Disappearing coolant

ms500

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My car seems to be losing coolant, the first time I checked the expansion tank after buying it it seemed empty, so I filled it to the line with a 50/50 Anti-freeze/Water mix.

I still seem to keep having to add coolant on a weekly basis, the level drops by a couple of centimeters per week.

I can't see any leaks and there are no puddles under the car. The car has never overheated, and there is no white smoke from the exhaust. There is no oil in the coolant or vice versa. The radiator is fairly new and is in good condition.

I can smell anti-freeze from the general area of the engine bay when stood outside the car when the engine is running, and also through the interior air vents, so I guess there must be a leak somewhere.
 

Will

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It's probably the head gasket. My reasoning being:

1) 300-24s are prone for it
2) Your car has a low compression problem
3) It's losing coolant

I'd definately get it checked out properly as you need to know where you stand with this car. If the CHG is leaking and it's left as it is, it could cause further problems in the long run (eg bore wear)

Obviously could be something less serious such as a leaking water pump, but I reckon you'd notice that quite easily. Head gaskets seem to be quite a weak point on these engines from what I can gather.

Will
 

bolide

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I'd say water pump

In order of occurrence due to age, I'd say W124 water leaks go like this:

1 - radiator leak (normally a tiny, tiny pinhole)
2 - water pump
3 - black plastic elbow on the top of the rad
4 - cylinder head gasket
5 - cracked or leaking header tank
6 - heater- or duovalve-related problem

I've seen a few cars when the water pump has been replaced more than twice. But I've also seen 200k cars with original water pumps. By contrast I rarely see older cars with original rads

Nick Froome
www.w124.co.uk
 
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ms500

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It's probably the head gasket. My reasoning being:

1) 300-24s are prone for it
2) Your car has a low compression problem
3) It's losing coolant

I'd definately get it checked out properly as you need to know where you stand with this car. If the CHG is leaking and it's left as it is, it could cause further problems in the long run (eg bore wear)
But wouldn't that result in white smoke, loss of power or oil in the coolant? I don't seem to have any of those, and the fact that it can be smelt by the engine bay would suggest an external leak to me.

I also checked for bubbles in the expansion tank (sign of head gasket) when the engine was running, and I didn't see any.

I think I probably messed up the compression test by not having the throttle open.
 

Will

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But wouldn't that result in white smoke, loss of power or oil in the coolant?
Not always. Depends on which way the gasket has failed. Some can leak oil into the coolant, some can leak coolant into the cylinders, etc.

Some may overheat dramatically, some may not.

If it's a slight leak, you're not likely to notice plumes of white smoke or a significant power loss.

I'm not saying it's certainly this at fault, just that it wouldn't be an unusual or unexpected failure on your car, and combined with the other issues you've mentioned, it's surely worth ruling out?

Will
 

Dieselman

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With a HG failure into the cylinders you would normally see steam on start up and maybe a bit of hydraulic locking as well.

The fact that you can smell antifreze says this is an external leak. It's possible that you can't see the leak as it is coming out as steam. Check after it's been off for a while and wipe your finger around various places such as pump and thermostat housing to see if they are wet.
 

imadoofus

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This and that.
I had this with my 320, and it turned out to be a hose into the nearside rear of the block.
 

panason1c

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If you can smell coolant then its definately a leak, ......check all hoses.
 

Adam230K

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If the head gasket is in question wouldn't he see some whiteish foamyness on his oil cap?
 

imadoofus

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This and that.
I suspected my head gasket too, but there were no other symptoms. In the end, as I said, mine turned out to be a minor problem and an easy fix.

If only I could say the same for all the other stuff... :(
 

Leemc2008

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Check your water pump.. see if you can see it leaking around the gasket at the bottom..

Mine went here..
 

Ade B

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Perhaps a silly question but is water pump failure a mileage or age related thing?

Ade
 

Dieselman

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Bit of both really, combined with engine revolutions and anti corrosion quality.
 

Vlad

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Also check at the rear passenger side of the block...hard to see as the inlet manifold gets in the way, but if you use a strong torch and then look at the very rear of the block, there is a water pipe that goes into the block and the O Ring can perish and result in lost coolant........make sure you look after you have taken the car out for a decent run and once it is up to temperature....if its leaking the block will be damp with coolant.
 

imadoofus

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This and that.
Vlad said:
Also check at the rear passenger side of the block...hard to see as the inlet manifold gets in the way, but if you use a strong torch and then look at the very rear of the block, there is a water pipe that goes into the block and the O Ring can perish and result in lost coolant........make sure you look after you have taken the car out for a decent run and once it is up to temperature....if its leaking the block will be damp with coolant.
So at least somebody agrees with me...;)

The other trick is to remove the engine undertray. Then you can see where, in relation to the engine, the water is driping
 

Dieselman

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The other trick is to remove the engine undertray. Then you can see where, in relation to the engine, the water is driping
Just got to get under the car for that, but this is where the Wife can help. No need for ramps .:devil:
 
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ms500

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I'll get the water pump checked out, and remove the sump guard to check for drips. Of course the rain doesn't help when looking for water leaks.

I hope I don't have head gasket trouble, although there is no record of it being replaced in its 204,000 mile history, just the mercedes stamps in the book, some suspension stuff, a new radiator, and tyres.
 

Vlad

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I would be amazed if its got that far without a head gasket change....with that in mind, I would be looking at the other options first......a quick check on a blowing head gasket is to start the car from cold and squeeze the top hose coming out of the radiator. If its hard its got exhaust gases getting into the system from a break in the head gasket and/or you may find traces of oil in the expansion tank.
 

Brabus3.6

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I vote for the headgasket (but then again I would :rolleyes:). Do you notice the car running slightly rough at first start up after it has sat for a few hours as the water burns off? Feel the radiator top hose as Vlad suggests, mine is always under pressure (hot or cold) once the hg goes.

My fire ring has given out before allowing water straight into the combustion chamber without oil polluting the water or vice-versa. The best test for it is to test for combustion gases in your cooling system; any garage should be able to this for you if you want to be sure.

If it's the hg be sure to change the valve stem seals and have the valve guides and head inspected.
 

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