Overheating

[Rob Ryan]

So here we are stuck by the side of quite a busy suburban road with the temp way over the limit.. And along come two dirt track bikers. They stop. I stare.

"Hi Dad!"Says one,pulling off his helmet. "Why are you here?"

I don't know who is more put out. Me, because junior is not supposed to have his unlicensed bike on a main road or him,:shocked: to find me here. Busted.

"Car's overheating."I say.

"Oh."He says and rides off. So much for helpful family.

But there are compensations to being stuck with an overheating GT 40. You get a lot of attention.

 

[Terry Oxandale]

Yep, it would have gotten mine. Great looking example.

 

[Rob Ryan]

Does anyone know if air in the system can cause overheating? Sounds like a very stupid question. I know air can cause an airlock, which from my Renault Gordini days, meant the water didn't circulate through the radiator at all, but on my 40 the water does circulate and still it runs too close to boiling for comfort. And this was not always the case- the cooling system hasn't been changed. Any ideas?

 

[Jac Mac]

Yes it can/does and going by this pic you posted of your car you should drill/tap the two rear corners of your intake manifold ( arrows & lines drawn in on pic) for small -3 vent/bleed lines to free any air pockets caught at the rear of the cyl heads. Due to your higher/nose down engine mounting due to the transaxle being used air gets caught at this point.
The bleed lines are just that, keep them small to only bleed air/not pass large amounts of coolant. Also have a check of your cooling system for any possible leaks especially on the suction side of the pump. The two lines at the forward end should go into either the top of thermostat housing or in your case header tank just below the cap. That header tank should also be mounted higher to function correctly.
Sounds like tricky job, but if you grab a spare intake manifold gasket to check where the intake manifold needs to be drilled/tapped to intersect the water opening in the heads its pretty basic stuff. If it was mine I would look into another header tank & mount higher & on the firewall.
You could of course have an engine issue that is causing the engine to run hotter and create air bubbles- head gaskets- ignition timing- water pump speed-low octane fuel etc etc.

 

[Rob Ryan]

Although my engine/suspension configuration has changed drastically from the pic you attached, you are telling me, I think, that air trapped in parts of the system( eg. cyl. heads) can cause overheating even if the basic header tank to radiator and return system does circulate.

Many thanks for your advice jac mac.

 

[John]

It seems to me that if you placed the reservoir tank and the filler tube above the height of the engine, all the air would automatically be purged from the rear of the manifold. That way you wouldn't have to do any drilling!

John

:chug:

 

[Bill Musarra]

If you develop vapor lock, nothing is going anywhere. Make sure you have all the loops and bends purged of air if any hoses are used. Remove the burp line from the radiator and use a funnel to fill the radiator. Routing this line back to the fill tank can develop trapped air, and until the radiator is full it may not force the air out. May have to lift the front end of the car while filling. Leave the burp line disconnected if you use this technique. Use the radiator to fill once the fill tank is full. A little tedious but it will work.

Bill

 

[Mark R]

I would think an infared thermometer might help isolate areas where air pockets exist.

Coolant could still pass through an area where an air pocket is taking up x% of the space. You would just have that area of the cooling passage that would be hotter and not transferring the heat to the cooling system.

 

[Jac Mac]

It seems to me that if you placed the reservoir tank and the filler tube above the height of the engine, all the air would automatically be purged from the rear of the manifold. That way you wouldn't have to do any drilling!

John

:chug:

Look a little closer at the picture of his header tank. He states in the post above yours that his cooling system has not been changed, and that [** if the basic header tank to radiator and return system appears to circulate **] he is running the entire flow of coolant thru the header tank, but with only one pipe???
In the pic the only connection between engine and header tank is the large fitting at bottom of tank[wide green dashed line]. Narrow green dashed line is from header tank cap to plastic overflow tank. The large fitting goes down before it connects to the water pump or wherever he has it attached [ possibly radiator return tube ] so its extremely unlikely for any air trapped in the cooling system to get to that low point in order to be pushed into the header tank and purged, and I do not see any other lines fitted from say the t/stat housing that might act as a bleed line- hence the suggestion for the vent lines.
Also the car has an Audi or similar trans that places the crankshaft above axle shaft and usually ends up with the engine being mounted in a slightly nose down attitude which in turn tends to trap air in that rear corner of each cylinder head, again the fitting of vent lines helps with this.

 

[Howard Jones]

Jac is completely correct. I have EXACTLY the same system in my GT40 and there is NEVER a problem with air in the system, It will always self purge.

Here is a diagram that has been around for a very long time. Do it like this with the addition of the rear of the intake manifold lines and all your air in the coolant system problems will be forever gone.

Here is also picture of somebody's intake manifold steam port system in a GT40.

 

[Rob Ryan]

Sorry Jac I did say my system HAS changed drastically since the pic. And the header tank, now on the firewall, has both an inlet and outlet of course. The system worked well for a year or two since these changes before it started running hot (possibly after working on it and letting in air).

