Overheating on my 65

[Chris H.]

Re: Overheating on my 65

Will do Ed. Thanks for all the ideas. I've really been stumped over this entire issue.

[Edward S.]

Re: Overheating on my 65

Chris,
When I bought my 65 L-78 in 2001 the radiator always ran at 200 and in time started to show small leaks up apound the neck. At that time DeWitt started to advertise the fact that they were now making a correct radiator for a L-78 - I bought one and must say it's been great from day 1, loses no points when being judged and runs 20 degress cooler on average. Needless to say I am really pleased with the way it performs.

[Craig F.]

Re: Overheating on my 65

Chris,
I did the exact same thing with my 65 small block and my problem was solved when I went back to the standard flow water pump. It seems that the high flow small block pump moved to much water through the system and did not leave it in the radiator long enough to cool it. I found the best cooling after installing all factory original parts, ie fan clutch, sending unit and cast iron standard water pump. It is now my belief that I would need to change to a larger radiator if I want to use the high flow pump. By the way, I was not smart enough to figure this out myself. A local guy who has been in the radiator business for 40 years gave me the tip.
Craig

[Craig F.]

Re: Overheating on my 65

Chris,
I did the exact same thing with my 65 small block and my problem was solved when I went back to the standard flow water pump. It seems that the high flow small block pump moved to much water through the system and did not leave it in the radiator long enough to cool it. I found the best cooling after installing all factory original parts, ie fan clutch, sending unit and cast iron standard water pump. It is now my belief that I would need to change to a larger radiator if I want to use the high flow pump. By the way, I was not smart enough to figure this out myself. A local guy who has been in the radiator business for 40 years gave me the tip.
Craig[/quote]

[Joe L.]

Re: Overheating on my 65

Thanks guys. Maybe i missunderstood the guy at the shop, but he did indicate that he was able to repair the unit that was in the car and if it were aluminum, he could not. I think you and Ed may be onto something here as I've tried just about everything I can think of. Do you think an aluminum unit would run cooler?

Chris-----

If your radiator is a copper/brass replacement for the original aluminum radiator, it WILL NOT cool as well as the aluminum. It will provide about 20-30% less cooling than the aluminum. However, that, by itself, should not cause gross over-heating as you are, apparently, experiencing.

The "high flow" waterpump could be another problem. On many previous occasions I have recommended against these for exactly the reason that another poster mentioned-----they move coolant too fast through the radiator and there is not enough time for the heat to be dissipated. If the pump were designed for reverse flow (i.e. serpentine belt system) as was also mentioned by another responder, that would present a MAJOR problem. You've got to determine what you've got. In any event, I would replace with a standard-type waterpump. You can use aluminum if you wish, but not a high flow and certainly of the correct rotational configuration.

[Joe L.]

Re: Overheating on my 65

Chris, maybe one more item, when the high flow water pump was installed, did you change any pulleys,alter anything else that may slow down the water pump pulley, I believe that 65 is a year that always has alot of questions on correct pulleys, What do you think Joe L ?

Edward-----


Yes, that's a possibility, too. However, unless the mis-match was severe, I would not expect it to cause gross over-heating as, apparently, is the case here. Combined with other problems it might, though. If we knew the RPO of the engine and the OD of the pullies (crank and waterpump) installed, we might be better able to assess whether, or not, this is a problem.

[Paul H.]

Re: Overheating on my 65

Put a new Dewitt's aluminum radiator in and be done with it. That is what I did with my 65 and it never runs over 180 no matter what the temp or traffic conditions are. Incidentally, I am still running the high flow water pump I tried as a "solution" before buying the radiator and it doesn't seem to have any adverse effect on it now that I have a good aluminum radiator.

[Chris H.]

Re: Overheating on my 65

Chris-----

If your radiator is a copper/brass replacement for the original aluminum radiator, it WILL NOT cool as well as the aluminum. It will provide about 20-30% less cooling than the aluminum. However, that, by itself, should not cause gross over-heating as you are, apparently, experiencing.

The "high flow" waterpump could be another problem. On many previous occasions I have recommended against these for exactly the reason that another poster mentioned-----they move coolant too fast through the radiator and there is not enough time for the heat to be dissipated. If the pump were designed for reverse flow (i.e. serpentine belt system) as was also mentioned by another responder, that would present a MAJOR problem. You've got to determine what you've got. In any event, I would replace with a standard-type waterpump. You can use aluminum if you wish, but not a high flow and certainly of the correct rotational configuration.

