Slow leak in cooling system.

[elsmandino]

Hi,

I have a rather old (1995) Merc that keeps running out (though very slowly) out of coolant.

I top up the system with new coolant and within a couple of weeks the light comes on to advise me it is getting slow again.

I have tried looking under the car and checked the hoses with the engine running at normal temperature and also left paper under the car overnight to see if I can spot any leakage but neither of these has revelaed anything.

It did occur to me that the pressure valve was faulty, but a replacement has not sorted out the problem.

Is this a common problem with this car and, if so, is there anything I can do about it?

I know that you can get solutions that you can add to the cooling system that can plug any small leaks but I am not sure whether these might do more harm than good.

Thanks

 

[Dec]

You could wait a while, a leak will usually get bigger and then more obvious and so easier to find.
Is it a sealed system (bottle beside fuse box) or an open system (tube open to ground at right of radiator)

Dec

 

[martyz]

If you can't see or find evidence of an external leak,then it must be internal,
Head gasket would be suspect no1.

 

[gegs88]

I think i would be getting the system pressure tested and a dye added to the system before thinking about head gaskets. My local garage charges £35 for a pressure test. Nice and simple and usually tells you a lot. A dye in the system will stain wherever the leak is giving you a better idea of where to look.
If the coolant is leaking on to a hot part of the engine or exhaust it will dry before you can spot it unless your losing the lot in one go.

 

[Jonesy161]

A couple of thoughts out of interest, Is the car getting hot, ie, does the temp guage show an increase from what you would consider normal?

I would also, (if you haven't already), get under the dash and check the heater matrix and pipes, a damp carpet may be a clue but the rate of loss of coolant might not be enough to keep it damp.

Hope you solve it soon.

 

[markjay]

By 'pressure valve' do you mean you replaced the expansion bottle cap (or radiator cap)?

Also sometimes there's a small leak on top of the exhaust so that no liquid is collected under the car.

And obviously there is the dreaded head gasket failure - are you able to check compression, and is there any evidence of mayo in the oil, or oily stains floating on the coolant? MOT gas analyser could help identify traces of exhaust gasses in the expansion bottle.

 

[elsmandino]

Hi,

Thanks everyone for your thoughts.

I did come across something on the net, yesterday, called K-Seal that claimed to fix small leaks anywhere in the cooling system. I am usually reluctant to use anything like it but took the chance in view of the fact that my car is worth so little now and I am relieved to say that it has worked so far - I topped the coolant up just enought so the "low coolant" light went off and it has not come on since.

Early days yet, but hopefully the tiny leak has been sealed up now - fingers crossed.

If it happens again, I am going to start eliminating the problem using your advice above.

I do have another issue with regards to coolant but I think it better to start a new thread for that.

Thanks again for eveyone's help on this.

 

[gegs88]

K seal will find any restrictions in the water galleries of your engine and block em. Also unless your radiator is like new internally the k seal will block it.
Loads of lads use it on a pajero site i go on and wonder why their engines let go after a few weeks.
Some folks swear by it, most think its snake oil. If it was really a miracle cure then every garage in the country would be using it.
Just my opinion though.

 

[Motorvating]

I used K seal and it screwed my cooling system, it clogged it up, so cost me large amounts of dollar. My fault was similar to yours, turned out the block was cracked, so when the engine was cold there was no problem, but when it warmed coolant was able to seep into a cylinder which I didn't notice as it burned off. Over time I started to have problems starting the car as coolant would be in a cylinder, and eventually the coollant system started to pressurise. When it pressurised it acted as if it was overheating i.e. coolant passed by the pressure cap on the expansion tank.