I'd try the acid flush first. A common maintenance measure on Atomic 4s, most of which are raw water cooled. If the passages are not completely blocked, it may help enough to eliminate the overheating problem. I did it several times on my previous boat which had a raw water cooled Universal 5411. I used oxalic acid from the hardware store.
07-18-2013 02:25 AM
Remove Exhaust Manifold, or Rydlyme flush?
As mentioned in a separate thread, I'm having some mild overheating problems with my 1981 Yanmar 2QM15 (raw water cooled). Web research suggests that the water passages are likely occluded.
Some people recommend physical removal of the exhaust manifold and elbow for cleaning/tanking. Other people recommend flushing with Rydlyme or equivalent.
I'm a little hesitant to remove the manifold if I don't have to. 30 plus year old fasteners and parts have a way of giving out, and some of these items (like the manifold itself) are no longer available. On the other hand, if the exhaust manifold passages are as clogged as some people suggest, the Rydlyme might not be adequate.
Anybody been through this before? Recommendations?