2QM15 still over heating after...

[dailytrek]

I'm stuck with resolving my over heating problem. My engine is a 15hp Yanmar (2QM15). I have changed the impeller and thermostat, flushed out the sea water intake from the filter back to the thru hull, cleaned out the sea water filter, cleaned much of the barnacles off my prop and removed most of the carbon build in the exhaust-water discharge mixing elbow. The mixing elbow had a heavy build up of carbon which I was able to remove most which extended the overheating issue from 15 minutes to over an hour and a half. It didn't overheat until I raised the rpm from about 1000 to 1200 which occurred after about 30 minutes. The boat had been motoring at about 4 miles per hour at 1000 rpm and about 5 mph at 1200. The sea water exhaust mix expelling from the boat seems the same as what I note in similar sized engines.
Since the cleaning of the elbow helped considerably, would it be helpful to go the aftermarket version without the elbow and assure best possible flow?

 

[Davidasailor26]

5 mph at 1200 rpm? I don't know the max rpm of that engine but that sounds WAY overpropped. You might be lugging the engine. What is the max RPM in neutral? You should be able to achieve close to that same amount in forward.

 

[Bill Roosa]

Your diagnosis sounds correct. Check the elbow raw water tube. That can get carboned up also. David makes a good observation too, 5MPH at 1200 sounds over propped. That could be a tachometer problem too...... and running at a high RPM will cause overheat. Most of these motors have a "max sustained RPM" and a "1 hour max RPM" Running for more than an hour above the 1hour RPM is not recommended. If the tack is not reading right you could be fine and just over taxing the motor (with a correctly pitched prop)

 

[Davidasailor26]

Bill makes a good point about the tach readings. If the max RPM in neutral reads close to 1200 get an optical RPM sensor to find out what it's really turning.

One other thing - how is the water flow out the exhaust? It sounds like you've check most of the usual clog points but you don't know for sure without seeing the water flow.

 

[kloudie1]

Daily Trek. here is a link to the shop manual for the engine.. http://j30.us/files/2qm15_servicemanual.pdf
You should be able to get to 3000 RPM (real RPM, not on Yanmar tacho).. A quick look at the manual shows that there are two gear ratios with that engine, you nay have the higher and a prop from the lower? or a mismatch like that.. An optical tach is cheap and you could share one with a dockmate? these are accurate "enough" for troubleshooting:
https://www.amazon.com/s/ref=nb_sb_...optical+tachometer,aps,190&crid=2ISCKQMPR2OIH

 

[The Shadow Knows]

D.
I'm not familiar with your specific engine so, I did a quick look-see search for a heat exchanger on your engine.
I did see a few pics. I don't know the engine age, but if you have cleaned areas & did an impeller check, I can only think of a few other areas of concern.
My boat lives in saltwater & I have had problems with crustacean growth in the thru-hull tube. There is also a strainer onboard, check to be sure this is not the problem.
I do know that heat exchangers can clog from age and/or a bad impeller breaking off pieces clogging the tubes and/or the motor passage ways.

As for the best approach to these, I would think it best to do some background study for troubleshooting engine & your specific boat cooling system.

Good luck.

 

[kloudie1]

Another thing to check is the bypass hose to the water heater (if a heater is fitted).. if that hose becomes restricted, water flow could appear normal but flow through the engine could be restricted. The hose between the cylinder head and exhaust manifold is normally routed through the water heater before going to the exhaust manifold.. if the engine water coil in the heater is fouled or the hose is kinked/restricted, the problem could be there.. (chapter 7 page 1 in the PDF shop manual from post #5.) no heater is shown in the diagram but the hose from the cyl head would go there, then back to the exhaust manifold.

 

[rardiH36]

Yes ... all of the above suggestions.

Here are a couple of others. I expect your 2QM15 is direct seawater-through-engine-block cooled (not antifreeze circulating through a heat exchanger). If so:

1) It's possible through the years that deposits/scale have built up inside the block's water passages. I have seen some references on the forum that it is possible to clean out. Others say not possible. So it will be your sleuthing to discover.

2) Is the engine really overheating? Or is it just the alarm sounding? I mention because it was an issue for me. My 2QM20's alarm was sounding although my temperature gauge was showing only 140-145F. This for me would tend to occur 30-60 seconds after running the engine at 80-90% for a while then throttling back to idle. Or when starting the engine back up after a short shut-down. After a couple of minutes, the alarm would go off when the sender reset. Considering the anti-freeze cooled QM's operate at the +/- 170F range, 145F is nowhere near a dangerous level. (But operating temp of less than 150F is required for seawater cooled engines to prevent mineral deposits inside the engine's circulation system. ) My theory as to why the alarm: Latent heat from around the cylinders would heat the water above the alarm trigger point as the heat radiated towards the now still water.

The seawater cooled alarm senders for both the QM20/30's and the 2QM15 are rated 60c on (triggered) and 56c off (reset). (This Yanmar sender is coded with a Yellow Dot on it.) The seawater cooled senders for the GM series engines are rated at a higher 65c to trigger on. (They are coded with a White dot.) So the alarm for GM engines cooled by the exact same seawater as the QM's won't sound until the temperature is about 9F higher.

I replaced the Yellow dot alarm sender with a White dot sender. And the nuisance alarms did stop. The seawater cooled thermostats for the both QM and the GM engines are rated the same: 42c (open) and 52c (close). It's only the alarm trigger points that are different between the two engine series. Just conjecture here, but perhaps when Yanmar released the GM series to replace the QM's they noticed more alarm trigger "headroom" (an extra 9F) was required?

