...or... "Chowderhead Makes Mayonnaise"

Chowderhead is a 1965 38' SF and she was repowered years ago with tiny little DD 4-53 Naturals.

Ginger, my port engine blew a hose clamp on the lower coolant hose last season and ran dry until the paint on the exhaust manifold started to smoke.  I was in the process of getting my gauges sorted at the time and the smoke was the first (and last) indication.

I changed the oil a couple of times, fixed the coolant hose, new exhaust manifold tips, refilled with FleetGuard and distilled water and she ran like a champ the rest of the season.

Blackstone Labs said they detected elevated levels of coolant in the oil on this year's annual oil report and suggested keeping a close eye so I knew something was up.

Fast forward to shake down day when steam started to blow out the port exhaust at 1000 RPM.  Limped back to the dock on the other engine and found water on the dipstick and mayo under the valve cover.

There are those who suggest it might just be an oil cooler failure but that would be oil in the water, not water in the oil as I understand it.

My DD mechanic won't be part of anything less than a $10K overhaul of a 40 year old, too-small-for-the-boat engine and that doesn't seem to agree with the $200 I have available for this project :)

Necessity being the mother of invention and all, I'm a software engineer who's becoming a diesel mechanic. My plan is to read the manual very carefully, buy a set of head gaskets for $80 and see what I can break.  Worst case; I'll still have a broken engine, best; I'll save it.

Calling on the power of the forum for tips and advice.



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Ely, If you are lucky it may be an injector copper leaking. Injector coppers are pressed into the cylinder head and are in direct contact with coolant. If the copper is cracked it could leak coolant into the oil and the cylinder causing coolant in the oil and burning coolant causing exhaust smoke. It may be a cracked head also, either way the head has to come off. 


Before doing anything, I would suggest to take the air box covers off and see if you can see any coolant in the air box. It would also help if you pressurized the coolant system to encourage the leak when you do this. Just pulling the head and throwing in a new head gasket kit is a sure way to make you $80.00 poorer.

If the leak seems to be coming from one of the cylinders specifically, bar the engine over so that the piston is all the way down and see if if it is the only leak. Putting a bore scope through the liner intake ports is a good way to see what the cylinder head looks like inside. When using the bore scope, also be alert for any leaks in the side of the liner. They do sometimes crack.

Detroits use what is referred to as a burner tube that surrounds the injector. These usually don't go bad. Usually the only problem with them is that if you pull one loose from trying to get a stuck injector out is the main source of trouble. Pressurizing the cooling system with the valve cover off will tell you if this is the source. In an overheat situation, usually the heads crack before a burner tube lets go.

The 53 series are wet liner engines and it is quite common to damage the coolant sealing O-rings on the liners from an engine overheat.

Could also be a head gasket but i'm betting on the liner O-rings.

Be careful that you don't get a hydraulic lock from the coolant leak. Don't need a bent rod added to your problems. Bar the engine over by hand until you locate the source of the coolant leak.

If your problem actually is the liner O-rings, they are not that expensive. You will need the head off to pull the liners anyway and that is why I recommend to find out what the actual problem is before you start disturbing things and muddy the water.

Liners are usually easy to pull. It would be a good idea to have the head checked for cracks and leaks if you do eventually pull it but be prepared for a $2000 expense, for a new head with injectors.

Good Luck with your new adventure in boating.

One other thing I forgot to mention is that the exhaust manifold endcaps have gaskets that like to develop leaks. A leak there will put coolant in the crankcase while setting.

Before you do anything, pressure check the exhaust manifold by isolating it and check for leak down.

This will fit your budget if this is the leak.
Don't know why I didn't say start there.

2 stroke Detroit’s are notorious for cracked heads when they suffer a severe overheat. I would pull the heads and have them floroscoped. 

Thank you for the great replies guys.  I had to spend this weekend finishing the head refurbish to make her ready for my daughter to live aboard while she's home for the Summer.  Nice life, eh?

Ronald, you might be onto something since I had work done to both endcaps last year and had to remove and replace them.  I'll start there.  Thank you for your super-detailed and super-helpful response.  I knew I'd find good support on this forum.

Will keep this thread updated.


Spent some quality time with a pressure tester yesterday.  Initially I heard some hissing coming from the exhaust manifold end cap so I got excited and pulled that off to inspect.  I didn't find a smoking gun when I looked at the gasket but I had a spare piece of star board and a big square of rubber gasket material so it was arts & crafts time.  I traced the old gasket onto both, cut and drilled, fit it tightly with some shorter bolts and pressurized again.

Sadly I can now hear hissing near the #2 (counting back from the heat exchanger) cylinder. No bubbling around the injectors so I'm not suspecting burner tubes yet.

I'm not sure how to tell definitively between the liner O rings which I hope it's not or the head gasketing without pulling the head.

Look at all the nastiness in here.  Coolant and mayo everywhere.

Hoped you were going to luck out.

Next step is to remove the air box covers on the side of the block. They will be on the opposite side as the blower.

Take these off and you will be able have direct visual and audio access to the liner ports.

A bad liner o-ring will leak between the liner and the block.

Bad head gasket will have air coming out of the liner ports while doing a leak test.

It is very likely that you have a blown head gasket but it is important at this point to make sure before you pull the head.

If you pull the head, you really should have it magnafluxed, crack tested.

Manafluxing the head is cheap but the results might not be what you want to hear. Just warning you.

Hi Ronald.

I opened the air box and it was oily but free of water in there and quiet under pressure.

Next job was to remove the head and there I found the smoking gun. One of the harder plastic rings in the front left corner was just a pile of melted plastic and you'll see the obvious mangled larger white ring and its accomplice, the split smaller white ring.

Chambers counting from the fron (right side in the pic)

t; #1 bone dry, #2 bird bath, #3 kiddie pool, #4 Olympic high dive pool.

The cylinders look fantastic for an engine that has been in service for 40 years, cam looks good, followers shiny and happy even if a little mayonnaise covered.

Valves look happy.  

Thought about sending the head out to check for cracks but that would bean removing the fuel pipes & injector racks which I'd like to avoid disturbing if I can.

I have 20 ziploc's with bolts and parts all labeled and ready for reassembly.  Ordered the new gaskets from Dieselpro for $40.  If they get here before Tuesday I'll be able to get to work reassembling.

Top is front here.

Thank you for all of your good advice.  Honestly just having someone else interested in this project/problem has helped me feel like I'm not doing it alone.



I'm a little concerned with the looks of #2 piston. It might be just the picture but it looks to me like there is substantial erosion, particularly the piston point in the center of the piston. Might just be coolant deposits also.

Ely, unless budget is really an issue, you already have the head off, you’d really be silly not to send it off to a professional machine shop at this point and have it gone through. That’s so illogical I had to say something. It’s only like $800 unless you need a new head, which you’d rather know now than after you put it back together. Also the cam timing is easy on these, it’s the fuel racks and fuel timing that’s a b#tch. Put new pistons and liners in, put it back together and then call a Detroit specialist to do the final setup. 

FWIW I recently went through the same thing. Working alarm bells are a must. Also you do need new pistons judging from the one you can see in the picture. If the fuel bowls on top are that bad I can’t imagine the rings are perfect.

Hi Chris.

I'm going to have to take the silly route here as I'm $800 short of that $800 X-Ray.  Thanks for the engine porn. They're looking really nice.

Side note: I'm using dieselpro.com for my parts.  Do you folks have any other sources?  I'd be particularly interested in replacing this disaster in waiting.  It's the freshwater outlet of my heat exchanger.  

The rust came from a bad gasket on the saltwater outlet just above it that had been neglected for long enough for this to happen.

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