem around. Put in a DeWitt direct replacement aluminum in my 66 Coupe. End of the story.