CN4-33 EXHAUST MANIFOLD CAP

[pctekky22]

WE HAVE A 1975 MORGAN OUT ISLAND KETCH WITH THE CHRYSLER NISSAN CN4-33 DIESEL ENGINE. AFTER THE ENGINE HAS BEEN RUNNING FOR AWHILE, COOLANT STARTS TO LEAK OUT THE CAP. DOES ANYONE KNOW WHERE I CAN GET A CAP THAT FITS THIS MANIFOLD PROPERLY. WE THINK THE CAP WE ARE USING IS NOT SEEDING PROPERLY. ANY ADVICE I CAN GET WILL BE GREATLY APPRECIATED.

[plenzen]

As far as I remember those was a standard type automotive rad cap, although I cannot remember how many lbs. they were but I think they were 6 or 8. (Tom Young may be abel to advise what his is) The castings that the manifolds were made from were really not all that good even new but, if the machined portion at the bottom of the filler neck is smooth and not corroded and pitted then I would be suspicious of perhaps a head gasket problem and look into that possibility if a fresh cap does not solve the problem. Is there a lot of pressure in the system when this happens, or has the engine oil turned milky? If the pressure is released when this happens and you can see inside the tiny tank at the end of the manifold with a flashlight and the collant has lots of bubbles or foam in it that might tell you what is going on.

Paul

[asavage]

Heather, we only have a couple of members with the CN version of the SD. Our most active member is Tom Young in Maine, who is retrofitting a 720 SD to replace his CN. Hopefully, he will pop up and have a suggestion. Read about his project in this thread.

Is there any chance you can snap a picture and post it or email it to me?

[Tom Young]

I sent you a response through your pm, but I'll post it here too.

First, is the engine cooling correctly? Does the blow off stop after an amount of coolant goes out the overflow?


As mentioned, the seat for the radiator cap may be corroded. Some cleaning and maybe some even abrasive work to smooth it out may help that.

I believe mine is a standard radiator cap but I can't read the specifics on it.

One of the reasons this may be a problem is the high volume of coolant in the CN4-33 system. With the exhaust manifold reservoir, the heat exchanger for cooling, and a water heater, if you have one in the loop, my engine holds just over 3 gallons of antifreeze. I think that volume must expand quite a bit as it reaches operating temperature. Mine is fitted with an expansion tank. Still, it seemed to blow off some coolant until it reached a volume that could expand properly. This volume was well below the filler neck of the manifold, but the cooling system worked correctly.

Also, due to the angle of the engines installation on a boat, the coolant level should be lower at the cap (several inches at least) or there will be little room for expansion.


So check the expansion tank, it's line for plugging, maybe add one if there isn't one. I may look into fitting a larger expansion tank if I have the same problem with my new CN-SD22.

I'll be running the engine up to temperature in the next week when the boat goes in the water and find out how if I have the same problem.

[Tom Young]

I'm sure my problem with losing coolant was the corrosion at the seat in the manifold coolant neck Heather.

I scraped more rust out of the area with a flat screwdriver blade. Then I used a socket that fit loosely with abrasive paper wrapped around it. Turning this in the neck honed it down smooth and flat. I kept a bottle on the overflow tube to test and found no coolant after runnning up to temperature on the water.

This close up shows the manifold on the CN4-33 and coolant plumbing. The line off the Tee between the manifold and the thermostat housing runs to my expansion tank above in a cockpit locker. That's working correctly now. Between the 5 feet of hose and the tank, quite a bit of coolant expands out of the system.

I've noticed another CN4-33 does not have the small taps and hose between the manifold and the face of the thermostat housing. This was plugged with build up on my old set up (I found when I took it apart).

So clean and sand that seat, and use a standard radiator cap, that will fix it. And I almost forgot. I used some water pump grease (Lubriplate) on the seating area to keep corrosion down.