Avanti overheating

[IndyJimW]

I do not believe that there is a design problem with the Avanti that causes over-heating!

There, I’ve said it and stirred up the pot now here is why I believe this is just a myth.

My background - I have my own shop and have been an ASE Master Auto & Truck Tech for over 25 years and a professional mechanic for 33 years.

My Avanti – ’87 Coupe with a Monte Carlo chassis. Standard body, no holes in fender wells. When I first purchased it, the temperature gauge would read 205 degrees at all times, idle to interstate with or without A/C on. I hooked up my scanner and it reads 195 degrees, same as thermostat, so gauge is off a little. I installed an electric fan to eliminate a LOUD wind noise from the shroud that made the car a pain to drive, no difference in operating temperature. Installed an air dam to hide the bottom radiator cross member, no difference in operating temperature. Last summer I installed a 180 degree thermostat to see what would happen, operating temperature is now 180 degrees at all times. My engine temperature is no different then the Monte Carlo body that supplied my chassis.

Some of the problems that could cause overheating;

1. Bad radiator cap not holding pressure, this will cause coolant to boil at a lower temperature.

2. Bad or missing thermostat, will not keep engine at correct operating temperature. No thermostat may cause engine to run hotter.

3. Fan belt loose not turning fan fast enough.

4. Fan clutch bad not turning fan fast enough.

5. Water pump blades corroded not allowing coolant to flow enough.

6. Distributor advance wrong making engine run hotter.

7. Plugged radiator, this can be inside or outside.

8. Head gasket leaking.

One of the biggest problem with vehicles from the late seventies and earlier is rust in the cooling system coating the inside of the block and not allowing proper heat transfer to the coolant. I worked for a fleet for 23 years beginning in 1975 and they would lose at least one engine a month to overheating during the winter and two a month during the summer. The people in charge would not use anti-freeze year round or install overflow tank systems because of the cost. New management took over in the late eighties and I talked them into overflow systems and using anti-freeze year round and the engine losses dropped by 90%.

Back in the sixties a mechanic for C&F Trucking discovered that the air pocket that was left in the top of the radiator for expansion was causing problems with the cooling of the engine. As the coolant expanded the air would mix with the coolant and travel in the system causing hot spots and rust inside the block. He designed the over-flow system to allow the coolant to expand without allowing air into the system. All the truck and automotive manufactures started installing the system on their vehicles in the early seventies. In the late eighties I saw an interview with the inventor on TV; he said that he was suing the manufactures because they didn’t pay him to use the system. He won his lawsuit in 2000 and became a very rich man.

The system uses a double seal radiator cap that allows the coolant to travel to the overflow tank during system heat up, then when the engine cools down it causes a vacuum to suck the coolant back into the radiator instead of air.

Test the radiator cap for pressure and make sure the seals are good, also make sure that the hose to the overflow tank is good with no leaks. Mark the overflow tank level cold, the level should rise as the engine reaches operating temperature and return to its original mark after the engine cools down. If the level doesn’t move you have a leak in the system allowing air in.

Always use a 50/50 mix of anti-freeze for best protection and replace it as recommended because the additives wear out. The anti-freeze may still read OK for freeze protection but have no more additives to protect the engine. If you don’t want to install an overflow system on your older Avanti then add a product to your coolant like Pencool Coolant additive, it will keep the inside of your block looking like new.

Jim Wood

[Dennis]

Thanks for your comments. I initially had no problems with over heating in my '63 R2, but on one hot day, while waiting 45 minutes in line for a meet, it began to overheat and run roughly. Changed the distributer condenser, and ran fine - until the next prolonged idling, when it kept stalling as it got hot (220). So 2 problems: 1, the overheating is a new problem (so not a design flaw, but a symptom of something else; 2, I have checked everything you mentioned as best I can myself (I am no mechanic!) - it runs reasonably smoothly, but still over heats at prolonged idle, and cools right down on the road.

Any thoughts? Should I get an electric fan for the radiator? The engine has 10,000 miles on a complete rebuild, the fan seems tight, speeds right up with increased RPMs, belts are good, no leaks, idle speed 5-600 RPM.

Thanks

Dennis Smith

smithden1@comcast.net

[ernier]

I don't think hitting 220 at idle in hot weather is necessarily an overheating problem. I do know that ever since I blocked the exhaust crossover I don't have any problems with stalling or poor idle quality when things get warm under there. Don't be afraid to raise the idle a little either. Changing the ignition over to a Pertronix unit will keep the ignition system from reacting to higher temperatures.

As far as the fan, open the hood before you shut the car off when it's nice and hot; the fan should stop with the engine and not continue to spin. If it makes a turn or two after the engine is off you could use a new fan clutch. Also make sure the fan is on the right way.

Ernie 64 R2 R5388

Thanks for your comments. I initially had no problems with over heating in my '63 R2, but on one hot day, while waiting 45 minutes in line for a meet, it began to overheat and run roughly. Changed the distributer condenser, and ran fine - until the next prolonged idling, when it kept stalling as it got hot (220). So 2 problems: 1, the overheating is a new problem (so not a design flaw, but a symptom of something else; 2, I have checked everything you mentioned as best I can myself (I am no mechanic!) - it runs reasonably smoothly, but still over heats at prolonged idle, and cools right down on the road.

