Mysterious coolant leak

So it’s an L322 4.4 V8 BMW Petrol engine- sentimental so despite age, scrapping is not an option.

Going through coolant every 3-4 weeks with the low coolant warning coming on. Pulled into a garage last week for them to top it up after short 5-10 min drive and coolant boiled out of the reservoir like lava. The temperature gauge never moves above normal.

Done a sniffer test twice for the head gaskets and it’s fine and no signs of coolant in the oil.

Drove it to a relatives 150miles with AA cover in place, the fans on full heat into the cab and windows open. It drove like a dream and no coolant lost.

No warning lights on the dash. But if I do a short 10 min journey without the heating on full she burns through coolant and smells like I’ve driven to France and back.

Mechanics a bit baffled. Any Rangy expert thoughts appreciated.

Poss the common leak at the back of the engine left hand side as you look at it there is a push fit connector. It leaks down the back of the engine and evaporates so hard to find its a cheap part I always carry 1 in the car.

biketeacherdave said:

Poss the common leak at the back of the engine left hand side as you look at it there is a push fit connector. It leaks down the back of the engine and evaporates so hard to find its a cheap part I always carry 1 in the car.

Click to expand...

Thanks but out of interest if it was a leak wouldn’t it leak all the time regardless of when the heating is on. As it drove 100+ miles last weekend heating on full blast to pull heat away from the engine and no coolant loss as a result. Sadly I can’t drive with heating on full whack year round.

You can't use the temperature gauge for anything useful.

For one thing - they ONLY works if the engine is full of coolant - once the sensor isn't IN coolant, it move change anyway... That goes for all cars.

You might also need a better mechanic - it's not usually very complicated on these to find a leak. The hardly ever do headgaskets, but if you keep driving it without coolant, it can occur.

If you don't see a pubble under the car anytime, it's probably loosing it while moving along, suggesting it's heat/pressure related.

The other issue with the BMW M62 (and my experience is with the BMW's, but I understnad it's no different in the L322), is it will show "Normal" right in the middle, from 75C to 120C (probably the same for ALL L322s, to be fair).

The M62 runs a 110C mechanical thermostat and it's MAP-Controlled, so the engine ECU can heat the wax pellet to force the temp lower than that. If the Thermostat heater fails, it'll raun at 110C all the time, even when it shouldn't. It will log a fault code, but will NOT turn on the check engine light.

So, running with the heater on, reduces the coolant temp, as more heat is pulled out fof the system. The most liekly places for leaks are going to be a plastic part somewhere, like a junction or the radiator end caps (or even the alloy core). The valley pan gasket can leak (take the engine cover off and look under the intake manifold), and there are some hoses across the back of the motor too, plus the "crossover" pipe. Most of the junctions have o ring seals and they can go hard with age, not sealing as well. Some things will leak from the extra pressure of getting hotter, but some can leak as they expand from the heat.

You can get UV dye to go in the coolant, but coolant generally leaves a trail where it's leaking out anyway - a bt of a crust of dried coolant builds up.