65 Corsa Turbo Overheating at sustained highway speeds

[bbiancaniello]

I am having overheating problems with my 65 Corsa. During normal "City Driving" the cylinder head temp gauge reads about 400 degrees. Once I get on the highway and maintain speeds at or above 60 mph, the temp gauge readings increase to over 500 and the alarm sounds. I have confirmed that the gauge is working properly and the engine truly is attaining those high temps. I have been advised to check for leaks in the intake system and that perhaps the engine was running too lean. I checked and replaced the seals. There are no leaks and the engine still over heats. In addition, it seems that the problem is actually getting worse as now it only takes a few minutes for the temp to increase. Does anyone have any ideas of the cause and the repair?

[joelsplace]

Retarded timing makes them run hot.

[bbodie52]

Welcome to the Corvair Forum!

I would like to encourage you to expand on your post and tell us more about yourself, as well as about your Corvair. Your personal assessment of your mechanical skills and abilities helps a lot. Members of the Corvair Forum love to be helpful in assisting other Corvair owners with technical support and advice, but it helps a lot if we have some understanding of your technical background and mechanical abilities, your Corvair-related knowledge, etc. Helping us to know more about you, your Corvair, and you plans for your Corvair will help us to write comments to you that are tailored to your needs and experience. Knowing where you live may also help, as you location may suggest some possibilities or solutions.

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Common and Useful Corvair Websites

viewtopic.php?f=225&t=6007

The average of 400 degrees is normal for your turbocharged engine and for most Corvair engines. During one hot summer, I drove from Atlanta to Los Angeles in 3 days in our 1965 Corsa coupe (140 hp engine) via a route that took us through Oklahoma, Texas, New Mexico, Arizona, and the Southern California deserts. The car was heavily loaded with two adults, two children, and a full load of luggage (we were returning from a 3-year tour of duty in Germany, and driving from the east coast to our next military assignment in California). Although the passengers were all hot, the car never acted up or overheated, and the gauge always stayed at 400 degrees or less.

Properly-tuned Corvairs have more than adequate cooling systems to dissipate normally-generated engine heat. You should check to ensure that the thermostatically-controlled air exhaust door are not jammed and that they are fully opening. Sometimes small animals invade the engine compartment and build nests under the top sheet metal shroud, clogging the cylinder head and cylinder barrel cooling fins with debris that prevents adequate cooling. You should inspect for this possibility.

Improper carburetor tuning, a carburetor defect, or a vacuum leak in the intake system can cause the fuel/air mixture to run lean, which can overheat the engine — especially when the turbocharger is providing the engine with boost pressure. Vacuum leaks can be at the carburetor mount, the large-diameter hose that connects the turbocharger outlet to the intake manifold crossover (the hose may be loose or damaged/split). The nylon tube that connects the manifold vacuum/pressure gauge to the engine can be loose or damaged. The crossover manifold tube can develop an air leak. If you remove or examine the spark plugs, they may shows signs of a lean-running engine.

The engine may be creating too much heat due to factors other than the cooling system. A proper air/fuel mixture will help your engine run cool and to its full potential. Most overheating issues related to air/fuel ratios are the result of a lean mixture, which causes the cylinders to run hotter.

Looking Beyond the Cooling System for Common Overheating Cures
https://www.speedwaymotors.com/the-tool ... ures/28793


Does your engine only overheat when operating under turbocharged boost? (As indicated by the manifold pressure gauge). There could be a possibility or a malfunctioning pressure retard device on the distributor, which is supposed to retard the timing under turbocharger boost. If it is not functioning the timing may remain too-far advanced, which can cause detonation in the cylinders and possible overheating. Also, you must only use Premium high-octane fuel with the turbocharged Corvair engine.

Do you hear any sounds of DETONATION from the engine while accelerating? This may be a pinging, or rattling sound that stops when you take your foot off of the pedal.


Corvair Overheating Questions.(Has yours ever overheated?)
http://corvaircenter.com/phorum/read.php?1,803155

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Turbocharged Corvair Engine Overheating
https://books.google.com/books?id=FPA9E ... ng&f=false

[terribleted]

have you checked the obvious things like debris on top of the oil cooler or blocking the cooling fins on top of the cylinders and heads? Are the thermostatically controlled air outlet doors at the lower rear of the engine opening?

[bbiancaniello]

Thank you for all of the advice. Here are a few pics of my 65. I have had it for about 4 years. I have had the engine rebuilt, installed a new carb and added electronic ignition. I am a clear amateur when it comes to Corvair engine operation. I have reached out to a local club, but no one is available to help with the engine work so I depend on regular mechanics to support. The engine normally runs at 400 degrees until I attempt steady higher speed driving (60mph and above). I have checked for air intake leaks and have found none. I have checked air exhaust doors and they seem to be operating properly. The turbo does kick in around 3500 rpm and does boost but the engine still runs very hot and usually alarms above 525 degrees. Because of my limited knowledge and lack of proper equipment to get into and under the engine, I take the car to a local mechanic that has done work for me before. I do have the book on the carb and I have the shop manuals as well. I am just not mechanically knowledgeable or equipped to do the work if the engine needs anything but simple repairs.

