W124 blowing coolant

[Mercky]

Hi There!

I have a W124 320 coupe, on two occasions (months apart) the feeder pipe that runs from the top of the rad to the coolant reservoir has blown off, resulting in overheating and pressurised coolant been spashed all over the engine bay. What happens is the snap on type fitting on top of the rad blows off, obviously under pressure. The first time it happened my mechanic reckoned it was just loose so he refixed it adding some epoxy to ensure it dident come off again...........well it did, epoxy and all, so there must be a build up of either air or water pressure in the system. The last time it happened the I was not in traffic and only 10 mins from home so the engine would have been running quite cool...........anyone got any bright ideas? It's really annoying as the coolant is fairly corrosive and last time I had to change a belt as it had become contaminated and squeely as a result.

cheers
Mercky

 

[MondeoMan]

I'm thinking head gasket failure. Does the oil and coolant look clean?

 

[Mercky]

w124 coolant

yes, both oil and water appear clean. The snap-on fitting on top of the rad almost looks like it's designed to pop off in high pressure situations....why did merc no put a jubilee clip here like everywhere else? just a thought.
The car has only 50k up and otherwise runs very well.

 

[spannerman]

Mercky,

Take rad cap off, and bring the revs up high. Look to see if there is a lot of air so bubbles coming up, or worse still does the coolant come out all over the shop? If so MondeMan is right and head gasket is gone. If not check that the rad cap is the right pressure for the system....there will be a figure representing PSI on the cap. Perhaps smeone changed it and didn't fit the correct pressure cap, or if it corresponds maybe the spring-loaded plunger with the rubber gasket, designed to close off the rad below the intake pipe (that you're talking about) has weakened. I'm still thinking head gasket gone, or going, between a cylinder wall and a water port, thereby pressurising the sytem.
If you have a torque wrench you could try torqueing all the head bolts in proper sequence WHEN THE HEAD IS STONE COLD and you just might get away with it.
It's worth a try, no expense, before you start on major surgery.

Donie

 

[Mercky]

w124 coolant

Hi Donie,

thanks for that........there is no filler cap on the rad....do u mean on the reservoir? It does have a spring loaded cap. If it was the head gasket would this not be happening all the time?

M

 

[tom7035]

Hi Mercky.
I go with spannerman and Mondeoman - head gasket, but you could try a pessure test on the cooling system, this would confirm it.
Tom.

 

[spannerman]

Mercky,

Sorry for the confusion, yes the cap is on the reservoir, and if it's pressure rating was too high it would allow over-pressure to build up in the system.
Don't hold much hope of this being the case. Cap should be somewhere in the mid teens PSI

I'm puzzled as to why the mechanic decided to use epoxy-resin on the pipe, and not a small jubilee clip, as would be customary. Perhaps you should fit a jubilee clip first and see what happens.

You don't mention if the temperature goes into the red or even rises considerably, before she disgorges her coolant. ??

Donie

 

[Mercky]

w124 coolant

well the first time it happened back in May i noticed it because one of the belts had become squeely and i opened up the bonnet to see what was going on, i noticed some liquid around the place and then noticed that the fitting on top of the rad had loosened but not actually popped off....this was the source of the liquid, i just fixed it back on and everything was fine except i had to get a new belt fitted, there was no increase in temperature whatsoever at this time, probably because i caught it before all the coolant leaked out. This morning whilst driving i suddenly noticed that the temp gauge was very high...not in the red but way above normal, i pulled over and saw coolant everywhere and the fitting on the rad had popped fully off. This fitting kinda snaps on and is held by 2 light plastic grips, not very robust looking and in my opinion would pop fairly easily. Why would it happen as intermittintly as this? There is no mayonnaise in reservoir or oil and car normally runs nice and cool. i often drive it in heavy traffic where it would run hotter (particularly in recent weather) but no problems occur and temp stays normal

 

[spannerman]

Mercky,

If you're still in trouble there a great guy out around Shankhill, Bray, called Terry Jackson, and as regards Mercs he's probably forgotten more than most of us will ever learn. Look him up and give him a call. He's a real good guy.

I'm still thinking 'torgue the head' and try a change of thermostat, but also do something about that reservoir-to-rad pipe. Afterall it supposed to be able to hold onto at least 13-14 PSI and if it's ready and willing to pop off at the drop of a hat that can't be a good start.

Donie

 

[Mercky]

w124 coolant

Thanks Donie, yeh I know of Terry Jackson. I use Greenmount Motors but I'll keep terry in mind. I think it's just the fitting - it comes off really easily so maybe with a bit of pressure and a pothole it just flys off.

Thanks to all who replied

Mercky

 

[mjtray]

Merky,

One sure fire way to test for a blown head gasket on the M104 engine is as follows,

Start car from cold and immediately go and squeeze the top hose leading from the top of the radiator to the thermostat......its should be soft and squishy. If it hard and full of pressure your head gasket has blown and exhaust gases are building up in your coolant system.

The little elbow bend that fits into the top of you radiator, ie the bit that got blown off has a small "O" ring located on the elbow....this normally gets blown off when the elbow gets blown out of the top of the radiator. Make sure that this is replaced otherwise it will always be loose,weep, and blow out coolant

When this happend to my M104, the cause was an airlock in the coolant system that was stopping the coolant from travelling around the system and the only way for the pressure to go was out of that little elbow joint.....this happend to me on top of a French Alp on a scorching hot Sunday afternoon miles from anywhere.....nice!!! Try draining and refilling the coolant system.....make sure you have your heater dials set to max heat otherwise you risk further air locks forming.

Hope this helps.

 

[spannerman]

Good stuff mJtray,


That sounds like good solid advice........and ain't it a fact that you can't beat the voice of experience.

All too often we don't consider airlocks. We just fill the sytem and expect the water-pump to work miracles, and while most of the time it does on most systems, it doesn't necessarily mean that it will do all the time.

Donie