Engine Overheating

[Tad and Toby Jackson]

I hope this is a problem is one that someone has addressed before: Toby and I took the Comfy Dory down to Ft. Pierce Inlet on Friday the 10th from our home on Merritt Island. The run is about 74 miles and we cruised at about 4400--4500 RPMs which about 19.5 to 20.5 mph for our boat loaded. The engine ran fine for about 2 hours or so and then suddenly throttled down to idle speed and the temperature light/buzzer went off. I checked the pee hole and there seemed to be a strong flow, although it flared a bit, but I went ahead and rodded the opening which made it flow in a steadier stream. This took only a couple of minutes and then I throttled back up and was off again at cruise speed...no problems for the rest of the trip down.
We had a great weekend swimming, fishing and generally watching the crazies that congregate there on the weekends. We spent our nights a mile or so north of the inlet on the ICW tucked behind some "spoils" islands. Very relaxing.
We left for home about 11:00 AM on Sunday and had a great cruise, again at about 4400 RPM's. We had cruised about 70 miles and were nearly in sight of our dock when the engine throttled back to idle speed again and the temperature light and buzzer went off. I tried rodding the hole again and then attempted to throttle back up, but the alarm went off at about 1400 RPM's. Since we were so close, we went ahead at idle speed and although slow, we progressed along fine at 1300 RPM's. If I tried to accelerate back up to speed, it would alarm again. When we got about 1/2 mile from home, the temp light went out and we were able to throttle back up again without the alarm.
So far, in discussions with boating friends, the consensus seems to be the thermostat as the villain. This is a 2004 Honda 75 HP carbuerator engine. Is there also a sensor of some kind that could be the problem? I think I will go ahead and change out the thermostat anyway since I've had the boat for 2 years now and have never changed that out.
Any suggestions or comments would be appreciated.

Thanks...Tad

[Ashley Lynn]

Tad,

Last spring I had experienced the same symptoms you have described on my 2007 Suzuki efi 115. After the engine would drop down to idle and the alarm would sound....I would check motor and all seemed well...nothing clogging the water inlet nor the outlet.

I had Doug/Service tech at Wefings go over the motor(thanks to Marc)..with me being there to watch and learn. He checked sensors, thermostat and some type of actuator/switch. We took the boat out for a couple hours hooked to his computer and we could not get the problem to reoccur. The only thing that was shown on the computer statistics is a "gradient temperature" which Suzuki told him that once the temp gets to a certain threshold it will record it----but it is not supposed to shut the motor down.

We replaced the water pump and impeller since we had the motor broken down and It was about time for the change......

The only thing they thought could have caused it was that something got caught on and covered the water inlet....grass etc....I dont know....but anyhow.....I have not had the problem reoccur since spring 2008.

[matt_unique]

Perhaps a degraded impeller pump limiting water circulation? I would start there unless it was changed recently.

[Tad and Toby Jackson]

I had just replaced the water pump impeller approximately 10 hours ago and it has run fine since then. I had done that replacement because the same shut down happened once before and I too thought it might have been a worn out impeller, but the old impeller was in good shape.

Tad

[Sea Wolf]

Look at the possible culprits and the probability that they are causing the problem:

Thermostat- could cause overheating, but not likley it would be sporadicc and intermittent.

Temperature sensor- more probable, but why would it be intermittent, returning to normal? Still possible, though.

Water pump-problem would not occur not intermittently, but anytime motor was run above a certain rpm range, or into warmer water.

Clogged Passages/Water Intake- This is more probably the problem, getting clogged with floating debris, such as plastic bag, some sort of plant or animal material, etc. I know that the water pump will crew up a lot of the stuff we fear as boat operators, but a single piece of plastic can cause a big time melt down of your engine block if the emergency high temperature and rpm limiter system fails.

Next time it happens, slow down, carefully shut down the engine, and tilt it up and see if there's anything blocking the water entry(ies), doing so in such a manner as to be able to detect it before it floats away.

