Now we have something to go on and can form some hypotheses.
I still think that the similar heating
problem has a similar ultimate cause, but now we have an idea of a main part of the system, and how it might interact with other parts
First, I would discount (for now at least) cracks in any part of the HE/manifold.
Second, the seal of the boots on each end of the HE is what keeps the fresh water and salt
water from mixing; they must be tight, the bundle must be properly positioned, and the seal between the H/E bundle and the rubber (the small hose clamp) must be perfect.
While we're on the H/E seal subject, a leak there (between the F/W/R/W side) could result in higher-than-normal F/w side pressure, but it wouldn't explain air bubbles, unless you had an issue on the vacuum side of the R/W pump...
So, presuming that on a new engine there are no sealing or mechanical problems, after you ensure that there are no leakage issues within the HE/manifold, a good place to turn would be preexisting conditions.
And to me, that would mean an oversized prop (or one that appears to the engine to be oversized) or exhaust restrictions.
Regarding the prop, it could actually be
oversized, or friction from an improper alignment or worn components could be contributing enough friction to overload the engine.
The potential for exhaust restrictions doesn't stop at the exhaust elbow
If you have a water-lift exhaust, an excessively long, excessively high or undersized run of exhaust hose could cause a portion of the exhaust to feed back through an imperfect raw water heat exchanger seal (incidentally the same general path it would take from a cracked manifold), which could result in both air (actually exhaust) bubbles and higher pressure in the HE.
Another source of restriction is an excess of RW flow into the water lift
which will displace the area available for exhaust and could contribute to overheating. The fact that you have a new, free flowing HE bundle would tend to support this.
So a kinda summary hypothesis could be that there is no individual
cause of your problem (though there could be), but that it is the combination of several smaller contributing factors that are the ultimate source of the overheating.
We had the same problem with a TAMD41 that we finally resolved with 4 steps down on our initial propset selection (A4 from A8, Volvo
doesn't rate it's Duoprops with numbers for pitch
and diameter) and the addition of a tee off for a 5/8'" bleed-off (or pisser) at the point where raw water was injected into the exhaust elbow
. The pisser exits on the starboard side; an added benefit is the visible evidence that the RW pump is working, as well as the current
state of the impeller...
Took us about six months to sort it out, so before you start pulling a new engine apart, have a go at trouble shooting and minor (relatively) modifications. The option to replace the head gasket
is always open...