Steamy smoke and high running temperature

[TorMar]

On our 1989 E34 Universal M25XP with 1260 hours on it, we noticed a steamy exhaust and higher running temperatures when cruising at 2300 plus rpm. I did the usual - change raw water pump impeller, clean out raw sea water strainer, check sea water flow, nothing helped. When we last arrived at the boat on a Saturday night prior to a two week cruise in the San Juan's, I decided to take out the heat exchanger to see what it could tell me. When I took off the end caps I got my answer. Bingo!! The raw water intake side channels the water through one quarter of the tubes in the exchanger. They return to the outlet side by running through the other three quarter of the tubes. In doing so, they cool the engine coolant that runs through the exchanger on the outside of these raw water tubes.
Of the ten or so one quarter inch tubes on the inlet side, I could see daylight through one. The others were all plugged with calcified 'critter' remnants. So, what do you do on a Saturday night?? Rad shops are closed, Sunday too. So I very carefully scraped off the debris and used a small wood dowel and a carefully filed round end of a clothes hanger (did not want to scratch or scar the inside of the bronze tubes) to clean out the tubes. I then put end caps on and filled the sea water part of the exchanger with vinegar and left it to soak overnight. Next morning I rinsed the unit, installed it and put on all new hoses and clamps, filled the cooling system with new antifreeze mixture, started her up and watched in absolute amazement the amount of water now coming out of the exhaust. I then cleared the infamous M25XP airlock - on mine always found in the hose returning coolant from the heat exchanger to the engine coolant pump, in that ninety degree elbow hose going into the bottom of the pump.
The engine then ran at 135 degrees F at idle and 165 at hours and hours of cruising rpm. Sweet.
I now need to add a stainless mesh screen into the raw water stainer. I have the stainless cylinder with the one eighth inch holes in it. The critters are getting sucked in through that. In our marina we have these critters about one inch long, one sixteenth inch thick with an exoskeleton - almost like a miniature crab leg. They always lock up my speed transducer's impeller if we don't move the boat for an extended period of time. I now know they do other things too.
The heat exchanger will now be serviced every three to four years - but by rad shop on a planned maintenance basis. We finally left on our vacation and had a wonderful, windy two weeks.

 

[Shadowfax]

Welcome to the M 25 XP club

 

[CaptnNero]

Hot date with the heat exchanger

Thanks for the nice write up of your Saturday night date with the heat exchanger. While my boat isn't overheating, I've noticed a tad bit of steam that I never had on our 32-200 which had the same drivetrain. Now I'll take a look inside the exchanger as you suggest. I think I'll start simple by taking the ends off and putting a light on one side and look thru the other, perhaps with a mirror.

On the 32-200 an impellor once failed and when I went to retrieve the pieces from the exchanger I found a few extras in there !

 

[TorMar]

Follow up on heat exchanger service

Having done the clean up and now knowing what it taught, I would go after the heat exchanger as the first item if I noticed any kind of 'steam' from the exhaust. It is not a difficult job although I would definitely take it to a rad shop for a chemical clean out next time. I did talk to an owner at the marina who had used a .22 calibre rifle bore cleaner rod to do the job. It worked really well, he said.
The only problem I had was re-attaching the long hose from the heat exchanger to the water pump - the one that runs the length of the engine under the alternator. It is a 200lbs psi hose with a 3/4 inch inside diameter, and I swear, the nipples for engine coolant on the heat exchanger are more like 7/8 inch. I had a devil of a time getting the old hose back on. I've ordered 7/8 inch hose at the Pt Roberts chandlery but he still did not have it when we returned, so I can't say for sure, but I micrometered the nipple and it is more 7/8 than 3/4. All the raw water hose is 5/8 inch inside diameter and it went onto the nipples the way it should - very easily. I would get the new hose before taking the exchanger out. I put on new hose because it did not seem to make sense to put back on 17 year old stuff. The other point is be very gentle with the 90 degree elbow hose under the water pump - you may not be able to replace it and then may need to be very creative- this is the hose that forms the air lock.
Finally, the problem with the heat exchanger zinc. Mine was but remnants, just big enough pieces that they plugged four of the tubes on the raw water side. They did come out though.
It seems to me that you can do one of two things - replace the zinc at minimum once yearly, perhaps twice, so it never gets to the point of leaving free floating pieces, or put a non zinc anode bronze plug in and never worry about it again. The jury is out on that one, although some newer heat exchangers do not have a zinc for that very reason. Anyways, for those of you with 'steamy' mist or smoke from the exhaust, this service is a must.

 

[CaptnNero]

zincing the boat

When I unscrewed the zinc a while back there was nothing left and a white plug was left in the port on the exchanger. That was easily dislodged. The tricky part was none of the regular stores around Annapolis carried the right size zinc. For the same M25XP model on the 32-200 they were in plentiful supply. Fortunately I was able to get the right length and diameter and use an adaptor to mate it up to the port size.

I certainly appreciate all of the details. I do happen to have a .22 caliber cleaning tool. I'll let you know how the cleaning affects the mystery mist out the stern.

I'll save the trip to the radiator shop until winter.

Finally, the problem with the heat exchanger zinc. Mine was but remnants, just big enough pieces that they plugged four of the tubes on the raw water side. They did come out though.
It seems to me that you can do one of two things - replace the zinc at minimum once yearly, perhaps twice, so it never gets to the point of leaving free floating pieces, or put a non zinc anode bronze plug in and never worry about it again. The jury is out on that one, although some newer heat exchangers do not have a zinc for that very reason. Anyways, for those of you with 'steamy' mist or smoke from the exhaust, this service is a must.