I rebuilt my 4-108 about 3 seasons ago and all has been well up till recently (apart from a little white smoke - but that's another story and it's been there and unchanged since the rebuild). I've done about 700 hours since the rebuild
First recent problem was the fresh water
pump, which started leaking on a 4 day passage
. Started as fine mist then progressed to all-out spay. Replaced the water
pump a week back. All seems OK with that and this may not be related at all to the main problem.
However, while I was installing the new pump I noticed a small drip under the elbow
hose that goes from the engine head
to the heat exchanger
(leaking my green 50:50 fresh water/anti-freeze mix)......but when I removed the hose to clean it and gunk it back up I found pretty extensive corrosion
on the alloy hose fitting on the heat exchanger
. No corrosion
on the steel
hose fitting on the head
To make sure I did a thorough job of the rebuild
I replaced the original heat exchanger with new when I did the rebuild - it too was extensively corroded! I'm shocked that the new one is corroding as it cost a small fortune to get one down here in NZ ($3,000 odd) so I need to find out why.
Only thing I have changed of any significance that I can think of is the hot water cylinder which tees off the fresh water side of the cooling
system. The previous hot water cylinder lasted 25 years which I thought was OK.
Maybe the original heat exchanger corroded for the same reason and I have just bought myself more time?
As many of you know there is no anode in the heat exchanger and no place for one I can see. There are no anodes on the engine
either as far as I know. The engine is a 1986 4-108 NEW model.
I think it must be electrolytic corrosion (a "battery" effect that requires a current
and water). What do you think?
Anyone got any ideas?