overheating 1985 oday 35

[wildegroot]

Husband and I are new sailors. The plan was to get our boat in good shape, then have fun learning to sail! We never got the engine overheating problem licked and husband is ready to sell his baby. So far he's changed the HE to a recommended upgrade with a 3" hose, changed/topped the coolant, bled the coolant lines, made sure the strainer is clear, installed new thermostat. Checked and changed the hoses that got damaged with the overheating. Twice we overheated and had to be towed. I said, 'No more! This is not fun!' Went out this morning and bang, started smoking after 20 minutes going at low speed. What else can we check? My captain loves his boat and I just want to have fun, not quit!
TIA anybody

 

[JoeWhite]

How about the water pump?

 

[kappykaplan]

The only thing I don't see on the list of things that you've checked is the impeller.

 

[jssailem]

The water pump and impeller would be among the usual suspects.

Have you tried to flush the coolant side of the engine?
You tell us you have an ODay 35, but not the engine brand you are struggling with.

Is it the M25 Universal or has a former owner put something else in the boat?

 

[wildegroot]

Hello everyone. We have had overheating problems in both water circuits of a Universal M25 engine. When the engine is running, the saltwater system spews spurts of warm water out of the exhaust outlet on the stern and every thing is fine until opening the throttle more and within a few minutes the exhaust hose is burning up. All the hoses were replaced. The salt water screen basket is clean. When I pull the feed hose off the ball-valve on the bottom of the boat, salt water flows into the bilge reasonably fast. I replaced the entire saltwater pump. I cleaned out the heat exchanger and when that didn't help I upgraded to a 3 inch diameter heat exchanger. On the fresh water/anti-freeze side I wanted to test the thermostat even though the gauge never showed high temperatures. When I finally got the very rusty M6 bolts out of the thermostat housing, I discovered that one bolt was just sort of glued into the threadless hole in the block. Luckily I was able to install a longer bolt and install a hex nut under the mounting flange. I boiled the thermostat on a stove and it seemed to open at the tight temperature but I didn't have the right thermometer so I installed the new thermostat I had already bought. As far as I can tell, the green system is properly bled. I also over filled the plastic coolant expansion tank and installed a small ball valve in the bleed hole in the top of the thermostat housing to make bleeding easier. I'm still having breakdowns and getting ready to sink the boat.

 

[JoeWhite]

Is the mixing elbow clogged?

 

[Davidasailor26]

Since you’re burning the exhaust hose and not reading high temperature on the gauge I don’t think the fresh water side is the problem. The exhaust hose should be cooled by the raw water, and lack of raw water getting through the mixing elbow is the only thing that would let the hose get that hot. It sounds like you’ve already addressed everything along the raw water circuit except for where it empties into the mixing elbow. Those elbows are more common problems on Yanmar’s than Universals, but at this point that’s where I’d look next.

 

[wildegroot]

Thank you for responding! I'm used to working on cars not boats. What is a "mixing elbow"? I'm also convinced that the burning exhaust hose problem is not in the fresh water/antifreeze circuit but water is squirting out the back of the boat about every one or two seconds. Some squirts hit the sea about three feet away and some more like ten feet. That makes me think the flow is OK but what do I know? So, the mixing elbow gets clogged and this is a common problem? Clogged with what and how do I unclog it? Thank you!

 

[kappykaplan]

The mixing elbow is where the hot exhaust gases from the engine are mixed with and cooled by the raw water that passes through the heat exchanger. Then everything goes out the exhaust.

 

[Davidasailor26]

Follow the hose off the exit from the heat exchanger and you’ll see where it empties into the mixing elbow, before the exhaust goes into the muffler. If everything is working properly the exhaust should be only around 100F below the point where the raw water is injected, before the transition from pipe to hose. Over time the elbow may have gotten clogged with soot from the engine meeting the salt water.

 

[jssailem]

Check out this video on the exhaust elbow.

 

[dlochner]

At low rpm and with an unloaded engine, such as when idling there is probably enough water passing through the elbow to give the appearance of the elbow not being blocked. At higher speeds and under loads the exhaust temps will reach 800° or more, lots of water is needed to cool the exhaust. You should notice a significant increase in water flow at higher speeds, if not a clogged mixing elbow is likely the cause of the problem.