Any thoughts? Should I get an electric fan for the radiator? The engine has 10,000 miles on a complete rebuild, the fan seems tight, speeds right up with increased RPMs, belts are good, no leaks, idle speed 5-600 RPM.

Thanks

Dennis Smith

smithden1@comcast.net

Edited July 22, 2008 by ernier

[Dennis]

Ernie,

Thanks for your thoughts. I agree that 220 is not outrageous, but this car never got above 200 before that really prolonged idle - so I was concerned that something might be going on. The fan stops right away when the engine is off. I increased the idle speed as you suggested (it was actually 3-400rpms before I adjusted it this morning) to about 6-700 rpm, and it seems to like that. I am intrigued by your blocking the cross over exhaust. I do have a "silent muffler"option (quiet tonemufflers and resonators), so I assume I have a cross over as shown in the parts catalog, but I never noticed. What is it's purpose, when there apparently isn't one in the standard glass pack system? I presume I'd need to take it to a muffler shop to accomplish this. Also, what is a Pertronix system?

Again, thanks for your comments and suggestions.

Dennis 63 R2 R3821

PS I'd include a picture (it's the same color as yours) if I could figure out how!

[ernier]

Actually, the crossover is a passage below the carburetor inside the intake manifold. The heat riser directs exhaust through the inkake to warm the air so the mixture atomizes better in when its cold out. Check the operation of the heat riser, right side exhaust manifold between the manifold and headpipe, you should see the valve move when you rev the engine. If it doesn't then too much heat is being directed into the intake manifold and boiling the fuel in the carb.

Blocking the crossovers stops the exhuast from entering the intake and keeps the carb a lot cooler. Before I did it the car would stall, stumble and belch black smoke when I would pull away from a light in warm, not even hot temps. What happens is fuel is evaporating from the bowls of the carb and vapors are being pulled into the engine with the outside air creating an overly rich mixture.

Blocking them requires removing the intake manifold and installing gaskets that do not have an opening for the exhuast to enter the intake. I welded metal into my intake and used the special gaskets but that might be overkill. I have run my car in some very cold temps ( I don't even have a choke plate in my carb ) and really never had an issue. I think the supercharger warms the air enough to allow cold weather driving without a crossover.

BTW, changing the intake gaskets is easy. The only precaution is to make sure you don't over-tighten the bolts. The hold down clamps can be weak and then they start to split and not do their job. In fact if you went that route I would get gaskets and clamps and replace both.

The Pertronix unit is a replacement for the points and condensor. Very reliable and simple to install. I noticed right away that my car started more easily and idles smoother after installing the Pertronix unit. I mention it because it is not effected by heat and never needs any adjustment.

One simple thing I would mention is the ratio of coolant to water. Water cools better than anti freeze and if you have a mixture that is more than 50-50 the wrong way you might be losing a little efficiency.

Ernie

Ernie,

Thanks for your thoughts. I agree that 220 is not outrageous, but this car never got above 200 before that really prolonged idle - so I was concerned that something might be going on. The fan stops right away when the engine is off. I increased the idle speed as you suggested (it was actually 3-400rpms before I adjusted it this morning) to about 6-700 rpm, and it seems to like that. I am intrigued by your blocking the cross over exhaust. I do have a "silent muffler"option (quiet tonemufflers and resonators), so I assume I have a cross over as shown in the parts catalog, but I never noticed. What is it's purpose, when there apparently isn't one in the standard glass pack system? I presume I'd need to take it to a muffler shop to accomplish this. Also, what is a Pertronix system?

Again, thanks for your comments and suggestions.

Dennis 63 R2 R3821

PS I'd include a picture (it's the same color as yours) if I could figure out how!

[IndyJimW]

Great info Ernie! Ahh, the memories of working on carburetors and points. I installed many a one-way vacuum check valve to stop Chevrolet exhaust cross-over valves from rattling during take-offs.

With all the different engines used in the Avanti I’m kind of interested in what is a normal running temperature, I remember that the 400ci Chevys were a bear to keep from overheating no matter what vehicle they were in.

If you have an engine with a 10psi radiator cap, the cap would raise the boiling point of the coolant about 2.5 degrees for every psi, from 212 degrees to 237 degrees. So the engine doesn’t overheat by design until the radiator cap vents coolant at 237 degrees. But most of us feel that an engine is RUNNING HOT at over 210 degrees. I believe that today’s engines last longer because of heat, newer fluids, EFI and electronic ignition. The problem that you run into with older cars is that the fuel and ignition systems just can’t handle the heat. I’ve never heard of a newer car with “vapor lock” that disappeared with EFI and its higher fuel pressures. Some of the newer coil-on-plug ignition systems can produce 80,000 volts and with electronics heat just doesn’t break down the system.

Dennis it sounds like the idle was a little too slow and your fuel system and ignition didn’t like the added heat it caused, Ernie has some great ideas to help you with those. I believe that most Avanti’s that run hot have a simple problem with the cooling system, BUT experience has showed me some mind numbing problems also, in those cases it takes time and the willingness to look at each piece of the system at its basic to find the problem.

I finally found the problem with my wife’s Jeep running hot, (Man I hate working on my own stuff) after beating me up on this one I pulled the water pump and found that the blades were loose on the shaft. Most of the time the water pump would work OK but on occasion the blades would slip and the engine would run hot, a new water pump seems to have cured it so far. (Did I mention that I hate working on my own stuff?).

Good luck

Jim Wood