Hot Water Temperature

[KenKrawford]

A couple of weeks ago we took the boat out and motored for 45-50 minutes. Under normal conditions this would produce very hot water but instead it was tepid at best. The engine ran at its normal 165 degrees. A couple days later while plugged in I turned on the water heater and in an hour the water was its normal hot temperature.
Ever since I've owned this boat I've never been able to keep the coolant reservoir full and have never been able to document where it is going. I even had the oil tested to make sure it wasn't ending up there. I removed the radiator cap after the above incident and noticed the coolant level was down slightly so added about 10-12 oz of coolant.
Could the decrease in coolant have allowed an air lock to form in the water heater core? Any other possible reasons for the lack of heat transfer from the engine coolant?

[wolfe10]

"Could the decrease in coolant have allowed an air lock to form in the water heater core?"

Absolutely, Have you tried bleeding coolant line at the water heater. Put a rag under it, have someone start the engine and run it until air is out of the line. The water heater is mounted higher than the engine, so, indeed one can get an air lock there.

When changing coolant, I always have to bleed air out at the water heater.

[Interlude35]

I agree with Wolfe10. I had the same problem with the water heater not being effective when heated by the engine. I removed the engine expansion tank and added a new coolant fill point that is about 2 ‘ above the water heater. It has worked great. It was fairly involved as I replaced the water heater at the same time. I posted most of the details on July 18, 2018 under the title of Engine Coolant Expansion Tank - http://www.catalina350.com/phpBB3/viewt ... Tank#p6176. The existing radiator cap was left in place (14 psi relief pressure) and a 7 psi relief pressure cap was placed on the new expansion tank. John Ferguson, Interlude35(2005)

[KenKrawford]

Brett & John, thanks for your feedback. I've never had an occasion to dive down to the water heater before. Is there a bleed valve or am I going to have to disconnect the coolant line where it enters or exits the heater?
John, your project sounds like an interesting one. If you'd like to email the pictures to me I'd be happy to insert them in your original post. I know Scott Monroe is always looking for articles to publish in our Tech Section of Mainsheet. Consider sending a write up to him for publication as well.

[ElizabethG]

Hi Ken,

I was at the boat this w/e to change the coolant. There is a petcock on the thermostat, one on the bottom of the heat exchanger and one where the water hoses go to the water heater. You might need to "burp" all three. BTW, check all the engine hoses for leaks while in there. I found my exhaust hose had a small water leak, but that is on the raw water side of the equation.

I think you mentioned that you have never been able to keep your engine expansion tank filled. After you burp the system and you still have the same problem, you'll need to keep digging.

I'm assuming your oil is not a "chocolate milkshake" color. Coolant mixing with the oil.

You can also borrow a "block tester" from Advance Auto (tool loaner program) to see if there are exhaust gases in the coolant. Check out YouTube on how to use. Either one of these conditions could be indicative of a head gasket issue.

If you need help, let me know and I'll be glad to meet you at the lake.

Bill

[KenKrawford]

Bill, thanks for the info and the kind offer. I've used a pressure tester to test for leaks but never a block tester. I'll put that on my "to do" list. The oil appears perfectly normal to the naked eye when I change it. Would a lack of coolant in my oil analysis rule out a cracked block or leaking head gasket or is it still possible?

[ElizabethG]

Hi Ken,

I know enough about the M35B to be dangerous...

If your oil looks OK, then that part of your head gasket should be OK. If the block test shows positive for exhaust gas in the coolant, that could still be a head gasket issue. This is all worst case as these engines are very robust.

If after burping the system of air and you still have the coolant reservoir not staying full, then there has to be a leak somewhere as it is a closed system. However, you mentioned that you did a pressure test and that was OK, so I'm scratching my head...

Hopefully, someone else will jump in with ideas...

Bill
Atlanta, GA
#193

[leigh weiss]

A while ago I mentioned a small coolant leak that was very hard to find. It was one of the two screws/bolts ( the longer one) holding the alternator bracket to the block where one of the threaded holes went into the water jacket. A small leak that evaporates because of the heat of the engine leaving no trace in the engine pan plagued me for a while until I used thread sealer on the threads and re-torqued the screws. No more leak and the coolant tank stayed full ever more!. This might be the case for you as you seemed to have checked out all other root causes. Let us know if this is the case.

Good hunting.

[tmh]

I had a similar situation of a constant small coolant leak that was very difficult to track down. Lasted for several months. Eventually, had a good diesel mechanic look at it and he suggested that I replace the overflow expansion tank. He thought it had a small crack in it. And he was correct!
Solved my problem
Just an idea.
Mike

[ElizabethG]

Ken,

Just one more thought...

How about a UV dye leak detection?

Bill

[KenKrawford]

Never knew about this. I assume some type of fluorescent dye is added to the coolant and then scan the system with a UV light?

Ken,

Just one more thought...

How about a UV dye leak detection?

Bill

[ElizabethG]

Hi Ken,

Yep, that's correct.

Bill