Just my 2 cents, worth what you paid for it!

Joe.

[thataway]

We had 3 episodes of alarm, and drop to idle--and all were related to kelp/week. If that happens, we always stop the engine, then back down, and make sure that the lower unit is clear. As Joe says, the other possibilities are less likely.

[starcrafttom]

I had this happen several times on our last trip. First think I do is stop the boat and put the boat in reverse and hard over on the wheel for a few seconds. this will clear off any weeds. Then forward at a slow pace and then full throttle. cleared it up every time. just slowing down but still going forward will not clear the debris off.

[Tad and Toby Jackson]

Brats,

I wanted to follow up on this posting from July regarding the shut downs to idle speed and the overheating alarm on our 2004 75 HP Honda. The problem continued during our trip down to the Keys in August, but not too often. We spent 2 weeks and traveled 767 miles round trip, and the problem still happened, but not too often as to cause us to have to shorten the trip...just had to stay below about 4300-4400 rpms to avoid the shut downs. We were not able to flush the engine during the trip. Since we returned, we have taken 2 other trips on the ICW to Ft. Pierce and to Sebastian Inlet. The problem was still there and the maximum rpms has dropped to about 3800 to avoid the idle downs.
I went to our local Honda dealer and spoke with the mechanics and parts guys and the consensus was that it was probably either the relief valve or the flush valve that were the culprits. Those parts are only $7 each so I got them as well as new rubber gaskets and did the work this past Sunday.
First one that I worked on was the relief valve which is located on the port side of the engine below the thermostat housing. From it's name, I assumed that it would be the culprit, thinking that it was not relieving pressure built up from overheating. The valve and housings and hose nipple were in great condition with very little salt corrosion build up, but I changed the valve out anyway along with the rubber gaskets.
The second one, the flush valve, is located at the top rear of the engine 90 degrees around from the thermostat housing. When I removed the cover, I FOUND the problem. The housing, hose nipple and other spacers all the way to the engine block were packed with salt corrosion. The diameter of the hose nipple which about 3/8" ID had been reduced down to about 1/8" diameter and quite obviously was not allowing much flow. The plastic valve and spring were coated with salt corrosion too and probably hadn't been seating itself as tightly as it should have been. I cleaned all the housings and hose nipple and then installed the new valve and rubber ring washers and then ran it for 30 minutes on the garden hose ears. No problem there, but of course I was not able to get the rpm's up to the shut down range, so it will require a check out ride this weekend to see if the problem is fixed. Keep your fingers crossed for me!
The only other part that the Honda guys said it might be is a Thermostat switch assembly that is located near and slightly below and to the rear of the relief valve housing. That part costs $70 and the Honda guys suggested I try the other 2 valves first. I did pull the Thermoswitch just to see what it looked like. It screws into a dead end hole into the engine block and I assume that it reads the heat build up in the block. It looked like new, especially since there is no water that passes by or through it, so I re-installed and will not replace unless the valve replacements do not do the trick.
I'll check back in after the test ride, but I feel pretty confident that I have found the problem. Maybe this can help others with a similar problem...at least something to check for those who run in salt water a lot.

Thanks...Tad

[marvin4239]

Hi Tad,
I had a similiar problem a couple times with my Suzuki and started checking what I knew to check and in my service manual I found that the head has internal anodes in it. I pulled the cover just two bolts looks sort of like a thermostat cover and the anode was about 1/2 rotted away and the cavities were completely full of salt even though I use Salt Away. On the other hand the thermostat looked like new. Don't know if the Honda has internal anodes but replacing mine seemed to fix the problem except for as Bob said twice I got grass blocking the intake.

[Bill3558]

Hey Marvin, do you have a Suzi 115?

I have the same problem. Can run for hours and then it will do the overheat shutdown to 1800 rpms or so. Stopping the engine and restarting has so far resolved it, but I am trying to figure out why. I have replace the thermostat and water pump, but it still does it. I need to look into this internal anode thing.