[terribleted]

There is a cover over the top of the oil cooler. It is located right under the rear of the alternator and removes with 2 screws (normally 5/16 heads). remove the little cover and peer under it at the top of the oil cooler. If there is anything in there clean it out. Any debris on top of the cooler will block air flow thru it and make the engine run hotter. It is also common for debris to get on top of the cylinders and heads. Since you have had the engine disassembled and rebuilt there should not be a lot of debris in this area, but, the top of the oil cooler is still suspect as anything that gets in thru the fan tends to land on top of the cooler. Simple to check and might be related to your temp issues.

[joelsplace]

The lean and optimal labels in the picture are reversed. Clean plug is lean.

[bbodie52]

» Fri Sep 13, 2019 7:15 pm

The lean and optimal labels in the picture are reversed. Clean plug is lean.

CORRECTED

That makes sense. Good catch!

[bbodie52]

An inaccurate timing mark on the crankshaft pulley (harmonic balancer) could cause inaccurate ignition timing to be set at the distributor. Although a remote possibility, inaccurate timing could cause an engine to overheat. You might check the harmonic balancer for slippage, as well as checking the function of te pressure retard device on the distributor. Either could result in engine overheating due to a timing error.

A harmonic balancer was specified on all 164 CI engines from 1964 through 1969 (except for the 95 hp version). The harmonic balancer was intended to prolong the life of the crankshaft by reducing the possibility of stress fractures from crankshaft harmonics in the long stroke crankshaft. If present and visible, the slip check reference mark should line up between the center hub and the outer ring, showing that there has been no slippage between the hub and the outer ring, which is held in place by a press-fit using a rubber component sandwiched between the two metal components. If the slip check reference mark is not present, the timing mark on the outer ring must be in-line with the crankshaft woodruff key. The woodruff key is a machine element used to connect a rotating pulley or harmonic balancer to the crankshaft. The key prevents relative rotation between the two parts, and ensures proper alignment with the crankshaft journal associated with the number one piston at Top Dead Center.

If you ever need to replace a defective harmonic balancer, a new harmonic balancer should be purchased because the lifespan of the three-piece harmonic balancer is limited and purchasing a used, aging harmonic balancer may not be an economical choice. This is because there is no way to predict how much life is left in the used component. The pictures below will explain the variations found in pulley design over the various Corvair model years, and shows how the pulley or harmonic balancer establishes a known reference point for crankshaft and ignition system timing.










In this picture, you can see (from left to right) the woodruff key, the distributor drive gear, the fuel pump push rod cam lobe, the main journal, and connecting rod journals 1 and 2.

http://www.corvair.com/user-cgi/catalog ... ow_page=51
http://www.corvair.com/user-cgi/catalog ... ow_page=78


Part number C13270: REPRO PRESSURE RETARD #250 65-66 TURBO

Weight: 0 lbs 6 oz
Catalog Page(s): 51,78(12),TIS
Price: $ 59.00

[66vairguy]

A great car you have. Some good suggestions posted. If we knew your location we might be able to find a "qualified" Corvair technicial. Steve Goodman of Rear Engine Specialists in Colorado had a lot of experience with Turbo Corvairs. You didn't mention if the overheating issue was happening before the engine was rebuilt!! Piston clearance in a turbo engine is critical due to the increased heat load on boost - too tight and the engine will can run hot, especially under load.

Another possible issue is the fresh air hose from the top shroud to the heater box. On a turbo engine is is on the drv. side and goes through the bulk head to the heater box. It's difficult to inspect (or replace) with the drive train in the car. With age the hose will tear and leak cooling air. Often it's not replaced unless the drivetrain is out since it's hard to get to. You can remove the hose off the engine top shroud and block the opening (temporarily) to see if this solves you overheating problem.

Good luck - nice car.

[bbiancaniello]

I checked the plugs and they look normal. Not running lean. I also checked the oil cooler fins and they are clean. I have not removed the top or bottom shroud, but did look inside top shroud when checking the plugs and did not see any debris. I am still searching for the cause of the over heating issues at sustained higher speeds.

[joelsplace]

Did you check the timing? Turbos run hot because they are turbos but also because the factory timing is severely retarded at highway cruise speeds. They have no vacuum advance to move the cruise timing up. Initial timing on the turbo engines is much more advanced than other Corvairs. My Spyder started overheating on the highway when I went from 185/80R13s to 205/60R13s because of the extra 500rpm. They are right on the edge.
Besides the timing it always helps a lot to de-flash the heads.
Clark's sells a vacuum advance/retard unit for the turbos.

[bbiancaniello]

Thanks !!
I see you are in Northlake. I live in McKinney. Maybe we could meet for coffee and discuss cars?

[bbiancaniello]

I have been running 205/60R15s for the entire time I have had the car

[joelsplace]

You should come by and check out what my wife calls the "Corvair rescue".
Mine immediately started getting hot on the highway when I switched tires. It would get hot enough that I would slow down on the 12 minute trip to Denton at 70mph.
Your tires are about the same diameter as stock so that shouldn't be the issue.

[thewolfe]

A loose fan belt that is slipping can cause overheating. Probably not your issue but one more thing to check.