Engine dumping coolant... suggestions please

[Nostrodamus]

We have a volvo MD22 P-B engine that will motor for several hours with no problems. Then at some point the about a litre of coolant ends up in the bilge under the engine. It gets there through the overflow pipe which is on the neck of the radiator cap.
I cannot understand why it does it. The radiator cap I would suspect is about 15 years old so the pressure spring may be worn but why do it only after several hours.
It may of course be something completely different but any suggestions would help as I am at a loss.

 

[Cardo]

You're not overfilling with coolant, are you?

If I overfill ours, it usually comes out through the overfill/pressure release and settles at the appropriate level as per the manual.


ps. Not having much luck this season, are we?

 

[LittleShip]

Always difficult to diagnose on here but, it could be

1 rad cap, but IMHO unlikely
2 thermostat, again unlikely as you run for a lengthy period before you get the problem
3 cylinder head gasket. Take off the rad cap when cold and run the engine up to temperature, look for air bubbles coming up to the header tank.

Good luck with fining the problem. If it is the gasket when you rebuild replace the t/stat and the rad cap at the same time.

Tom.

 

[Hadenough]

For a few quid I'd start with, 1) the pressure cap and 2) the thermostat before delving deeper. Although what does it do to coolant temperature when it dumps the coolant? If it stays at normal I'd just ignore it and not top it up.

 

[oldharry]

For a few quid I'd start with, 1) the thermostat and 2) the thermostat before delving deeper. Although what does it do to coolant temperature when it dumps the coolant? If it stays at normal I'd just ignore it.

Only if it does not continue to dump coolant! The header tank or whatever under the rad cap make look full, but if it is caused by gasses from a blowing head gasket, then it will gradullay displace all the coolant, but not necessarily round where the temp sensor is, so that the block may be nearly empty, while the thermostat housing still has coolant in it. I had a car like that once - would dump a lot of coolant, but this would not show up on the temp gauge until things started boiling!

 

[Hadenough]

Yep agreed if it is still loosing coolant it is a different scenario. My experience is that the header tanks often doesn't need brimming mine runs happily with the coolant level about an inch below the top of the matrix and if I brim it it dumps about a litre as soon as it reaches 80degs. Strange though that Nostro's engine dumps the coolant after several hours running.

 

[Nostrodamus]

Thank you for the suggestions.
I don't think I have overfilled it.
I don't have an expansion, header tank so I cannot see anything until after it has happened.
I do notice about a 4 degree rise in temperature when it probably happens.
The scary thing is that when it has cooled down and I look in the cap the water is below the level of the top of the heat exchanger.

 

[vyv_cox]

Three possibilities, in order of likeliheood:
1. Exhaust manifold blocked with salts, backpressure applied to the heat exchanger, O- rings leak, seawater enters coolant.
2. Calorifier tube leaking, fresh water enters coolant, displaces it into bilge
3. Head gasket - highly unlikely.

Try putting a plastic bottle under the overflow from the filler cap. If the problem is simply over filling the excess will be drawn back when the engine cools.

 

[Cantata]

Variation of Vyv's no.1 possibility - hose clamp on upstream rubber boot on heat exchanger needs tightening. Sea water allowed to enter coolant. Symptom on mine was that despite the dump of coolant, the level in the header tank stayed the same. Had me fooled for several weeks.
Downside, having found it, was the time it took to flush all the contaminated coolant out of the entire system including the loop to the hot water tank.

 

[Nostrodamus]

I replaced the coolant a few weeks ago and there is no apparent discolouration or any contaminates.
The amount found in the engine bilge approximately matches that drained out of the system. With no header tank the only way to add extra coolant when under way is to stop the engine for a good while in order to remove the filler cap.
Exhaust water seems to be coming out normally and I have just renewed the impala and raw water pump.
I will go through the suggestions mentioned but at the moment I am stumped.

 

[wiggy]

Had exactly the same problem on VP2020. Eventually overheated, and temporarily seized. Turned out that the boot on the front of the engine was not seated properly and was allowing salt water into fresh system. I've had it removed and striped, thermostat destroyed, one piston burnt and barrel marked, 2piston won't hold thin oil on top.
Great start to the season.

