Volvo Penta MD5A cooling problem

[cborden689]

So i recently had some over heating issues on my md5a and i took off the thermostat housing for the first time. Definitely found the problem there, as there was so much build up inside there's no way water was getting through the chamber. Crazy thing because it pumps a good amount of water out the exhaust when running. Upon further thought i realized that the thermostat was stuck and there was never any water getting through the cylinder head, it just pumping straight through to the exhaust sleeve. I took off all the piping and used a dremel to clean the thermostat housing, that is until i cut a hole through the back of my thermostat housing. Underneath the hole where the thermostat is on the return side of the head it is completely blocked. My question is how do i unclog the hole and clean the cooling channels without the temptation to use a dremel and possibly ruining my cylinder head?

[Captsteve53]

Hi,

Yes well if you have used the dremel tool you now know never to use again!, only hand tools/scrapers and the likes should be used, I have used a solution of Muriatic Acid and water (5 parts water to one part acid)(always add the acid to the water!!) and flush try to let sit for an hour them flush again with fresh water-careful not to spill all over the engine, this cleans the galleries out quite well but might have to do several times followed by a good flush,

Really the cylinder head should come off(yes i know that sucks!), in future there's a product called "Salt Away"which is used by the out board boating community to flush there engines, it not only cleans out the salt in the system but actually helps in prevention of further build ups if done regularly,

Please do not be tempted to run with out a thermo stat as they do an important job(if they didn't need them trust me they would save $20 and not install them) it should be replaced or at least tested in a pot of water heated on the stove- it should start to open @60c and be fully open @90c,

What do you plan to do about the hole?

Cheers Steve

[Don C L]

There are some threads here on this I think if you do a search. I saw a friend with an MD7A go through this. We ended up taking the engine out and had a mechanic friend pretty much rebuild the whole thing. Now he runs CLR through it once in a while and so far so good.

[cborden689]

I have purchased a new thermostat and housing. I have heard of a product called rydlime? Anyone ever use this? As far as muratic acid goes, where can i purchase it?

[gjordan]

Muriatic acid is for sale in most hardware stores but if you cant find it, call swimming pool supply stores. If you ever run without the thermostat you may have to plug one passage in the thermostat housing. The MD6 and MD7 are like that and probably the MD5. I dont remember the details, but running without the thermostat and not plugging the passage makes the engine run hotter. Maybe one of the other owners can tell if the 5 is the same way? _____Grant.

[Captsteve53]

Grant, You have it correct, there's numerous people that dont understand that many or at least 90% of thermostats are what we called double acting-that is when open (hot running around 85-90 c) they actually close off one opening in the block thus forcing the water through the block and the heat exchanger, whereas when cold the water only runs through the block(this is on fresh water heat exchanged cooled engines) but these small sea water cooled engines have the same operational system where as when cold the water just exits through the exhaust (or a proportion of it.)allowing the block to warm up

I have been involved with numerous engines where the owner couldn't under stand why the engine some times ran hotter with the thermostat removed, I have always told people if engine manufacturers could do do with out them they would!- As long as the "other " port is blocked off then yes it will run cold(probably to cold!)