Moving a heat exchanger

[wayneR]

The heat exchanger on my Oday 34 was upgraded to a larger size due to overheating problems with the Universal Model 25. That problem was solved but now I can't easily check the transmission fluid since I can't get the dip stick out. (Heat exchanger mounts over the transmission). I'm thinking of moving it to a nearby bulkhead. Except for changing four hoses and fabricating a mount, I don't see any problems.

AM I OVERLOOKING SOMETHING????

Any insight from someone who has done this would be appreciated. wayneR

 

[RichH]

Moving the heat exchanger to any location should not be a problem.
If possible keep the 'runs' of hose as short as possible (and 'supported' if possible if 'long') and use as 'few' elbows and other plumbing fittings as possible' ... this will keep the 'pressure drop' of the fluids to a bare minimum. The more 'elbows' and fittings and the longer 'run' of hose will promote higher 'friction losses' in the fluid lines .... and will retard 'mass transfer' (amount of fluid).

Since you upgraded to a larger surface area Hx you should therefore have 'reserve' capacity to handle a 'lot' of additional 'fluid friction' needed to make such a remote installation, .... so the advice is just 'standard practice'.

 

[kloudie1]

Getting the air out is the only real issue.. the hose runs need to be going level or slightly uphill to the heatex to be able to bleed it. Most important is to not put any form of "upside down P trap" in the hoses where a bubble could be trapped and never bled out. You may also place the heatex lower than the old mount if there is a good way to bleed air at the system high point. Rich's points made about fittings and distances are correct and should be heeded as well.. ..

 

[Stu Jackson]

On the M25, the highest point in the closed (freshwater) system is the thermostat when the HX is located on the bracket at the aft end of the engine. However, since the freshwater section of the HX is completely closed, and cannot be vented, the height should not make a difference. You still will need to "BURP" the system to avoid engine overheating when you replace the HX, fill up the coolant and start the engine. If you know about burping, fine, if not, reply #6 here: http://c34.org/bbs/index.php/topic,4518.0.html

We replaced our old 2" HX with a new 3" model and had the engine bracket bent down a bit to allow clearance. I'd thought about relocating it, as you have, but didn't need to.

I am a proponent of inspection of HX on a regular basis. Reason? Reply #3 here: http://c34.org/bbs/index.php/topic,5736.0.html

You could, as an alternative, use your yearly HX inspection, taking it off and checking it out, as the time to do your transmission fluid change. That way, you needn't relocate it.

You might also get enough wiggle room if you just loosen the hose clamps.

We have never felt a need to "check" the transmission fluid level except when we remove the fluid for a change. Unless you have a leak, it ain't goin' anywhere. This after 13 years with a 1986 boat.

Good luck.

 

[Maine Sail]

This is not just a problem on the older M-25's when upgrading the HX to 3": but the newer M-25 XPB also has issues with the gear box dip tube hitting the HX, had the same problem on a 2005 motor.

By far the easiest solution is to loosen the HX to check the gear box fluid level. With clean fluid it is near impossible to see the level anyway and this level is checked with the dip tube not threaded in but just resting on top. Our Hurth/ZF v-drive is nice it takes exactly 1 quart after a complete draining off the bottom tapping. The whole gear box fluid change takes me all of 4-5 minutes and a $2.50 quart of ATF..

I am a HUGE proponent of annual fluid changes in the HBW series gears used on these motors. I do my own v-drive annually and the v-gear gear is at less risk of metallic shavings damaging the thrust washers. You can suck about 90% out through the top then drain the last 10% into a baking tin covered in oil absorbing pads. It will cost you about $2.50 to do this as it takes a quart.

If you do this the only time you'll need to really check the fluid level is if you notice some in the bilge. Change the fluid, including draining off the bottom tapping completely, and these gear boxes can last for a very, very long time. Oh and NEVER leave it in forward while sailing and if you do a double change is a very, very good idea..

Metallic particles from the clutch plates wind up in the fluid and can kill the clutch plates and thrust bearings when they are splash lubed with AFT containing metallic content.

 

[wayneR]

A follow-up: I did the move and it worked out fine except for one overheating episode. I let it cool, removed the thermostat, filled the block under the thermostat with antifreeze, put things back together - problem solved. These engines need to be "burped" when you drain the antifreeze. Lesson learned. Thanks to everyone who replied. WayneR

 

[Tim R.]

Wayne, you should have a petcock at the top of your engine for burping. No need to remove the Tstat.

I had an M25XP on my previous boat and the HE was mounted on the back of the engine with the factory bracket and 2 hose clamps. I found that although the dipstick is difficult to get to there is enough room to pull it up and lean to one side to remove. You may have to play with side to side position of HE to get this right.

 

[Stu Jackson]

Wayne, glad to hear it went well. I agree with Tim though, 'cuz my link to Burping explained why you don't need to remove the thermostat to burp your engine, ever.