2" to 3" Heat Exchanger on Universal M25

[Hugh17]

I want to install a 3" Heat Exchanger on my Universal M25 where I currently have a 2" Heat Exchanger. The problem is that the mounting bracket for the 2" HX is too high for the 3" HX to fit under the exhaust fitting, and I cannot shift the 3" HX far enough away from the exhaust fitting to work.

Has anyone fabricated or know if an after marker Heat Exchanger bracket is available for mounting a 3" HX on a Universal M25 engine? Pictured below is the mounting bracket for a 3" HX off a M25XP on the left and the mounting bracket a 2" HX off my M25 on the right. Also pictured is the back of the engine where the 2" mounting bracket attaches using 2 bolts from the bellhousing.

The 2" mounting bracket bolts to the bell housing on the M25 through the vertical bends of the bracket. The 3" mounting bracket attaches with 2 bolts into the top of the bellhousing. My M25 does not have bolt holes in the bellhousing.

I envision the remedy for this problem to be a modified mounting bracket with mounting bolts the same as the bracket for the 2" HX but to extend back and lower in order to accommodate the 3" HX. I've search the previous posts about this and can't find any specific information about a modified mounting bracket.

I appreciate the help in advance.

[Stu Jackson]

James,

The bracket can be bent down enough to clear.  That's what I did.

[KWKloeber]

Hugh

The flat 3" bracket is for (one of) the M-25XP bell housings (there were different bell housings used.) 
Wb or Universal never fabbed a 3" bracket for the M25. 

It's eazy peazy -- simply open up the 2" bracket to fit the 3" Hx.  I happened to have a 2' length of iron pipe that was 3" OD and with my trusty, heavy, ball peen hammer just opened up the radius enough.

You can also bend the bracket lower so the HX fits under the riser (see pix.) 

The next problem is getting the tranny dipstick out with the 3" Hx in the way.  I put up with that for about a day, then (w/ a smaller ball peen hammer) put a small (nickel size?) "ping" in the Hx, right above the dipstick, positioned so there's just enough room to slide it up and out at an angle.  It doesn't affect the HUGE excess cooling capacity of the 3" Hx and works great.

Some (and Noah) relocate the Hx off-engine - he can chime in on that.

Another had fabbed a longer bracket to uncover the dipstick, but that was during an exhaust remake when installing the water-cooled riser -- which I am sure you don't want to get into.

-ken

[WTunnessen]

You might consider relocating the HX altogether.  I plan to remount mine further aft to improve access to the transmission fluid dip stick.  Also gets the HX away from the exhaust pipe. There were some post earlier about doing this. I have the flat type of mount and plan to reuse by basically bolting somewhere below the aft berth.  Not sure if I will need some sort of extension.

[Hugh17]

James,

The bracket can be bent down enough to clear.  That's what I did.

Stu,

Thanks much. That sounds simple enough. I bent the curve of the 2" bracket to fit the 3" HX and remounted it on the motor. When I tried to install the 3" HX I couldn't get it to clear the exhaust fitting. It was difficult to work over the back of the motor trying to hold the 3" HX on the bracket when it wouldn't fit, so I really couldn't tell how much adjustment was needed for clearance.

Since I had both the old 2" HX and 3" HX cleaned, pressure tested, painted, and ready for installation I decided to just install the 2" HX so I could get the project finished.

If you have a picture of your modification or even the 3" HX installed please post here at some point. That will be a good reference as to how much bend is needed.

Thanks again,

[Hugh17]

You might consider relocating the HX altogether.  I plan to remount mine further aft to improve access to the transmission fluid dip stick.  Also gets the HX away from the exhaust pipe. There were some post earlier about doing this. I have the flat type of mount and plan to reuse by basically bolting somewhere below the aft berth.  Not sure if I will need some sort of extension.

If you make the modification please post some pictures. I'm going to live with the 2" HX until the next time it needs to be removed and flushed. By then I hope to know what needs to be done to install the 3" HX and leave the transmission dip stick available for checking. '

Thanks,

[Hugh17]

Hugh

The flat 3" bracket is for (one of) the M-25XP bell housings (there were different bell housings used.) 
Wb or Universal never fabbed a 3" bracket for the M25. 

It's eazy peazy -- simply open up the 2" bracket to fit the 3" Hx.  I happened to have a 2' length of iron pipe that was 3" OD and with my trusty, heavy, ball peen hammer just opened up the radius enough.

You can also bend the bracket lower so the HX fits under the riser (see pix.) 

The next problem is getting the tranny dipstick out with the 3" Hx in the way.  I put up with that for about a day, then (w/ a smaller ball peen hammer) put a small (nickel size?) "ping" in the Hx, right above the dipstick, positioned so there's just enough room to slide it up and out at an angle.  It doesn't affect the HUGE excess cooling capacity of the 3" Hx and works great.

