3" heat exchanger

[Jeff Kaplan]

I have the standard 2" heat exchanger on my 1986  M25. I experienced over heating late in our season. It has been boiled out at a radiator shop  a few times already.  I know many have upgraded  to the 3". What, other than getting new clamps to hold it on the bracket, do I need to get for the upgrade? The boat is covered for the winter, but I want to get everything needed soon so if there is some mild weather, I can start the project.  I saw some aftermarket exchangers in the high $300- range, that come from reputable mfg's., Mr. Cool is one. Do I need bigger hose and fittings or will the ones from the 2" one work? Thanks for the replys

[KWKloeber]

Jeff,

See Reality Check's blog which goes thru it in detail.

You need to reshape the bracket to fit the 3" (some leave it as is.) 
I had a pc of iron pipe that was just about the right OD and used it to hammer the old bracket into a larger OD. 

Use the ABA/AWAB style clamps, as regular worm drive can break if they are tight when the Hx expands.  In fact I have changed every clamp to the better ones -- there's no comparison.  The hose sizes are the same.  The new Hx made it hard to get at the dipstick (actually to pull it out past the larger diameter.)  I simply put a quarter-size dimple (ball pein hammer) in the Hx above the dipstick and it passes right past it now.  Pic attached.  I'll send a quote on a Hx, you just need to decide whether you want the 90 degree or 45 degree inlet -- see RC's blog.

Ken

[Stu Jackson]

Pretty much nothing.  I don't even need that dimple, I just use an extender bar on a socket to loosen the transmission dip stick.  Goes straight through.  I originally bent the first support bracket, but when it broke, I didn't bother bending the new one.

http://c34.org/bbs/index.php/topic,6920.0.html

[KWKloeber]

Interesting, Stu.  Possibly there's a difference in where the larger  Hx has to sit on the 30.  Due to the low "overhead" in the 30 engine box, the riser is very tight to the
Hx, so my reformed  bracket may be bent a little closer to the tranny, so the stick woundn't pass. Especially if you didn't reform the radius and so the tube sits even a little higher.

-ken

[Stu Jackson]

Could be, Ken.  Could also be that because of the arrangement of our exhaust riser, there is simply different geometry involved on our boats.  As Ron Hill always says: "Make sure you do the dollar bill test between the riser and the HX."  I discussed this in detail in my recent tech note.

http://c34.org/muffler-exhaust-riser-replacement-2015/

[Ron Hill]

Jeff : There was a recent post By Phil S. #789 on his making a new 3" HX bracket with a notch so it was easy to pull up the xmission dip stick.

just make sure you do the "Dollar Bill Test" to make sure that there is clearance between the HX and the exhaust riser insulation - or you'll be popping the hose clamps that hold the HX in its saddle.

a thought