Over the winter of 2020-21, I did valve jobs on both of my 427 engines, then installed aftermarket oil coolers and bypassed the originals. Next, I put new diaphragms in the OEM fuel pumps, and for the first time since we bought the boat in 2011, our 42 DC would jump up on plane and scoot. But then a month ago the starboard engine got warmer than usual ~185°. Dropping the RPM didn't bring the temp down, so I shut it down and ran on the port side back to the marina.

Next day, I found that the coolant level was low. I figured maybe I just hadn't burped it enough back in the spring. So I topped it up and went for a spin. Everything seemed fine.

A week later, the starboard engine once again got warmer than usual. Same pattern as before--a gallon of coolant went somewhere. But it wasn't in the bilge.

Things got busy, so I didn't take the boat out for a few weeks. Until yesterday. We hit the water and within 3 minutes at ~1,000rpm the temp took off again.

Today I popped the radiator cap and started filling...and filling...and filling. I'd put in a gallon of antifreeze, then go fill the container with water and pour it in the expansion tank. It'd almost go to the top, then I'd go fill the container with more water. But when I came back, the fluid level in the expansion tank was very low. This process repeated several times before I decided there's no way this thing has that big of a cooling system.

I started thinking all sorts of dark thoughts--my new head gaskets leak, by block or head(s) cracked. I checked the oil level and found it was perfect. So the coolant wasn't going into the pan. And that's when I noticed liquid dripping from the exhaust manifold studs (outboard, natch).

So I started pulling the exhaust manifold and discovered where all of those gallons of coolant were going: into the exhaust side of the log! Since the bend at the top of the riser is higher than the cylinder head, I figured I better pull the spark plugs. Coolant gushed out from 2 of the 4 spark plug holes on that side. I hit the starter, and jets of coolant sprayed out of 3 of the spark plug holes on that side.

After removing the log, I shone a flashlight inside the exhaust tube. I didn't see anything out of place at first, but then something caught my eye on the far side (the front end of the log). I pulled the front plate off the log and found a large perforation in the cast iron you can see below. As I was pouring gallon after gallon of antifreeze in the top, it was filling the manifold and riser, then flowing through the exhaust valves into the cylinders.

If anybody has any spare exhaust log front plates they can spare, I'm interested. I could weld the hole, but I'm pretty sure that wouldn't last long.


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I have a pair of oil coolers

Let's keep in touch on the risers. I made a set for the Cummins 6BTA Diamonds in my Roamer 46, so I've got a source for water-jet cutting services, though I'd have to make four CAD files for the showerhead endcaps and antifreeze-cooled section end flanges.

On the oil coolers, earlier this year I just decided to bypass the OEM engine oil coolers entirely. I had a set of 3" OD copper oil coolers leftover from the Roamer, so I used those on the Commander. They work great.  3" is overkill, but even 2" coolers will do and they're only ~$100 brand new.

John Mario said:

It would be great if you could design and fabricate these - I would be a willing beta tester :).  Availability of oil coolers, manifolds and risers are the primary factors separating 427s from staying in boats vs ending up in the scrap yards and having a low-cost alternative for risers is a step in the right direction.

I installed the replacement exhaust log end cap and took the boat out for a lunch run with the missus. The 427 Fords sure sound good when those secondaries kick in.

Your Weber grill the best on on the market. I have on for the boat and the bigger one at the house. Thought you had C series on your 46. Have been dying  to ask what going on with the Roamer?????

Thanks, Byron! Yeah, that Weber grill is awesome. It doesn't go with the Commander 42 when she sells though!!!

I do have 6CTAs on my Roamer. Unfortunately, some...outside evil forces have affected my ability to focus on the Roamer. The lawsuits should conclude later this year, after which I hope to wrap it up pretty quickly.

Awesome video - the sound of those 427s coming to life makes the hair on the back of my neck stand up! I hope to run mine at those speeds next year. I’m fighting a cooling issue on my stbd 427 that doesn’t allow me to run it higher than 2500 without exceeding 185F. 

What temps are you running at various speeds?

Thanks John!

The 42 Commanders have two basic speeds: ~1800rpm max hull speed cruise and 3,600 for cruising on plane (w/no trim tabs installed). They'll hit 165~170° @3600 but drop to ~150° at anything less than 2500.

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