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The system pressurises naturally due to thermal expansion of the coolant into the reservoir. The reservoir has a nominal capacity of two litres, the cold fill point sits a approximately 1 litre level leaving an airspace of 1 litre above the fill point when cold. The system has about 14 litres of coolant and when it heats up from 20C to 80C the increase in volume is approximately 0.5 litres. The cold pressure is 15 psia, the free volume halves as the system heats and as per Boyle's law the pressure increases to 30 psia or 15 psig there or thereabouts. The increase in pressure has the advantage of supressing the boiling point to give a margin of comfort in terms of potential boil up and so to does the eutectic mix of glycol and water such that with a 50/50 glycol water mix the boiling point increases to something around 125C at 15 psig.
If the system is overfilled the increase of volume will cause the pressure to go beyond the set point of the cap and the result will be an overflow as the cap lifts off. However that should only release a small volume of coolant until such time as the cap reseats at about 13 psig.
If you are getting a continuous pressurisation once the motor is warm then a failed head gasket is the only contingency I can think of that can cause such. Sadly that might explain the trail of coolant left in your wake as it were. A 15 psig pressure test may not find a failed head gasket leak path directly but if it does then you know it is game set and match in that regard. Needless to say if one side has failed it is a fair bet the other will not be far behind.
When the system is working efficiently the coolant emanating from the water bridge should be at about 98C and even with the cap off should not boil but things are a bit more complicated than that as in reality there may be a degree of film boiling taking place. Film boiling is where there is a localised boiling event at the heat transfer surface due to a localised temperature gradient and the small amount of liquid droplets that boil up to form steam immediately collapse back into the liquid phase. Have you ever wondered why when boiling a kettle of water it makes a lot of noise before it boils proper? That is film boiling and the noise you hear is when the bubbles of steam collapse back into the liquid phase at sonic velocity. Most of the sound energy is damped out of course but nonetheless it is still something of a racket. The higher the boiling point the more this potential issue is supressed. You do not hear this phenomena in our engines probably because of the rest of the racket that is going on that or the design helps prevent such in the first place.
Trust the above informative and helpful- just hope it is not a failed gasket but I suspect there is a good chance it will be. The reasoning behind head gasket failure and cylinder head corrosion I have covered elsewhere. If you do eventually decide to remove the heads then do take plenty of photos of the gaskets [both sides] and the heads. However still more work to do before you resort to such. That being said if your head gaskets are still the original build items there is a lot to be said for pre-emptively removing them and checking for potential corrosion damage and nothing to be lost even if it proves to be that there is not head or gasket issue to start with.
Hopefully you will get some more suggestions as to what you can do at this stage before pulling thing apart- trust I have not missed anything obvious..
Had this problem on a Saab 9000 many years ago.
After fitting a pressure tester, I found no apparent leaks.
Then, with the tester installed but not pressurized, I started the engine and saw immediate pressure increase on the tester.
Bad head gasket.
Update: I drained the fluids and removed the plugs.
All this black muck came of the sump plug.
The oil itself looks brown and thin. A bit difficult to see in the black drain plan. I'll skim some of for a better look.
The plugs all look the same. The electrodes are gray, with the bodies black.
Looks OK to me, but would welcome opinions.
The coolant looks clean, but then I have topped it up twice while chasing leaks. Still, there is no oil in it at all.
My feeling at this point is that I am going to strip the motor and replace the head gaskets, water pump and timing belt. I don't think it can hurt.
My next question is" How do I clean the residue muck out of the engine without stripping the bottom end?
Anyway, this is what my engine bay looks like after I redid the intake and valve covers less than 500 km ago Now to take it all apart again.
Plug No7 looks a bit brighter than the rest but maybe that is due to lighting.
That the leak path appears to be the overflow pipe from the expansion tank is one thing but I would still do a 15 psig pressure test to ensure the leak path is not a sealing seat in poor condition. The seat where the cap seal sits should be clean/bright. If the test holds then with the test rig still on board run the motor until it warms up and see what pressure it rises to starting from a correct coolant level when cold.
At the moment the notion that you have a head gasket leak is inferential and ideally you want to progress to "confirmed" status if possible.
FYI I just did plugs on my car....plug condition were identical to yours....gray with darker bodies. Personally it sure doesn't look to me like you have coolant invading the combustion chamber(s).
You said you did a new radiator cap...just curious if you got the one from one of the big 3 or?
I am struggling / have struggled with the sensor on top; I swapped out the cooling reservoir with 928 Motorsports' aluminum one so had to swap...been a little gun shy about tightening it more...am doing it as incrementally as possible....don't want to break the plastic.
Can you observe the leak in action...is it on passenger side...
Head gaskets, timing belt, water pump !! bit drastic. I agree with Fred: be sure of the problem before embarking on this big work programme.
-- incidentally: I have 2 breather pipes connected to the left hand cam cover , on your picture you seem to have just the forward one.
Peter
Do you have a boroscope where you can look through the plug holes to see if there is any coolant on the pistons. Those plugs don't look like they're being steam cleaned by coolant.