My question-which you kindly answered- was if air trapped in the system (the example you gave was a cylinder head) could cause overheating even if the water circulated through the radiator and back to the header tank i.e. there was no obvious airlock.

 

[Chris Kouba]

When I was going through my initial cooling system fill, some of the feedback was to fill it with the front elevated so to have trapped air be motivated to go forward.

I used the exact diagram Howard posted and kept the header tank as high as possible. I also have a bleed line from the top of the rad to the header tank as well. Never overheated.

Chris

 

[Rob Ryan]

Have heard that before Chris, but I assume the header tank on the rear bulkhead is your highest point in the cooling system. I too have a bleed valve on the top of the radiator. But I suspect that I had air trapped, maybe in the heads, as Jac suggests, that moved to the header tank-after some months of causing the engine to run hot. I say this because I suddenly lost about a liter of water without any apparent cause and the operating temp is ( touch wood) back to normal.

 

[Grady]

Here is another problem that will make you pull over, although rare, happen to me last summer. Overheat problem caused by the impeller not turning on the water pump shaft as it rotated. This was discovered during investigation to find source of problem on a FE engine. The pump was replaced with a new aluminum FE pump and the old pump was returned to Edelbrock for their analysis. They sent me a new one back. Great company to work with. Anyone else ever had a similar problem?

I want to add I'm using Evans waterless coolant in a new rebuilt TR6 engine. So far great stuff. It boils at 375 degrees. Anyone else try this stuff?

 

[Terry Oxandale]

To add a tiny bit to this discussion; I inserted a Presta valve into a very small reservoir (a 1" diameter tube, about 2" long, which is connected through a small diameter hose to the highest point of the coolant system. Air passing this point accumulates in the reservoir after any re-fill from maintenance. Even with my "AirLift" system (which is fantastic), I still have a small amount of air in the system (but not enough to cause any heating issues) that can be bled off using the Presta valve while the engine is still under heated pressure. That equalizes the pressure so that once the engine starts cooling down, it immediately starts drawing air-free coolant from the overflow tank. I'll do this 2 to 3 cycles (it's on top and easy to get to), and end up with no more air, which means the electric pump quiets down a bit as well.

 

[Cliff Beer]

Just one minor thought on this one..... I've fitted "bleed nipples" in a couple different spots (high spots) rather than an open bleed line back to the header tank (or elsewhere). Right or wrong, my reasoning on this has been that I'd like to avoid potentially having coolant flow go through the bleed line on a continual basis, perhaps lessening the flow through the radiator.

The bleed nipple is just a threaded fitting with an internal screw and a port. Basically, you just periodically "burp" the system. I'm no expert on cooling systems but this seems to work pretty well.

 

[Howard Jones]

Grady, I'm on my third Edelbrock RPM performer. I finally gave up and welded the impeller onto the end of the shaft. You can't replace the seal after that but I've never had one last long enough to wear out a seal. I had them tell me that I could buy another one directly from them if I liked. I wasn't happy with their pumps and if I need another one I will do a Stewart

By the way there is a complete thread on this subject somewhere. The best water pumps available IMHO are Stewart pumps. I talked for a hour or so with one of there tech guys and to make a long story short its the high revs on track that kill them. Steward uses a keyed shaft.

Hint: figure out your pump speed and do not exceed 3000RPMs with the impeller. The shock load from cavitation above 3200 or so is what defeats the shaft impeller press fit. This means you need to turn the pump at half the engine speed if you track it a lot and run the engine above 6K RPMS a lot. Good luck finding the pulleys the right size. Target would be 3.5 inch diameter crank and 7 inch for pump. I have a 4 and 7 on mine and I made the 7.

Hint#2 If you try this on the street and drive slow a lot in traffic then be prepared to deal with low engine/pump revs and high water temps. Basically duel use cars will not cool well at one or the other use. Track or street.

Hint#3 electric water pumps. Constantly controlled speed unrelated to engine speed. Way to go IMHO.

 

[Jac Mac]

Seems to be a bit of misunderstanding on cooling systems here.
1. cooling systems need an expansion area- remember the old straight up n down core radiators with no catch/recovery cap or tank- you only filled them to about half way up the top tank, if you filled them above that they just puked coolant out the overflow until they found their own level- some worry wart owners never ever got used to that or learnt the principal and spent their entire automotive lives topping up the radiator. If you get the chance to have a look at the first x-flow radiators of the mid 1970's you will see the cold fill level embossed on the tank just down from the cap.

2. That all changed with the introduction of the double seal recovery type caps and with these the radiator should remain full to the top and the system is actually meant to push a little coolant into the catch tank when hot and then pull it back in when the system is cooling down.

3. While Cliffs 'burp' valves are fine perhaps on a normal road car, on a car like the GT40 or most rear/mid mount engine cars with the main coolant tubes running down/fwd/up to radiator & return the possibility for air to become trapped in the system is high, therefore permanent bleed lines to the header tank on firewall in order to keep air out of the main coolant lines are a much safer option. Again these 'bleed' lines don't need to be large, a fitting in the rear corners of the intake manifold with an 1/8" bore will be more than adequate.