help with overheating 79' 308 USA

Air will be sucked into the expansion tank whether you remove the cap or not as the engine cools. That's a normal function of a radiator cap - seal against pressure; open with vacuum.

You can do as suggested - fill the expansion tank and vent it to a catch tank. That is what most cars do - they maintain a full coolant system and the catch tank receives the overflow as the coolant expands and then the engine sucks that overflow back in as the engine cools.

This was a common modification back in the days before cars came with overflow tanks/bottles for that purpose. By the time frame of 3x8's most cars had them. Ferrari obviously felt that if the coolant level in the expansion tank was correct, there was sufficient space in the tank for coolant expansion/air compression and that no catch tank was necessary.

Based on my '89 328, I'd agree; can't speak for other models.

 

Are you sure the standard 308 cap is designed to open with vacuum?

 

The little valve on the bottom of the correct 3x8 cap IS lightly spring loaded shut but a bit of vacuum will open it.

 

I have to say I think the direction the conversation is going is distracting to the OP. He really really needs to sort out why his engine is running hot and why excess air is getting into his cooling system. It's not due to the expansion tank. In all the yrs of hot rodding these engines, once properly bled, the system runs as designed. No over boiling etc.. esp with Evans as it simply can not do that, it's a literal ZERO pressure system.

Adding over flow tanks will not solve the problem, it only masks something else going on.

Please diagnose and find the reason for the overheating. It doesn't take much to warp the cylinder heads on these engines... Seen it many times. Quick check list..
Is it running proper AFR?
Pressure test the cooling system
Combustion leak detector is a quick test and inexpensive tool for checking the air in the cooling system... If it shows combustion gas... Time to replace the head gaskets.

The only goofy thing with the 308 cooling system is the dual heater cores sitting high... Otherwise the system works with little issue. I believe the 328 shifted the cores down a touch and tilted the radiator to improve air purging. But over time the system will self bleed, hence the air gap in the expansion tank.

 

Thanks Mike. Gotta check that next time I'm in the garage.

 

"It should mean there is still air pocket somewhere in the system."

Nice tool! BUT I'm not confident that "air pocket" is the only possible source of the overflow.

The amount of coolant in the bottle is not really very much - looks like a lot due to the height but the shape of the bottle means there is probably not much more than a (coffee) cup of coolant. Within the expansion tank, given it's surface area and associated volume, I'd think that's probably not much more than 2.5-3 cm of height within the tank.

I know you said you set the cold level at 6cm below the neck of the filler. Do you mean below the base of the neck, where it is attached to the tank, or below the top of the neck?

I guess what I'm saying is that if you lowered the cold coolant level to, say, 3cm below where you originally set it, there might not be any overflow at all. I think that due to the very lengthy cooling system in these cars, there's enough variation in total coolant capacity that could easily be a few cm difference in "correct" expansion tank coolant level from car to car.

Just some thoughts...

 

Another thing is that if the air is trapped in the heater core it has no effect on cooling unless it prevents the system pressure from increasing enough, when hot, to prevent cavitation and/or boiling. But this isn't a problem with Evans. So if the car is over heating and no coolant is expelled when the cap in on the tank, air in the heater isn't the cause of running hot.

 

Was the car hot (thermostat open) when you observed the rising coolant level in the "tool"?

Using the concept of your tool and if you wanted to dispel your concern for the heater cores (I agree with John's comment) if you had a large vessel filled with coolant in the filler neck, your heater cores are no longer the highest point in the system. You could open the heater valve and any air trapped in the heater cores should shift into a position where it can be released through a bleeder.

PS: is that some sort of check valve you have in the small hose from the thermostat housing to the reservoir?

 

Heater cores are not the problem, they have their own circuit which bypasses the radiator and, unlike the radiator, do not have a top to bottom flow path. Inlet and outlet are both at the top so they do not trap air as does the radiator. Furthermore the high point on the coolant manifold on top of the block is where the bleed line connects to the top of the expansion tank so the engine will self bleed. The only place where air can get trapped is the top of the radiator.

The system contains about 5 gallons (18 liters) of coolant. Pressurizing the top of the expansion tank to 1 bar doesn't tell you anything, the system runs at 1.1 bar (or 0.9 bar if you still have the original cap) so if there were a leak, you'd see it and you'd be constantly losing coolant. When you put the inverted bottle on the filler neck you were running at no pressure so what you are seeing is not how the system will behave with cap sealed and pressurized.

