Help for my Diesel Slipmate?

[roadnsky]

Calling on the fleet for help here...

Today my slipmate approached me with an issue he is having.
First, some preamble:
36' Islander with original factory Volkswagen Diesel
Engine was rebuilt last year by current owner
FWC system that owner feels is original to the boat
FWC also has a Hot Water Heater bypass
Engine appears to run very well
Normal op temp is 190°

Symptoms/Issues:
At RPM's above 1500, the HX overflows coolant.
Below 1500, no overflow. No issues.
When overflowing, there is NO overheating. Gauge shows 190°
No engine or running issues. Just the coolant overflow.

I'll confess here to not paying very much attention to FWC systems.
My excuse is that I'm RWC in a fresh water lake (Lake Mead)

Could it be as simple as he possibly just has the wrong pressure cap on the HX?

So, reaching out to the gang for some advice we can give to my friend.

[zellerj]

I would shoot it with an infrared temperature gun

If gauge is wrong and it is in fact overheating, that would explain the overflowing. If it is not overheating, I don't have an explanation.

[roadnsky]

I asked him if he was certain that it wasn't overheating and he said temps are normal.
AND as soon as he throttles below 1500, the overflow stops.

[nyiftos]

yes, replace radiator pressure cap and retest.

[ndutton]

Did somebody say Islander??

I think your neighbor may have more than one factor working together to produce the symptom. What follows is of course pure speculation but here goes anyway:

• As others have suggested, replace the cap. There's no harm in trying. With a lifetime of FWC he could probably get away with something as high as 14 psi but 4 ~ 7 psi should do fine. We don't want to mask a problem with a big pressure cap.
  
• Trapped air in the system. Scrutinize the relative elevations of system components especially the relationship of the overpressure cap and the water heater. We want the cap to be at the highest point in the system and ideally with all flow headed uphill to it. If that is not the case he'd do himself a huge favor adding a header tank, routing the hoses accordingly and relocating the overflow bottle to the new header tank location. Bleed valves strategically located at any up traps will aid in burping air pockets.

If the second bullet item is true, it suggests to me that something about the system may not be factory original. The engineering staff (chief engineer specifically excluded) were a sharp bunch of guys and fully understood the need and function of header tanks in such an installation so it is unconscionable to me that if the factory installation needed one it would not be there. Islander is where I learned about them.

Other stuff about your neighbor's boat. I suspect is is a very late 70's or early 80's model year. Prior to that the factory diesel option on the Islander 36 was the venerable Perkins 4-108. The Pathfinder (VW) didn't appear until very near the end, something like 1982, well beyond my time there.

edit:
Jerry, take a hard look at the port and starboard cockpit seat risers and knowing how the molding process works, particularly the need for draft (the mold must be larger in the direction of release to be able to remove the finished part) try to figure out how it was done. FYI, the deck was molded as a single piece.

We are talking about the Islander 36 sloop, the Alan Gurney designed racer, right? Not the Bob Perry designed Islander Freeport 36, a cruiser all the way.

[lat 64]

If this is the Rabbit diesel, then I have a little (very) experience with these.
I used to do valve jobs on them and one of the common issues was a warped head from either overheating or just time. It seems the head castings were made in a tall blocky way. They needed long head bolts. The aluminum in the head would sort of shift like putty when it got hot, then when it cooled it would shrink, loosening the bolts. Then the head gasket would fail, seeming to be overheating. A lot of these heads needed quite a bit of resurfacing to get them flat again.
One way to deal with this problem was to keep a regular maintenance schedule to re-torque the head bolts periodically.

Just sayin' could be a blown head gasket

Hi all,
Russ

[Dave Neptune]

Maybe simple

Jerry, if all is well with the engine and head it might be this. I have only seen this twice but here goes. Perhaps the flow of the pump is exceeding the capacity of the lines, fittings and accumulated debris on the down side, so it may not flow as much as the pump any more. I saw this once when a higher capacity pump was added and the other was just from old age and accumulated KRAP in the lines.

Reaching a bit on this one.

Dave Neptune

[roadnsky]

We are talking about the Islander 36 sloop, the Alan Gurney designed racer, right? Not the Bob Perry designed Islander Freeport 36, a cruiser all the way.

Oops! I totally forgot to mention this is the Freeport 36.
I think I recall him saying sometime back it's a circa '82.
(It's a great cruiser!)

Russ-
Yes, it's the Rabbit Diesel.
He tells me he rebuilt it last spring.

Thanks guys for the ideas. I'm gonna print them out to give to him.
I'm trying to get him to just come on the site and discuss. I explained we help diesel folks out here too. We'll see...
I expect I'll see him again today or tomorrow and I plan to go on his boat and look around.
I'll take some pics which should help explain his setup.

Thanks again

[ndutton]

Oops! I totally forgot to mention this is the Freeport 36.

Well then, that changes things. The Freeport 36 (introduced in ~ 1977?) was originally built with the Perkins as well and had the factory header tank due to the water heater elevation I mentioned earlier.

Worthless trivia: Guess who wrote and photographed the original Freeport 36 Owners Manual? (it was done in a rush and wasn't very good)

[roadnsky]

Guess who wrote and photographed the original Freeport 36 Owners Manual?

So... maybe I don't have to take any pictures?

Seriously, I'm hoping I can just get him to sign on to the site here and we can discuss with him directly.

[JOHN COOKSON]

. Perhaps the flow of the pump is exceeding the capacity of the lines, fittings and accumulated debris on the down side, so it may not flow as much as the pump any more. I saw this once when a higher capacity pump was added and the other was just from old age and accumulated KRAP in the lines.Dave Neptune

Sounds like a person.
I vote for marine engine style congestive heart failure.
The escaping coolant is the equivalent of blood backing up in the lungs.

TRUE GRIT

[lat 64]

I surfed a bit and realized the head bolts may be some early torque-to-yield style. This may be a contribution to a rebuild failure. I am only pursuing this line of reasoning because I can. I hope it's really like Dave says, a pump flow issue.

Check for oil leak at gasket too.
A discusion of Vee-Dub rattle wagons is here:

http://www.vwdieselparts.com/forum/viewtopic.php?f=8&t=12029&p=84438&hilit=head+gasket#p84406

Russ

[hanleyclifford]

Jerry, if all is well with the engine and head it might be this. I have only seen this twice but here goes. Perhaps the flow of the pump is exceeding the capacity of the lines, fittings and accumulated debris on the down side, so it may not flow as much as the pump any more. I saw this once when a higher capacity pump was added and the other was just from old age and accumulated KRAP in the lines.

Reaching a bit on this one.

Dave Neptune

Wouldn't be hard to install a 1-15 psi gauge downstream of the pump to test that hypothesis.

[sastanley]

For the record, MMI sells diesel parts so we are still on topic..