Some (and Noah) relocate the Hx off-engine - he can chime in on that.

Another had fabbed a longer bracket to uncover the dipstick, but that was during an exhaust remake when installing the water-cooled riser -- which I am sure you don't want to get into.

-ken

Thanks Ken,

With my luck the "ping" in the HX would be a death blow. I'm leaning toward making a new bracket based on the mounting bolts required by the M25. I'd like to extend the bracket back and down enough to clear the exhaust fitting and leave a gap for checking the transmission fluid. I don't know if this is possible but I will look at when I need to remove and clean the 2" HX the next time. At least I'll be a little more prepared and realize that I have to do more than just hope the 3" HX will fit.

If (or) when I get to this I'll post pictures, etc.

Thanks,

[Jon W]

Something to consider is mounting the 3" HX to the underside of the Aft berth using the bracket in your right photo. First photo below is underside of aft berth looking forward showing installed bracket with my old HX (had to replace). Second photo is my new HX same bracket from above engine looking aft.

[KWKloeber]

http://c34.org/bbs/index.php/topic,9512.msg71759.html#msg71759

Above seems a whole lot easier and ends up better access than permutating in it order to keep it 'on-engine.'

Do you 34s have to access the dipstick by leaning over the engine and dangling your whatnots out wherever?  I thought we had it tight.

[Stu Jackson]

James,

Here's my bracket.  I'm guessing it's an old 2 bracket.  This photo is from 2015 when I replaced my muffler and exhaust riser.

The remote mounting makes a LOT of sense.

[Ron Hill]

James : If you elect to expand the old bracket make sure that when the 3" HX is mounted that you have clearance between the top of the HX and the underside of the exhaust riser!!  I wrote a Mainsheet tech note article on the "Dollar Bill " test (being able to slide a Dollar Bill between the two) Even if you have to remove some of the underside riser insolation.

Actually the "Under the aft Berth" is a great idea as you can more easily get at the Xmission dip stick!!! 

A few thoughts

[Hugh17]

James : If you elect to expand the old bracket make sure that when the 3" HX is mounted that you have clearance between the top of the HX and the underside of the exhaust riser!!  I wrote a Mainsheet tech note article on the "Dollar Bill " test (being able to slide a Dollar Bill between the two) Even if you have to remove some of the underside riser insolation.

Actually the "Under the aft Berth" is a great idea as you can more easily get at the Xmission dip stick!!! 

A few thoughts

Ron,

Of all the ideas offered I like mounting the HX on the underside of the aft berth. It appears that the access to change the zinc is pretty easy and also the access to check the transmission fluid is open.

I am also thinking of running my water heater hoses off the coolant hoses before they connect to the HX, so all that plumbing work could be done easier with the HX located away from the engine.

Thanks,

[Hugh17]

Something to consider is mounting the 3" HX to the underside of the Aft berth using the bracket in your right photo. First photo below is underside of aft berth looking forward showing installed bracket with my old HX (had to replace). Second photo is my new HX same bracket from above engine looking aft.

Jon,

You definitely have my vote for the best idea so far. As I mentioned in another reply to Ron, I like this option because it solves all the problems:
1) Access to change the zinc is easy
2) Access to check the oil in the transmission is unobstructed
3) Doesn't interfere with the exhaust flange
4) Allow better access for possibly routing the water heater hoses to T off the coolant hoses near the HX

I'm going to run with my old 2" HX since it's cleaned out and already installed. But in a year or so when it's time to clean it out again, I will already know how I want to install the 3" HX and water heater hoses.

Thanks much!!

[KWKloeber]

[edited]

If your water heater hoses:
   a. Run in a separate loop from the thermostat/coolant pump, don't change that.
   b. Run in series with the 2" Hx, then change that
(IWIIWMB&Hx)
It took CTY like 4000 [C-30] mk-I installs before figuring out the correct plumbing and how virtually every other marine engine (blow and stink) run the water heater.

[Hugh17]

[edited]

If your water heater hoses:
   a. Run in a separate loop from the thermostat/coolant pump, don't change that.
   b. Run in series with the 2" Hx, then change that
(IWIIWMB&Hx)
It took CTY like 4000 [C-30] mk-I installs before figuring out the correct plumbing and how virtually every other marine engine (blow and stink) run the water heater.

When I had the M25 installed after buying the boat in 2014, we had to disconnect the water heater hoses. They were leaking so replacing them and connecting to the M25 wasn't necessary. I replaced the water heater earlier his year and hope to connect it to the engine coolant system when I finalize th HX swap to the larger size.

I saw another post on this forum that discussed connecting the water heater hoses off the HX instead of on the engine off the thermostat housing. That is my intention.