Slow Coolant loss

[Slowtack]

My W124 E300 diesel looses coolant slowly, no visible leak, pressure test OK. If I loosen the pressure cap the leak stops completely. Engine temperature guage reading OK, about 85 degrees. Coolant is clean and shows no contamination. Any thoughts?

 

[Ultymate]

You have a small leak somewhere under pressure, if you can't see any obvious leaks in the engine bay check for wet mats inside the car you may have a leak in your heater matrix. Best bet is to get the system pressure tested this involves pressurising the system with a pump via the expansion tank and looking for leaks whilst under pressure.

 

[malcolm E53 AMG]

I have used this highly recommended product for a small niggly leak that could be anywhere in the coolant system. Coolant loss was about 1 litre every 500 miles or so. No visible leaks from rad or water pump etc so decided to use Ksealit and everything is back to normal.

http://www.ksealit.com/k-seal-98-p.asp

 

[Parrot of Doom]

Look behind the engine, between the engine and the firewall. There are coolant pipes there. Thats where mine went - rust.

 

[Slowtack]

Thanks all. Pressure test was OK. Will take a look at those pipes before looking at the additive.

 

[wireman]

WATER PUMP

Check around its nose behind the pulley there are drain holes which will be damp or drippy.
With the engine hot any damp will dry off and you will be hard pressed to find any leak so do the check once its cooled down, don't depressurise it, have a look and feel at the drain holes.

Often water pump glands only leak whilst warm and stopped.

I have seen many cars with this fault and the most common outcome is total failiure of the gland leading to horrendous water consumption and in one case total loss of a Jag engine because the dealer was to tight to fit a pump under waranty.

Beware of man with leak cure in tin. Any small waterways can become blocked if the water flow is cut off them, often these are the water ways in the heater matrix and mine like many others gets shut off for summer.

 

[Aussie Nick]

If you find the hole come back to me .I have a tried proven and inexpensive method of providing a good seal which does not involve welding or running a chemical through the system.

 

[David Nock]

If you find the hole come back to me .I have a tried proven and inexpensive method of providing a good seal which does not involve welding or running a chemical through the system.

and not organic human chemicals?

 

[Aussie Nick]

Ha .ha ha. I like your style. Maybe that would work too. I wonder what senior member Bitch will say about this.

 

[Bolide]

My 250Td sprung a leak at about 190,000 miles. It was a very, very tiny pinhole in the rad and it only leaked as the car cooled down

Suggest you put newspaper under the car after a run and locate the leak by finding where it drips from

Obviously if it leaks only with the cap on it leaks only under pressure. So not much of a leak

I think all original W124 rads will need replacing by about 250,000 miles / 15 years

Nick Froome
www.w124.co.uk

 

[Ultymate]

My 250Td sprung a leak at about 190,000 miles. It was a very, very tiny pinhole in the rad and it only leaked as the car cooled down

Suggest you put newspaper under the car after a run and locate the leak by finding where it drips from

Obviously if it leaks only with the cap on it leaks only under pressure. So not much of a leak

I think all original W124 rads will need replacing by about 250,000 miles / 15 years

Nick Froome
www.w124.co.uk

The cap itself could be leaking and losing small amounts of coolant via the leakoff pipe. You can get the cap pressure tested but to be honest for what they cost just as economical to relace yourself as to get it tested by a garage unless you have a really tame one, garage that is

 

[Slowtack]

Ive already replaced the radiator at mechanics suggestion - no change, pardon the pun.
Thanks again all for the advice. Cannot see visble leak anywhere, even under pressure. Will take closer look around the pump.