Here are some details of yesterday's research
Took the heat exchanger/manifold (HE) and elbow to the Yanmar
dealer. He said many have tried to weld up those corroded housings around the cap and few have been happy for long. He looked at the mixing elbow and said it was the cleanest 20-year 2900 hour elbow he had ever seen. BUT, that hole in the exhaust gas tube is a real problem. It allows sea water
to spatter back in the exhaust manifold. If the engine
stops with an exhaust valve open it is possible for salty gas or even salt
spray to get pulled back into a cylinder as it cools and makes a lower pressure IF the seawater comes back to the exchanger from the hole - I do not see how that could happen but it would not be good if it did.
New 4JH2E exhaust manifold and heat exchanger body $1,250 which DOES NOT include any fittings - sort of an engine
short block (end caps, O-rings, nuts, bolts, radiator cap fitting, petcock for draining housing, EXCHANGER BUNDLE for the coolant
are not included)
That means I have to get the bundle out of the current
exchanger to either repair
the exchanger housing via welding or to install the old bundle in a new housing. He said bangthe old bundle hard with a rubber mallet.
A new heat exchanger bundle is $850
OR - $2,100 for a complete cooling
system including bundle, housing, all fittings and mounting hardware
He also thought it pretty important to replace the mixing elbow to keep the sea water from getting back to the new or repaired heat exchanger. The Type U elbow I have is a Yanmar part and is used to 1) get the exhaust and water flow 12" higher than a standard elbow 2) decrease the downward angle of the exhaust hose to allow it to connect to a waterlift muffler
close to it's level.
New mixing elbow $850
WHY did this happen?
1) The mixing elbow damage is unavoidable because the hot exhaust gases have to make a 75 degree turn 6" after they leave the manifold. The inner tube of the elbow (contains and re-directs the gas) is very thin material and erodes over time. The Yanmar guy say few boaters experience this problem because the elbow clogs up with other stuff before the erosion occurs. It seems to me that a LOT of hot rods and diesel
trucks have 90 degree bends just inches from the exhaust valve and those tubes do no suffer similar erosion. Or, do they after 120,000 miles or 2900 hours of usage?
2) The corrosion
on the front of the HE around the O-ring is due to dissimilar material (aluminum exchanger, bronze end cap, steel
bolts) and is pretty hard to prevent. He says that removal
of the cap, bolts, and bundle every few years and a thorough cleaning
with fresh water will slow the problem but it is still dissimilar metal.
Only four to five days to get a whole new system or $13,000 for an entire new engine! (but no elbow)
I took the exchanger and mixing elbow to the recommended welder who was friendly and talkative - he told me:
- Yanmar casting quality control is very poor
- Some castings are near perfect and very easy to work
with and weld up nicely
- Some castings are so full of impurities that nothing will weld to it
- Some castings are poor and look like the weld will work
but after a while it becomes apparent the weld will be low quality
I need to get the bundle out of the housing and then have it gently bead blasted. He estimated $50 to $100 for the beading. Then he will know within 30 seconds if the material in the casting is worth working on. His setup charge to do the first 30-second weld is about $50.
If the weld seems OK he figured about $300 - $400 for the welding and machining to give a flat face and an O-ring groove.
He has done quite a few and says that if he feels good about the welding after a couple minutes they always work out OK.
At that point I would have $500 invested in a 20-year old heat exchanger that might fail in some other way. Or, buy a new one for about $1,125.
Seems like a new one is a good idea.