Coolant loss

On my Discovery 3.5 V8, I need to top up my coolant about once a week with at least half a litre! There are no obvious leaks and I've put a good stop leak in too. When I start it after it's been standing for a good few hours it has a misfire for a short while,then clears. Could it be a slight head gasket leak into one of the cylinders?

I've had three 3.5efi RRC's & experienced similar symptoms on one of them. The misfire from cold could well be a damp plug from leaking coolant into the cylinder, which then fires as the engine heat dries it out. When removing the expansion tank cap, after the car has stood overnight, do you get a significant pressure release? Also look out for a raised engine oil level & signs of coolant mixing with it.

Sort of what I was thinking with the misfire. The oil level is ok, and not contaminated which is good. When I first had a misfire the other month, it was due to the ceramic on one plug being damaged-and it was a fairly new plug. I checked all the plugs the other week when i had the misfire again and all ok. I've got magnecor leads on too. Also,it doesn't matter if it's on petrol or lpg so not fuel problem. I have thought of leaving it overnight,taking out plugs in morning,turning it over and see if water shoots out of any of the bores.
Haven't checked expansion tank,but will do later as haven't used today yet.

If anything in the engine it's OK can be the heater radiator. Mine only consumes some water during winter, in summer never needs to fill the level. I assume it's a small hole somewhere on the heater but when thinking in take apart all the dash....simply fill in the expansion tank.

skunk98 said:

On my Discovery 3.5 V8, I need to top up my coolant about once a week with at least half a litre! There are no obvious leaks and I've put a good stop leak in too. When I start it after it's been standing for a good few hours it has a misfire for a short while,then clears. Could it be a slight head gasket leak into one of the cylinders?

Click to expand...

Do a compression test. Also have a good crawl around under the motor and look carefully at your core plugs. Stop leak can lead to problems, be careful with it.

My old motor held pressure in the tank overnight, over a week, everything, but never lost a drop.

My new engine does not hold any pressure but doesn't lose a drop either.

Explain that one.

Got my mate to do a 'sniff' test on it and all ok! I'm starting to think heater matrix as in a week, expansion tank has emptied. Won't be investigating that anytime soon though,I'll wait til the warm weather again...if we get any!