When I blew my head gasket, they looked clean. Should be pics in my "Blown / Damaged Head Gasket" thread.
[QUOTE=FredR;17609588]Plug No7 looks a bit brighter than the rest but maybe that is due to lighting.
That the leak path appears to be the overflow pipe from the expansion tank is one thing but I would still do a 15 psig pressure test to ensure the leak path is not a sealing seat in poor condition. The seat where the cap seal sits should be clean/bright. If the test holds then with the test rig still on board run the motor until it warms up and see what pressure it rises to starting from a correct coolant level when cold.
At the moment the notion that you have a head gasket leak is inferential and ideally you want to progress to "confirmed" status if possible.[/QUOTE
I agree that a 100 % confirmation would be nice, but I think for my piece of mind I am going to jump in and do everything.
There has been a lot of posts lately about failed gaskets and cracked cylinders, both here and in the Aussie forums. That, together with the fact that my belt and pump is due shortly in any case make me think to just do it.
This way, I know it's done, and I don't have to do it early next year.
This, and replacing the hoses as well should fix the issue, whatever it is.
Do you have a boroscope where you can look through the plug holes to see if there is any coolant on the pistons. Those plugs don't look like they're being steam cleaned by coolant.
When I blew my head gasket, they looked clean. Should be pics in my "Blown / Damaged Head Gasket" thread.
Head gaskets, timing belt, water pump !! bit drastic. I agree with Fred: be sure of the problem before embarking on this big work programme.
-- incidentally: I have 2 breather pipes connected to the left hand cam cover , on your picture you seem to have just the forward one.
Peter
I also have two breather pipes - the rear one is just not visible in the photo.
My timing belt and water pump is basically due for replacement in any case, so now is as good a time as in six months.
FYI I just did plugs on my car....plug condition were identical to yours....gray with darker bodies. Personally it sure doesn't look to me like you have coolant invading the combustion chamber(s).
You said you did a new radiator cap...just curious if you got the one from one of the big 3 or?
I am struggling / have struggled with the sensor on top; I swapped out the cooling reservoir with 928 Motorsports' aluminum one so had to swap...been a little gun shy about tightening it more...am doing it as incrementally as possible....don't want to break the plastic.
Can you observe the leak in action...is it on passenger side...
The replacement cap is a generic one with the correct rating ( can't remember what it is). However, with both caps I saw the coolant coming from the overflow and the "trail" in my driveway looked the same.
Last bit of information. Putting some engine oil in a glass bottle and holding up to the light shows the oil to be chocolate brown and quite thin. It also smell sweetish.
I would have thought that oil and water won't mix, but perhaps it is the anti-freeze causing contamination.
Last bit of information. Putting some engine oil in a glass bottle and holding up to the light shows the oil to be chocolate brown and quite thin. It also smell sweetish.
I would have thought that oil and water won't mix, but perhaps it is the anti-freeze causing contamination.
Ethylene glycol is an organic compound that takes a liquid form in normal conditions [atmospheric pressure/temperature]- that means it is an "oil". What makes it different is that its molecular structure is highly "polar" which basically means it has an affinity for water. That the molecular structure is "highly polar" means it has a pronounced charge bias- i.e. positive at one end and negative at the other- a characteristic generally not exhibited by oils. Thus the molecule dissolves in water and that is where the fun starts.
When the motor is hot the cooling system is normally pressurised as I indicated in an earlier post however, if the head gasket has blown, oil will migrate into the coolant with the combustion gases and when the motor is shut down the cooling system remains at a higher pressure than the lube system and coolant can work its way back into the engine. The classic signs of this are the formation of a chocolate looking emulsion [sad to say].
Given what we are seeing happen these days when heads are removed, for engines that have no history of head removal there seems to be a strong case for so doing preemptively as it may help prevent more serious decay if the root cause of "the problem" is corrosion driven.
Last bit of information. Putting some engine oil in a glass bottle and holding up to the light shows the oil to be chocolate brown and quite thin. It also smell sweetish.
I would have thought that oil and water won't mix, but perhaps it is the anti-freeze causing contamination.
Forgive me if you've already answered this question, are you noticing oil level visually rising on the dipstick. If coolant is coming from the overflow hose and it's not discolored maybe your car likes the reservoir tank to be a little lower than the "normal" level.
Could also be the generic rad cap isn't holding rated pressure which can cause the overflow condition.. I still suggest getting the correct OEM one. Hold it up to the generic one and its easy to see the difference in build qualities.
I personally replace the radiator cap every spring and I always see improvement in cooling efficiency; I think its one of the biggest bang for buck preventative maintenance measures you can do. Even the OEM one is very inexpensive and you have more assurance the system is running at the correct pressure (and any potential weak spot would be identified earlier). Also; overtightening them can bend the "spring" back too far and again impact the ability for the cap to provide the needed pressure...I've done this.
08-13-2021, 09:10 AM
Now to take it all apart again.