The combination of hot exhaust and water form a corrosive mixture. Repairing the mixing elbow is usually not an option as the metal is corroded beneath the carbon build up.

HDI Marine makes stainless steel mixing elbows for many engines. Go there for a replacement.

Stainless Steel Exhaust - HDI Marine

Cast 316 Stainless Marine Exhaust Components - Engineered To Be Better

hdimarine.net

 

[Stu Jackson]

Agree that what your issue sounds like is the hot raw water from the HX is not getting through the mixing device. John's video shows a mixing elbow, but you should know that many M25s, like on my C34, came with a simple pipe nipple into the exhaust hose before the muffler, which we call an exhaust riser.

They look like this:

On my 1986 boat, I have replaced the exhaust riser three times and the exhaust hose once.

You might find this handy, too:
Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too This includes a link to the Critical Upgrades topic which has more engine information please read it too.

Diesel Engine - c34.org

 

[Ralph Johnstone]

The final two second acid test I have always used is that the mixing elbow should be no more than warm to the touch at WOT. Anything much hotter indicates a blockage on the water side.

 

[wildegroot]

Thank you everyone for all the advise. I'll look into the mixing elbow situation. Thank you again!

 

[wildegroot]

Well, I think you gentlemen steered me in the right direction and to take a close look at the mixing- elbow. I removed the whole home-made assembly and, with everything still together, it looks like the passages are clear. I don't want to disassemble it until I record all the dimensions in case I decide to make new parts. As of right now I haven't found a replacement for sale online.

What I did find, now that I understand the system a little better, is that on the present, partially homemade, mixing elbow is that the 5/8 inch pipe that injects the saltwater into the exhaust stream is flow-wise beyond the 1-5/8 inch exhaust-hose that always fails on our boat. So, no matter how much water is flowing, it never cools the horizontal exhaust hose and it burns up. I wonder if someone had it apart and assembled the parts in the wrong order?

I feel kind of stupid for not figuring this all out by myself but I just assumed it was supposed to be like it was. I need to place the water injection before the exhaust reaches all the rubber exhaust hoses. I really think I've found the solution. Thank you for all your very helpful advice! I'll let you know how I make out.

 

[dlochner]

Oh yeah, that's wrong. And it is probably not original.

Water needs to be injected before the rubber hose and it should be positioned such that water can not back flood into the exhaust manifold. That's why I have the 180° elbow and what the PO was trying emulate with the hose in the middle of the system.

For comparison, the riser on the left is a copy of the factory's original and the one the right is a homemade one after the original failed at the beginning of a cruise and I had to get home. This was on a 1981 Sabre 30 with a Volvo MD7A motor. All of the parts in both are black iron and available at any big box HW store except the 180° elbow, McMaster-Carr has them.

 

[Stu Jackson]

1. As of right now I haven't found a replacement for sale online.
2. is flow-wise beyond the 1-5/8 inch exhaust-hose that always fails on our boat. So, no matter how much water is flowing, it never cools the horizontal exhaust hose and it burns up. I wonder if someone had it apart and assembled the parts in the wrong order?

3. I feel kind of stupid for not figuring this all out by myself but I just assumed it was supposed to be like it was. I need to place the water injection before the exhaust reaches all the rubber exhaust hoses.

1. I found this years ago, don't know if it is still available. Many folks cobble together their own exhaust risers.
Westerbeke Nipple Source NIPPLE - Westerbeke

2. Yes, it should be ALL insulated metal up to the injection nipple.

3. Don't blame yourself. Unless you made it! Many of us bought boats that had dubious stuff done by a PO. Catalina Direct offers pre-made exhaust risers, usually dimensioned for Catalinas. Try them, they might have one for you.

Good luck, glad we could help. BTW, that BLUE HOSE is called hump hose, and should be used. Noodle around in the link I gave you earlier; saves the inlet port of your muffler by absorbing shock.

 

[Richard19068]

Good find. That section between the elbows should be iron pipe, not rubber. If the rest of the metal is in good shape you might be able to just replace that piece. But the elbow on the manifold side looks a little iffy in the picture.

If you rebuild I would use black iron pipe, not galvanized.

 

[wildegroot]

Great! Thank you for the advise and support. By "blue hose" do you mean black exhaust hose with the blue stripe?