coolant loss leak

[Davezj]

this i an information thread for others to use, it is a a problem and fix. i will try and keep it simple. i am not saying this will always be the case but it is worth checking.

Problem:-
when the hot weather hit i noticed the expansion tank was empty, i checked the radiator and there was no water visible.
the temp gauge on the dash was reading slightly above the normal level by as little as one notch on the gauge.

diagnosing the issue:-
i filled the radiator back up with about 2L of water. and filled the expansion tank.
i checked the radiator and hose system and water pump area for water leaks, or signs of dried coolant stains, there were none visible.
i went for a run out about 5 miles the engine did not over heat but went to the same one knotch above normal temp.
checked water level after trip out, expansion tank looked full, let the car cool down and checked radiator, there was no water to be seen.
topped up the radiator again with 1L of water.

i repeated this a few times and each time coolant was lost, about 1L, but the expansion tank level never got drained as it should do if the radiator needs more coolant top up.

Fix:-
top up the radiator.
Change the radiator cap for a working one (i happen to have one in the shed).

i can not see any physical damage to the old cap and seems to squidge up and down like the new one.


well the good news is the problem has gone away, so all of this is due to a dodge radiator cap.
it must be something to do with maintaining the pressure and seal in the radiator to expansion tank link.
i don't actually know where the coolant has gone each time i filled the radiator up. it must have come out from round the radiator cap, but i did not see any steam or any staining round the cap.
just to note i deliberately filled the expansion tank with just water and now it smells of coolant, so i know the expansion tank is filling and then giving back coolant to the radiator when needed.
i have checked the oil cap and no gunk in there, and there is no steam out the back, so i happy it is not a head gasket issue either.



hope someone find the useful.

[BraindG]

Good tests there Dave, bit weird that the previous cap wasnt showing signs of aging or damage yet with the one from the shed no further water loss - would make it hard for others to diagnose?

[Davezj]

yes it would be tricky to diagnose if you didn't have a known working cap.
you would have to borrow a known working one from a mate.

there are other threads on here that have come to this conclusion about rad cap failure in round about sort of ways with lots of waffle inbetween the interesting posts.
so i thought i would put everything you need to know in the first post of this thread.

[elnevio]

Believe it or not, you can get the correct 0.9bar Mitsi rad cap from Halfrauds for about a fiver.

Makes it a relatively inexpensive check!

[MarkSanne]

What a coincidence! Yesterday I drove my neighbour to his workplace to do some fiddling with cars. While I parked I let the engine running and about a couple minutes later... tempurature was 2/3 notches higher than regular centre?!! Expansion tank was empty, and nearly 2L of coolant went into the radiator. After that, everything was fine again. I have no idea where the missing coolant went. No sludge in the oil, no marks of coolant leaks anywhere. Mysterious. But I'll monitor it closely and if indeed a new cap can be bought for next-to-nothing I'll def do that too, so thanks for the tip / sharing Dave!

[Louis]

I reckon 2 litres is a lot to loose through a rad cap with no sign of leakage!.
My antifreeze is blue and when i had a minor leak at the small pipe from under the cap (the one that goes to the expantion tank), i could see the marks of dried antifreeze!.
It is possible the if the fluid is mostly water it would evaporate as it leaks and not leave a trace, but the antifreeze would leave dried marks.
It depends how much you are lossing over how quick a time period.
I.e. 2L in a day with no signs of leakage, i would be looking elsewhere.
2L in a month then possibly evaporating from cap leak (but should show signs of dried antifreeze).
2 litres is a lot of fluid to dissapear with no sign of leak!.
Hopefully you are right and the weak spring or badly fitting cap is the problem, and it is an area where a leak evaporating may not be noticed, but keep an eye on level and update if the new cap has def sorted prob.

[mike74]

If its was the same as my cap went then, the fluid would have been pushed past the cap & out of the expansion tank overflow onto the ground. My cap was so bad that you could squeeze a coolant pipe & hear the fluid squirting past the cap into the reservoir!
Brace yourself for a split radiator/pipes soon though!

[Louis]

usually when the pressure against the cap raises the rubber, pushing the spring up, then the first escape for the fluid is through the overflow pipe to the expansion tank and then out through the expansion tank overflow, so fluid would be exiting there out through the overflow hose. (as in your first post)

The expansion tank is not always going to suck the fluid back in as when the cap is sealed the hose to the expansion tank is blocked off. it is only open when the cap is raised due to pressure and allows fluid out.

The loose cap will allow the coolant to boil. (a higher pressure cap raises the boiling point of the coolant, so the reverse is also true a lower pressure or weak rad cap would allow the coolant to boil)

Keep an eye on it and see if it fixes the issue.

[Davezj]

i always thought as the coolant coolder down and shrank in volume some of the coolant in the expansion tank went back in to the radiator, to fill the void left be the cold coolant, but now you explain it like that louis it does seem that once the coolant cools the cap will be slamed shut by the spring in the cap so no coolant will be able to get back in the radiator.

on the other hand if the coolant does not get sucked back into the radiator from the expansion tank, why is the expansion tank ever empty, is it natural eveaparation due to engine bay temperatures, but that would need the expansion tank cap not to be on the top of the tank correctly. i don't think the coolant in the expantion tank can evaparate due to the configuration of the inlet and overflow pipes. i suppose if the coolant started to boil then it would force it's way out of the overflow. but then i would have thought iwould have seen the temp gauge hit the roof.

i did check where the expansion tank overflow goes down behind the engine mount and there was no evidence of a large coolant leak down there.


i will keep an eye on it for a good few weeks to come as i don't want to loose the engine due to a coolant leak.

[Louis]

Water from the expansion tank will go back into the radiator (it will get sucked back in) until the cap spring closes the opening for the expansion tank hose. It is possible for the full contents to be taken back into the rad before the cap shuts.

If water was leaving due to cap raising, it would go to the expansion tank before it leaked from the cap itself.

[quote] i will keep an eye on it for a good few weeks to come as i don't want to loose the engine due to a coolant leak. [quote]
It could be nothing, but just worth mentioning so you can keep an eye on things.