 

[Nostrodamus]

Things could be worse but I doubt it. It would appear I am also using excessive oil but no idea why or where it is going. We have always burnt oil but I don't know why.
The engine always starts first time every time. Runs smoothly and well. There in no contaminates in the oil or water and no oil under the engine. I am just at a total loss apart from knowing this could be serious and cost money we don't have. The water problem could be related or not, I don't know as both problems did not start together. The oild problem has always been there but now it seems to be using a bit more.
Looks like a lot of anchoring this year until I can get back into a marina for winter.

 

[sailorman]

Things could be worse but I doubt it. It would appear I am also using excessive oil but no idea why or where it is going. We have always burnt oil but I don't know why.
The engine always starts first time every time. Runs smoothly and well. There in no contaminates in the oil or water and no oil under the engine. I am just at a total loss apart from knowing this could be serious and cost money we don't have. The water problem could be related or not, I don't know as both problems did not start together. The oild problem has always been there but now it seems to be using a bit more.
Looks like a lot of anchoring this year until I can get back into a marina for winter.

Try a 20/50 nxt oil change

 

[Cardo]

The scary thing is that when it has cooled down and I look in the cap the water is below the level of the top of the heat exchanger.

Different engine of course, but our coolant level settles at 1" below the filler cap, which is below the top of the heat exchanger stack.

 

[Nostrodamus]

I just filled mine to about half an inch below the top of the filler cap. I then ran the engine for about five minutes before it has chance to build any pressure up or get too warm.
Just took the cap off again and now the level is up to the radiator cap. !!!
Anyone know the correct level to fill it to on a volvo MD 22?

 

[Cardo]

I just filled mine to about half an inch below the top of the filler cap. I then ran the engine for about five minutes before it has chance to build any pressure up or get too warm.
Just took the cap off again and now the level is up to the radiator cap. !!!
Anyone know the correct level to fill it to on a volvo MD 22?

Is your heat exchanger stack leaking?

 

[Nostrodamus]

Is your heat exchanger stack leaking?

Don't think so but it looks as if I am going to have to take it all apart and clean it in winter unless I have to do it before.

 

[vyv_cox]

Under normal conditions the pressures in various parts of your water systems are:
Fresh water about 20 psi dependent upon the pressure switch fitted
Coolant around 12 psi dependent upon the cap
Seawater nominally atmospheric in an open ended system.

So if there are any leaks anywhere they will go from high pressure to lower, but not the opposite. However, many Volvo engines accumulate salts in the exhaust manifold that can increase backpressure in the seawater system until it exceeds coolant pressure. There have been many examples on this forum in which the seals in the heat exchanger have given way under this reverse pressure, driving seawater into the coolant which overflows into the bilge.

The first, easiest and cheapest thing to check is the manifold, just a matter of taking it off and cleaning salts out carefully. Don't attack it with a screwdriver as many have driven theirs right through the walls. With luck that will fix it but sometimes the seals are displaced in the heat exchanger and need to be put back in place.

If coolant does not leak when the engine is not running it is probably not the calorifier. If coolant is found first thing in the morning when the domestic water pump has been switched on all night it is almost certainly the calorifier coils that are perforated. I have known three of these in the past couple of years.

 

[Nostrodamus]

Thank you Viv and all those who have tried to help.
The only time anything ends up in the bilge is after the engine has been running a while.
I have tried draining some coolant off so it is now about an inch below the filler neck but still covering the heat exchanger and ran it up to temperature and across the bay.
So far it actually seems to run a little cooler and there is nothing in the bilge. It may have been that I was overfilling it and as there is no expansion tank the only way the liquid could go was out the pipe at the side of the filler cap and into the bilge. I do agree with you about the elbow and I imagine it does need a clean. When we are somewhere secure I will do it.

 

[PhillM]

I had a problem where the jubliee clips on the return pipe had got a bit loose.

On tick over no problem. At 2000+ revs it leaked coolant into the bilge.

Long shot and I'm sure you will have checked but 5 mins with a screwdriver checking the clips may be useful. Worse case you eliminate another possibility.