 

[dailytrek]

Wow, what an amazing response. Thanks!
Davidasailor26 Over propped? I plan to have a diver clean my prop and look for the exact prop specs on it. It is a folding two blade version. I can then begin discovery if I'm over propped.The engine runs fine at 3000 rpm in neutral. The water expelled from the exhaust seems typical for my boat but its my only motorized sailboat I have owned. How can I discover if my water expulsion is normal? Send video to expert on my engine?
2. Bill Roosa The tach is new and I calibrated it but will recheck. I feels like just above idle so I think its correct.
3. The Shadow Knows I have checked the salt water filter but will have the diver look on the thru hull.
4.kloudie1 No water heater or coolant on this boat
5. rardiH36 I do think the engine is overheating because I see some vapor in the exhaust and the alarm only comes on soon after I push the RPMs up a bit. I had not noticed any overheating for the first year I had the boat because I didn't motor very much. I will keep in mind about the water passages being blocked.

 

[Davidasailor26]

If you can get 3000 rpms in neutral the tach is probably close. I'd think you could cruise in the low 2000's if the max is around 3000. If a diver is going down anyway have him try to check the diameter and pitch of the prop. Not sure how you could find out what they should be for that model boat though.

 

[Benny17441]

When you replaced the impeller, where any vanes on the old one broken and perhaps missing? Pieces of a broken impeller have been known to get lodged in the raw cooling passages and slow the flow of sea water. How is the discharge flow?

 

[dailytrek]

The impeller was complete. The discharge seems normal but I cant truly determine if its adequate.

 

[Rob2435]

Try running some Salt Away thru your system, increased the flow rate on my boat.

 

[dailytrek]

I found a video of an engine like mine on YouTube and the water expelled from the exhaust seemed more continuous than mine. When I back flushed my system, I did it from the sea filter out which didn't include the engine and associated hoses. I plan to remove my impeller and backflush my cooling system from the furthest point which is the hose to my exhaust mixing elbow.

 

[jibes138]

Try replacing the thermostat. Maybe it is not opening fully or at all? You can test it by putting it in a pan of hot water and see if it opens.

 

[rardiH36]

I found a video of an engine like mine on YouTube and the water expelled from the exhaust seemed more continuous than mine. When I back flushed my system, I did it from the sea filter out which didn't include the engine and associated hoses. I plan to remove my impeller and backflush my cooling system from the furthest point which is the hose to my exhaust mixing elbow.

Never done it so I don't really know. But something I might have read at some point. That is be careful that your flushing of the system doesn't allow water to back flow into your exhaust manifold. And possibly flood the cylinders. Water in the cylinders doesn't compress as the air/diesel mixture. So cranking water filled cylinders with the starter motor causes havoc. I am somewhat recollecting people commenting that they have seriously damaged their engines.

Maybe someone else on the forum can comment.

 

[heritage]

Read today a good article in Good Old Boat about chasing down a suspected overheat problem. He had a engine temp gauge that over the months began to show higher temp readings. The guy spent hours checking out the usual suspects. His last check was with an IR temp gun looking for some hot spot on the engine that might help solve the mystery. It worked, but not in the way that he anticipated, he aimed it at the temp transducer.. it showed 170 while his engine gauge was reading over 190. He replaced the transducer and readings returned to normal.

 

[dailytrek]

Thanks again for all the input. I already replaced the thermostat and the old one was quite gunky. I am certain I am overheating as I'm getting some vapor in the exhaust when the alarm goes off.

I again back flushed the sea cock and saw some barnacles flushing out under my boat. I have not gotten the diver out yet but I expect there may be a bit more around the thru hull. I removed the hose after the filter and before the pump and its slightly collapsed and has a necessary hard bend due to its location, so I will replace. It has a slight build up inside. Newer hoses didn't show this build up. I ordered an aftermarket SS exhaust-sea water mix that goes after the manifold. I plan to use Barnacle Buster and backflush my system since I'm seeing build up in hoses and at the thermostat. I'm optimistic I'm on the right track now.

 

[dailytrek]

Great News! My overheating problem is solved. As I last posted, I changed a couple older hoses and flushed my system with Barnacle Buster. The flush was simple, effective and inexpensive. Barnacle Buster recommends a flush system with a pump, hoses and a bucket for over $400. I bought a bilge pump ($25) on line at Walmart, used on old plastic bucket and bought clear hoses at Home Depot ($10) plus a pair of alligator clips to operate the bilge pump ($10). So along with the gallon of Barnacle Buster ($30) I spent $75 and now my engine is running smoother, starts quicker and doesn't overheat at hull speed for extended periods. The amount of grey sludge that came out of my engines was hard to believe...about a half inch settled in the bottom of a gallon bucket. The flush apparently improved seat water flow and great improved the transfer of the cool ocean water to the engine.

I attached my clear hose from the bilge pump to engine tube where my cooling water enters the engine. I removed the thermostat and installed a return hose from the tube which would normally lead into my exhaust mixer. I wrapped window screening around the hose which ran back into the bucket from the engine to catch any larger pieces of ocean crustacean. I observed white chucks in the screen which eventually dissolved into grey muck. I ran the solution flush for 4 hours then replaced the 1/2 gallon of solution with the second half of the jug and ran for another 4 hours. After which I flushed 3 times with fresh water. I think this is a great idea for any marine water cooled engine which has not been flushed out in a few years. Thanks for all your help. I hope this posting helps you in return.