Bad Thermosensor = Intermittent overheat

[CrankyGypsy]

success.
water tested the replacement sensor today. air temp 72*F and water temp 62*F

after adequate warm-up, it took about 5 miles of WOT to get an overheat. port engine trips the 266*F mark before the starboard engine does, but both showing about the same temperature on the YDS. i love having two of everything on these things for comparison! the overheat did not cause it to go into limp mode, just louder with loss of power. temps would quickly drop with the throttles placed at the detent just forward of neutral and the tripped sensor would reset with the ignition key. the engines were ready to go another run in about 30 seconds - the old sensor would take what seemed like forever to acclimate. did a few WOT passes with the similar results. chalking it up to just running them hard along with 10years of build-up inside the engines.

during the summer, water temps get into the low 80s here, so i'm inclined to believe this will quicken overheats at WOT. but i had success making long runs the first season (i'm assuming the sensor wasn't bad then) if i kept the engines around 9000RPMs. i'm also going to be conscious about making those longer runs with the blowers going.

 

[Cobra Jet Steering LLC]

Boy was the tide high out there today, I think I may hit the water tomorrow.
If your motor is getting loud it means sufficient water isn't getting to the water box

 

[Murf'n'surf]

Forgive me if this was covered previously..... Have you checked/cleaned the raw water intake screen?

 

[Scottintexas]

I'm sorry but I'm confused,

your still getting an overheat?

Shouldn't you be able to run all day long WOT without overheating, I think I have ran for 30 min. WOT without any problem.

 

[4x15mph]

i love having two of everything on these things for comparison!

No doubt!

It sounds like you are still going to look at this more since you should be able to go WOT for hours.

 

[Cobra Jet Steering LLC]

I agree you still have some minor issue with water flow and The first thing I would suggest is to remove the main hose from the pump to the engine and check for obstructions , It should run non stop without overheating

 

[CrankyGypsy]

@Scottintexas the original issue of the starboard having a sensor malfunction causing it to overheat quickly and not reset is fixed. however, both engines are running above 250*F at "extended" WOT.

thanks for the input guys - this is my first boat, so I didn't know what to expect. if you guys are running far longer without issues, I'm definitely going to keep at it.

I have not checked the intake screens, but will do that along with the intake hoses.
unfortunately, they are both running on the hot end at WOT - this had me just assuming it was from prior owners not flushing properly, and the mineral build-up holding heat in. I'd also like to try an extended closed-loop (if I can figure out a way) chemical flush to see if that helps.

 

[CrankyGypsy]

If your motor is getting loud it means sufficient water isn't getting to the water box

it does this along with loss of power only during an overheat error - when the light resets, it's all back to normal. is that not typical? to clarify, it is not limp mode because I'm not limited to 3000RPMs.

 

[tdonoughue]

I have a much newer boat, but I have still never heard of one of our boats overheating on WOT. So I agree with the others that you have some continuing problem.

Given how gooped up your sensor looked (or at least how it looked in the photo), I am wondering if the entire cooling path is not gooed up. I don't know why that would be (I only run fresh water), but I would be very tempted with this type of issue to start with the water box and pull every part I could and clean or replace it. There is some significant blockage somewhere. I am skeptical that a chemical flush will do it on this one. And I don't know that I would run a snake line or anything like that for fear of internally damaging the hoses, etc.

IMHO, etc.

 

[Cobra Jet Steering LLC]

Take a temp reading on the water box " MUFFLER" of each engine when it says it is hot, I would believe due to the sound of the engine your muffler is getting hot on one side and those should have heat sensors that are warning you. You should not overheat running W O T.

 

[CrankyGypsy]

@Cobra Jet Steering LLC I was running with the tray removed and was poking around that area during one of the cool downs to check for leaks. I didn't take a temp reading, but I did feel them with the back of my hand. they were both only slightly warm. there are no sensors on them. the inlets of the boxes were measuring around 90*F on the first test day.

I understand what you are getting at, though. but the loudness doesn't start until it hits the 266*F mark. if I slow down (allowing it to fill, in theory), it will continue to balk at acceleration. as soon as the light goes off, it's fine. yet still, I don't understand this loudness phenomenon for any other reason than what you describe.

 

[Cobra Jet Steering LLC]

I know when my sensor gave me a fit I tried everything, I even removed the thermostat and placed it on the stove in a pan of water with a cooking thermometer to be sure it was opening at the correct temp. I still believe you need to check and clean the hoses and the screen on the jet pump. If you are using lake tarpon I am not familiar with the weed situation there, I know here in the intercostal near Tierra Verde the weeds and sea grass are a constant problem.
Today I was cruising across the flats doing my ski surfing that is where I run about 45 to 50mph standing on the ski , not touching the handlebars but shifting my weight with my arms out to steer the ski, I hit a patch of floating sea grass and the ski dropped 10 mph off it's speed instantly, I would have avoided the weeds had I not been doing the ski surfing and I may not have noticed the speed drop as fast as I did had I been holding on to the handle bars , in any event when I ran into them and noticed the ski slow down instantly I immediately thought of your issue and wondered if perhaps you are just accumulating weeds that are restricting your water intake and since both intakes are aimed in different directions and the props turn in the same direction, one intake may be more susceptible to this build up than the other. I guess when the weather is better I will need to get you over to the Maximo Park boat ramp and see if I can get a handle on what the heck is going on with your boat.