Great advice Joe. I'm going to check the pump to ensure correct roation as well as go back to a standard, correct rotation unit.

[Chris H.]

Re: Overheating on my 65

Thanks Craig. It's somewhat of a relief to know I'm not alone with this problem and others have been able to solve it.

[Chris H.]

Re: Overheating on my 65

Thanks Paul. In the end, after I double check the rotation of the pump, possibly go back to a standard pump, check the pullys, follow-up on all the advice from the inputs above, I will in all probability end up purchasing the aluminum radiator. I've been encouraged to get so many responses on the page and appreciate everyone's input.

[Jack H.]

Re: Overheating on my 65

It was VERY common for prior owners to replace their worn out or 'roadkill' factory original Harrison aluminum radiators with aftermarket copper/brass units... The biggest supplier is Modine.

These 'would' work, but you lost almost all of the factory design safety margin in terms of thermal transfer capacitity. Then, as these copper/brass radiators aged and lost their cooling capacity due to corrosion, the 'hot Corvette' syndrome began...

Other areas where problems can occur include: (1) fan clutch, (2) loose/wrong impeller on the water pump, (3) cooling system failing to hold pressure at rad cap & hose clamps, (4) excess corrosion and/or blockages in the engine cooling passageways, Etc.

Being from Denver, there are several classic Corvette shops with 20+ years of experience of working on these cars (Corvettes Only, Corvette City, Corvelle Automotive) who can help you IF you can't diagnose and cure the problem(s) yourself.

Note I used the term 'problem(s)'.... That's because it's often true that you have more than ONE issue working against you!

[Chris H.]

Re: Overheating on my 65

It was VERY common for prior owners to replace their worn out or 'roadkill' factory original Harrison aluminum radiators with aftermarket copper/brass units... The biggest supplier is Modine.

These 'would' work, but you lost almost all of the factory design safety margin in terms of thermal transfer capacitity. Then, as these copper/brass radiators aged and lost their cooling capacity due to corrosion, the 'hot Corvette' syndrome began...

Other areas where problems can occur include: (1) fan clutch, (2) loose/wrong impeller on the water pump, (3) cooling system failing to hold pressure at rad cap & hose clamps, (4) excess corrosion and/or blockages in the engine cooling passageways, Etc.

Being from Denver, there are several classic Corvette shops with 20+ years of experience of working on these cars (Corvettes Only, Corvette City, Corvelle Automotive) who can help you IF you can't diagnose and cure the problem(s) yourself.

Note I used the term 'problem(s)'.... That's because it's often true that you have more than ONE issue working against you!

Thanks for the help here Jack. I really appreciate the history as I think it helps expain why the problem keeps coming or pointing back to the radiator and the flow rate, thus the system's cooling capacity.

[Jack H.]

Re: Overheating on my 65

Fire up your web browser and visit DeWitts' web site. He gives an EXCELLENT technical tutorial on aluminum vs. copper/brass construction.

Most think aluminum was used because it's superior to copper/brass in terms of heat transfer. That's untrue. Aluminum is inferior.

Thermal conductivity and electrical conductivity generally covary directly. Everyone knows aluminum wiring is inferior to copper for household use!

The 'trick' is aluminum is stronger and can be 'scaled' down much futher than copper/brass (thinner tube walls that won't burst under pressure, greater cooling fin density). So, given a fixed packing density constraint (size of the radiator), it's possible to get more cooling capacity out of aluminum vs. copper/brass.

But, there's a cost/price tradeoff and weight consideration in the economic equation too!

[Duke W.]

Re: Overheating on my 65

My 65 is overheating. I've had the radiator professionally restored, installed a new hi-flow water pump, diluted the anit-freese, added water wetter, had the entire engine professionally rebuilt ($6,500), tried numerous fans (I'm back to the original 7 bladed fax and HD clutch) and I keep overheating. I've run out of ideas. Any help will be appreciated

Twenty-eight posts and we still don't know what engine you have, but a lot of things have apparently been modified.

This is what happens when various people - owners, "mechanics", and "engine builders" start diddling with GM's excellent engineering.

Your best hope is to return everything to OE configuration and OE replacement parts to get a baseline and go from their, but new correct OE replacement parts in the cooling system should solve the problem depending on how bad the engine has been cobbled up.

Just because you pay big bucks to have an engine "professionally rebuilt" is no guarantee that is was done correctly. Based on many stories here, most of the time they screw it up.

Duke