thermostat housing leak again !

[jpliddy]

hi all
its been a while now but my thermostat housing has decided to leak again the leak is small as its just got staining down the engine block,
did the d24s ever have a gasket the flat mating surface ? , last time it leaked a while ago i used hylomar blue its lasted probably a couple of years nearly i think i just don't like to see any staining on the engine block ,
i have seen a gasket supposedly for volvo d24s and petrol engines too on ebay !
do you have any suggestions on this subject , regards jim

[v8volvo]

Interesting issue. Did you replace the O-ring behind the thermostat housing when you repaired the leak last time?

There is no flat gasket used on this location -- just the O-ring. A new thermostat always comes with one.

If repeated leaks are an issue and O-ring replacement doesn't seem to be fixing it permanently, I wonder if you have a problem with pitting of the aluminum t-stat outer housing? If you take it off, does the mating surface appear flat and smooth where it meets the O-ring?

[ngoma]

Agree, either pitting or rough mineral buildup or both.

[v8volvo]

Originally Posted by jpliddy

i have seen a gasket supposedly for volvo d24s and petrol engines too on ebay

Only further comment on the above note is that the Volvo petrol engines are completely different in design from the diesels. So if there is somewhere that you are seeing someone say they have a gasket that works for both petrol and diesel models that would be WRONG, not possible as no components or systems are shared and there is no parts compatibility or crossover whatsoever. And it is probably for the petrol engines only. Application catalogs for the diesel models are notoriously inaccurate and often do incorrectly list gas engine parts as applicable for the diesels. One place I was shopping for parts one time even offered to sell me a nice Bosch ignition coil for my diesel Volvo, if that tells you anything.

Most of the Volvo gasoline (petrol) engines have O-ring type thermostats too but I believe there are paper gaskets available for them as an alternative. So that may have been what you saw.

The D24 family engines don't have any flat surfaces where a paper gasket could be used on the tstat housing so the proper factory style O-ring seal is the only answer for them. Unless you want to resort to RTV silicone sealer. In the event that your aluminum housing is pitted badly enough to compromise the seal of the normal rubber O-ring, and if you have trouble finding a replacement housing, careful and very limited use of silicone sealer in combination with a fresh O-ring could be a solution to fill the spots where pitting is creating openings. The downside is you want to be sure to not spread any inside the engine as it will clog the radiator and heater core if it gets free, use it only on the external sealing areas and only in limited amounts..... And it will also greatly increase the irritation and labor factor the next time you ever need to remove it, as it will involve cleanup of old sealer to reassemble. So this is an approach best avoided if you can make the factory sealing system work for you. But it's a route you can take that will succeed if other options are not workable.

[jpliddy]

hi all
i am monitoring the leak its not a lot , but some dried weeping marks on engine block, the outer edge of the housing has a type of lime scale look its probably been building up a bit over the years not horrendous but its there , i put some hylomar sealant on the mating surface when i charged the thermostat few years ago now, perhaps i was a little generous with the sealant i remember cleaning the surfaces with very fine emery paper and drying the area ,so when i get time i will do the job again ! how often do you change the thermostat too?

[ngoma]

Oh ok, so no actual coolant dripping? Just some slight discoloration? Then just keep it under observation. No need to dismantle anything-- chances are that could even make it worse or at least turn it into a big job for nothing.