 

[CrankyGypsy]

right now, my gut is telling me the WOT overheats are a heat transfer problem.
i'm getting good/equal/solid water flow from all four pee holes (ruling out intake blockages); the thermostats are both new and there are no hose kinks (i checked); i'm getting good water flow at the end of the main exhaust pipe on the port engine and the water boxes are not getting hot (ruling out exhaust blockage); external and internal temps between the engines are very close* (ruling out electrical malfunctions and water jacket blockages); both engines start, run strong without a hiccup, and will sit rock-steady at ~10200RPMs until the overheating occurs (ruling out mechanical issues).

*the port engine at idle runs 5-10*F cooler in most areas, but i am chalking that up to the ~200RPM difference. the only discrepancy is the external temp of the heads just above cylinder #1 - the starboard engine here is consistently 20*F+ hotter than the port engine ...and yet, the port engine is the one that hits the overheat threshold at WOT first. i've actually seen the starboard's head measure about 203*F here while the port was 176*F after the port threw the overheat warning.

been doing some searching on the PWC forums: i've found a few FX140 and VX1100 with heat exchange problems due to internal build-up of minerals and sand. i actually ran across one VX that had sand in the jackets of cylinder #1, causing overheats. and yet these machines still presented with clear intakes and good pee hole flow. i've had parts of my exhaust off/replaced and noticed there is build-up in the waterways. it's not enough to cause blockage, but i imagine it could cause cylinder insulation.

i do not want to tear these things down to scrape the crud out.

SOLUTION? what i'm thinking of trying is to set up a "closed-loop" flush with Bright Bay Hammerhead Descaler. the Hammerhead is the only chemical flush i've found that says it won't harm aluminum. my idea is to place a large plastic bin under the exhaust port near the jet with a submersible pump. the pump will feed the garden hose flush port (the loop). i'll clamp the intake hose and redirect the pee hole and thermostat hoses back to the bin so there is no fluid loss or trapped air (closed).
there is a $40 pump at Northern Tool that moves 1250GPH (~20GPM). i'm finding the average garden hose delivers about 10GPM, give or take due to friction loss. so that will provide enough pressure, plus extra to hopefully push debris out. looks like the engines will need to run for at least an hour each (constantly monitored via YDS). at idle, any transient, lodged chunks should dissolve without causing an overheat. i imagine dislodged sand will be forced into the waterboxes, but unable to make it out to the bin - so i'll remove those and try to rinse them out post-flush. (https://jetboaters.net/threads/closed-loop-flush-of-mr-1-with-marine-descaler.8443/)

 

[Cobra Jet Steering LLC]

Interesting theory however it is just a guess and sounds like a lot of trouble to go to just guessing. Do the easy stuff first, you should have a thermo sensor on your engine block so perhaps swapping those from one engine to the other may be the way to see if the problem stays or goes to the other side. I also had some wild readings from water getting on some of the electrical connections, so clean and silicon spray as many of those as you can.
Skies do have problems with sand being sucked in the pumps usually from backing off a sand bar etc.
I still believe there is a defective sensor someplace. I know how mine acted and it was very similar , sometimes it would go to limp mode and sometimes it would just flash and sound the alarm, The noise part is very strange but I have heard of internal baffles coming loose inside the water box and causing exhaust valves to burn by causing severe back pressure. I would be looking in the thermostat opening for serious buildup of sand etc. just to get an idea of the water jacket condition, they also have scopes you can feed in the engine to view what it looks like in there, perhaps you can rent one .

 

[CrankyGypsy]

definitely appreciate all the input @Cobra Jet Steering LLC

the intermittent overheats (and long reset times) were the bad thermosensor as you had said, but i'm ruling out all electrical issues for the consistent WOT overheating. both engines/exhaust/waterboxes are reading about the same internally and externally at long idles and WOT runs. the replacement thermosensor on the port engine is tripping the WOT overheats at 266*F, but the starboard thermosensor is around 250*F at the same instance. i also used the YDS to monitor the internal temps during the WOT runs i made last week and both engines are rising at similar rates.

 

[4x15mph]

I would concentrate on the water passage inlets and jacket. I don't know what it is like to take apart your exhaust cooling but I know mine was a mess and required cleaning and clearing of the pilot holes (3). Both sides had clogged and caused overheat problems. I have since added water strainers and I would think this is something even the newer boats would want to consider unless you are confident that the intake screens take care of it.

 

[Cobra Jet Steering LLC]

Totally different engines you have 2 stroke engines he has 4 stroke engines so I don't think it would be a good comparison I have seen a lot of the 2 stroke engines with sand in the water jackets and corrosion etc.

 

[Cobra Jet Steering LLC]

Do you rinse off your engines with fresh water after each use? Or just flush them out?

 

[Cobra Jet Steering LLC]

By the way take a reading of the water temp of the water coming out of the pee holes when the engine says it is hot , this will tell you if there is a difference internally between the 2 engines.

 

[Murf'n'surf]

You say that the motor gets loud........ could you be cavitating slightly at speed and causing your intake to suck in air?