Compression Test / Coolant loss ??

[Philbask]

Hi all,

M102 W124 230CE, losing coolant (about 3-4 pints per week!) I have looked when hot, when cold but can see no obvious leak, reasonably new radiator, thermostat plus housing and expansion tank cap. Also when I go to top up, invariably there is still pressure in the system.

I did a compression test, all cylinders at 9 Bar, (oddly manual says 7.5?), however spark plug 4 was tight to remove and discoloured.

Now I know remote diagnostics is more than difficult...... but with the wealth of experience here, would you think head gasket irrespective of the compression test results?

Car runs fine by the way

Cheers, Phil.........

 

[190]

If it was the head gasket wouldn't that show up in the condition of the oil i.e. mayonnaise.

I've seen the same problem with No4 plug nearest the bulkhead and assumed it was because the cold start injector is at that end of the inlet manifold. This was only after high mileage on that plug and new ones were fine.

 

[Philbask]

Hi 190,

No water in oil, I'm assuming if it is gasket that it would be blown from water channel to cylinder... I'm just thinking that it's a fair amount of water to loose without any visible signs??

 

[optimusprime]

Phil have you felt the back of engine where the rocker box is fixed to the cylinder head. Let us know if you find water in this area .

 

[Philbask]

Hi Optimusprime... Ran the car about 3 hours ago and just gone out to have a feel around... it's a little oily in that area but I'm pretty sure there is water there also, had a look from the oil filter side and there is definitely damage (a split) to the heater hose coming off the head, so that's the next item to get on order ! Thanks for the pointer mate

 

[merc85]

Are the carpets dry inside the car, just thinking maybe a heater matrix.

 

[Philbask]

Yeah carpets dry, no signs of water inside the car, and by the amount I'm losing it would be swimming ! ;-)

 

[merc85]

Yeah carpets dry, no signs of water inside the car, and by the amount I'm losing it would be swimming ! ;-)

Just a thought its got tobe going somewhere, cracked block perhaps only visible when the car is hot as the crack opens up?

 

[DavidL]

Any odd marks on the exhaust/manifold? I've seen occasions where the leak sprays straight onto the exhaust and goes up in steam so you never see it.
You can test the coolant for exhaust gases which is more reliable than looking for mayonnaise.

 

[bolide]

You can't assume anything with cylinder head gaskets. They can fail in a number of ways. The classic failure, not that often seen on Mercedes engines in my experience, is when the exhaust gases blow the water out of the cooling system. That's a combustion chamber to water channel failure in the CHG

Have you checked the gearbox oil? The radiator has channels for the gearbox oil

Have you checked under the car when it's been standing? Try putting dry newspaper under the car when you park it and checking it 30 mins later. This may give you an idea where it's coming from

My money is on a water pump leak or a split in the radiator

Nick Froome

 

[grober]

If its not the water pump then try the coolant headspace test. Use an exhaust gas analyser probe to test for combustion gases in the headspace above the coolant- non invasive very sensitive test. Bore scope [ cheap on ebay DBPOWER USB HD Borescope 2 Million Pixels CMOS: Amazon.co.uk: Camera & Photo ] or even just a torch shone down the spark plug hole--- if coolant is leaking into cylinder the top of the piston will look "oily" --- its not its a mixture of water and carbon from cold running
ps the M102 engine is well known for cylinder head gasket weakness

 

[Will]

As above, will almost certainly be the head gasket. I have done several 8v M102 engines before - they always tend to go at the back starting at cylinder 4.

If you keep topping the coolant up the head will become badly corroded - scrap engine time.

If you do the head gasket at the first hint of trouble, it's less than £100 in parts and consumables and a day's labour for a decent garage. Get new plugs, oil and air filter fitted - no labour for those. The cooling system will probably want a good flush though.