[marvin4239]

[Tad and Toby Jackson]

Well, here I am again with the overheating problem. A short re-cap of the things I have done to try and eliminate the overheating problem. I replaced the impeller first...not the problem. I replaced the thermostat next...not the problem. I replaced the flush valve and the relief valve and thought I had solved the problem since the flush valve was salt encrusted...not the problem. Last item that I knew to replace was the thermoswitch which reads the overheating problem...again, not the problem. I replaced the plugs too, just because I couldn't think of anything else to try. Still overheats at about 4400 rpms. I went to our local Honda dealer, Boathouse Marine in Melbourne, FL and spoke with the head Honda mechanic. He was very helpful and said he had just worked on a Honda 50 a couple of months ago with the same problem. He had replaced all the same items that I had and the problem still persisted. He said that the last time he worked on the 50, he pulled the water jacket cover and found that the water jacket itself was salt encrusted. Suggested that I use On & Off as a solvent to clean the inside of the water jacket...but don't leave it on too long as it is basically an acid. I have ordered a new water jacket cover gasket ($33) and it should be in today or tomorrow so I will turn some wrenches this weekend I hope and pull the jacket cover and see what is inside. Mechanic said the 50 HP had not had a problem since he cleaned the water jacket, so maybe I will get lucky this time...after all...what is left to change out?

Anybody else had a problem with salt build up in the water jacket? I flush the engine with fresh water for about 30 minutes whenever I bring it back home after a weekend or a week. We do have it in the salt water for a week or more when we take trips and had it in the water for more than 2 weeks last summer when we traveled down the ICW to the Keys. That is a long time to go without flushing and I suspect it is those times that allow the salt corrosion build up.

Tad

[Sea Wolf]

Tad- Good luck with your motor, sounds like you're on your way to a solution.

This brings up a fundamental question, at least it seems so to me, which is

"Will simple fresh water flushing, on a regular basis, dissolve salt deposits in an outboard motor, or do those deposits, once formed, resist simple dissolving with fresh water, and gradually accumulate anyway, and, if so, what is the best way to go about removing them, and what products or chemicals are best suited for the job?"

We've got some outboard mechanics and dealers on board here, and should be able to get some pretty good answers, though I suspect there are a lot of complicating issues to a fairly simple question. I'll start a new thread, so I don't hi-jack this one, OK?

Joe.

[DickAndSharon]

We had the same issue with our 135 Honda last summer. Rather frightening when running 3-4 footers in the Baltimore shipping channels.
Shut the engine off, raised it, and saw a plastic bag come off the lower unit.

[Tad and Toby Jackson]

Well, here I am again, but at least the problem has been solved. You can read in my previous posts all the things that I have tried to solve the overheating problem. None of those things solved the problem, but at least I got to know my motor real well. I finally took it to the Honda dealer because the next thing to try was to pull the head and see if the head gasket had been compromised allowing hot exhaust gases to get into the water jacket and heat up the water that is supposed to take the heat out of the block. I just felt that was a bigger project than my skills could take on.
The head mechanic worked on it and when I went by to look at the progress, I was glad that I had not tackled it...parts, pieces and bolts everywhere! Unfortunately, the head gasket had not been compromised. He eventually boiled (his word) the head and block and said that there was quite a bit of salt crud that came out to the point that he could now see the inside paint in the water jacket. He soft ground the head and cylinders, cleaned everything and then put it back together with all new gaskets and did a water trial on it. He ran it at WOT for about 15 miles and it did not overheat! Finally!
Bottom line? $1798.87! He said that they have seen this problem more and more in the Hondas, Yamahas and Suzukis or for that matter any engine that is primarily run in salt water even though they are being flushed after use. I am thinking that there must be a way to introduce a product like Salt Away into the flush water. Any suggestions? Maybe something like a Miracle Grow fertilizer dispenser modified to connect to the flush attachment that fits into the rear of the engine?

Tad