Coolant leak from rear

[BlueQuinn]

I got an orange warning light yesterday to tell me that the coolant level is low, and sure enough it is. The expansion bottle is almost empty.

The temperature stayed just above 80, good oil pressure, no problems driving.
I checked this morning and there's no mayo on the filler cap or dipstick, and I don't think there is oil in the water either.
There was no discernible leaks with the car not started. I started her up and got dripping from the right hand side, rear of the engine. I could not tell exactly where from. It wasn't easy to see anything from the top of the engine, only by looking underneath the car. I can't be sure (I can't remember now if I looked underneath before doing so) but it might not have started until I put the heater fan on.

History time. M104 3 litre engine, aircon needs regassing so it ain't that. The car had a new head gasket 18 months ago, and 6 months ago following overheating and boiling coolant in January I had the cooling system pressure tested and a leak from a seal on the rear left fixed. It also got a new thermostat and a new pressure cap, and since then it's been perfectly well behaved, temperature-wise. Until yesterday anyway.

What is the collective wisdom of the forum?

 

[optimusprime]

info

Put it in to google for more results i did and found my heater pipe was my problem as it goes in to the heater at the rear of engine.

 

[BlueQuinn]

I've not had much luck with Google, but I guess I don't know what the question is I need to be asking.

Lets start with the biggie. Is it likely to be the head gasket?
If it was a head gasket failure, would that result in a single drip-drip-drip or something else more weepy? How likely is it that a year old genuine MB HG would fail with no signs of oil in water, water in oil, water in combustion chamber? On an engine with no other problems?

If it's not the head gasket, what else is there back there? The leak is starting below the exhaust manifolds somewhere as there's no sign of anything above them. Are there core plugs on that side of the block? I gather we have some heater pipes, so that's another candidate. If it's heater pipes, and I don't use the heater it should not drip, right?

 

[Sp!ke]

Is it leaking from around the water pump? Often, it is the waterpump seals that go so that would be on my suspect list as well as looking closely at all pipework and the radiator itself.

I think it unlikely to be a return of your headgasket problem.

 

[Dec]

In the picture below, in Blue, is the general path of the coolant on a W202, yours will be similar, there is a pipe/tube, number 10 / 35 / 30 in picture, it is the likely culprit. Disregard the other text in the picture below as it’s not relevant to your problem.

Some drawings here, see … Mercedes Benz EPC Type W124 124 Information Everything Benz

Dec

 

[kth286]

Assume your left and right side are sitting the driver's seat ?

You previously had a left seal replaced to cure coolant problem, you state.

Under the exhaust manifold is the drain plug and seal for draining the
engine block.

Perhaps that is loose, or the seal needs to be replaced.

 

[a111r]

Not familiar with this model but could you remove the air filter etc and use a mirror and torch to trace the leak with the engine running at operating temp?

If not, then Euromerc might have a quick look as you've spent a bit with them?

 

[BlueQuinn]

Assume your left and right side are sitting the driver's seat ?

You previously had a left seal replaced to cure coolant problem, you state.

Under the exhaust manifold is the drain plug and seal for draining the
engine block.

Perhaps that is loose, or the seal needs to be replaced.

Ooh, that is a very good suggestion. It's in the right place I reckon. Tomorrow I'll have an opportunity to get under the car hopefully.

 

[BlueQuinn]

I finally managed to get under the car, and it is no longer leaking. Blooming typical
Checked the coolant level and it's just where I topped it up to. There is evidence of a some leak from the drain plug though so I think kth286 was spot on.

 

[kth286]

duplicate post

 

[kth286]

Go buy a spare washer from dealer anyway, as insurance in case it leaks again.

Buy two washers, ready for next coolant change in two years time.