If you want to check the head gaskets you need to do the cylinder leak-down checks. To do that you'll need to get access to the crank pulley so you can rotate each cylinder to TDC then pressurize and listen for leaks into the coolant system. You can start by aligning the PM 1-4 mark on the flywheel then look through the oil filler cap. If you can see the timing mark on the intake cam then you are at #1 TDC, if not then you are at #4 TDC. Start with that cylinder then each 90 degrees of rotation will put the next cylinder in the firing order at TDC. The firing order is 1-5-3-7-4-8-2-6.

 

Im sorry I can’t help with this and I wish you best luck to solve your problem.

It would drive me crazy to experience something similar.

 

Agreed.

If there is trapped air in the system, when the cap is on the volume of that air would be approximately 1/2 that with the cap off. Based on your pictures it would suggest that such a reduction in air volumes would actually leave the coolant level in the expansion tank below the cap level, thus there would be additional air in the expansion tank under pressure. The fact that Evans doesn't boil when hot allows you to slowly remove the cap when hot, reducing the system pressure by venting the air in the coolant tank, then allowing any air trapped elsewhere to expand and push coolant out of the tank. With regular coolant such a reduction in pressure results in flash boiling and the explosive discharge you see when taking the cap off a hot system. The reality is that while coolant temperature at the gauge sensor point may be 180 - 195*F, internally there are areas where coolant temperatures are well above above the boiling point for normal coolant at atmospheric pressure, but apparently not above that of Evans.

That said a little research shows a couple of thing. 1) While Evans doesn't boil, it does expand, and more than the typical 50/50 mix coolant. 2) Evans coolant has poorer thermal and heat transfer properties than normal coolant. Thus I would expect that when filling with Evans you might need to slightly under fill the system to allow for the additional expansion and I would suspect that the engine would run a little hotter.

All that said, it doesn't resolve the problem that you felt the car was running hot before you made all the mods and switch to Evans. But what isn't clear to me (I haven't read all the posts carefully) is if you are just running hotter than you think you should or actually over heating to the point where 50/50 coolant boils over which would imply temperatures above 250-260*F when the system is pressurized.

 

Maybe I'm not getting a good enough view but it sure looks like the fuel return check valve is in your coolant hose.

 

Oh boy ....
Evans is a PITA coolant to setup... Seriously it's the one thing I don't like about it, however it's fantastic at what it does and keeps the big bore engines we build from melting down. Critical that the system is flushed and bone dry, including heater system.

Evans recommends in their literature a brix scale reading of 56 or higher as I recall. You don't say what the pictures of the scale are, I'm assuming one is the coolant from a bottle and the other is what's in the engine? The second refractometer reading shows water...a fair amount.. 47.5 is something like 20% water...

You mentioned it holds at a steady 195*.. if so, here's what I'd do. Remove approx 1qt of Evans from the system. Run engine.. and note where the level rises to. Is there bubbles forming in the coolant? Does it go cloudy?

I think you're dealing with excess water in the coolant. Unless you've got bubbles and exhaust gas puffing out of the expansion tank that you didn't mention.

Here's the reality, Evans will have the engine run a bit hotter then a 50/50 mix. I see on our engines a steady fluctuation from open/close of T-stat 175-195*F. The benefit of Evans isn't colder running, it's corrosion protection, stopping the galvanic process and flash boiling cavitation that occurs in the hot spots between the liners in the engine, esp on our big bore builds. (We also use an increased capacity radiator).

 

To check the head gasket as a few people mentioned you need these:

https://www.amazon.com/Block-Tester-BT-500-Combustion-Leak/dp/B06VVBSFTF

https://www.amazon.com/OTC-5609-Cylinder-Leakage-Tester/dp/B0030EVL60

 

Just an FYI - I did have a blown head gasket and I did have combustion leakage into the cooling system however I used the Block-Tester at least half a dozen times and always got negative results, the fluid never changed color. I even tested it at the tailpipe to confirm it was working and it was but it never caught a trace of combustion gas at the expansion tank. I finally confirmed my head gasket leak at #4 cylinder with the leak-down tester.

 

Even with the increased temp of Evans and we're only talking about an increase of maybe 10*F it's the better coolant due to even temperatures inside the engine, corrosion is no longer an issue.
195*F coolant temperature is perfectly fine BTW.

What is the running temp of the engine? Is it stable?

 

Minoru-san, it looks like there is a restriction in the water flow circuit. Would check if for whatever reason a rubber pipe is pinched somewhere and/or if the water pump is functional

 

Please make sure that the air flow is correct: some time the fans may be connected in the wrong way and the air is pushed forward and not in the direction of the driver