Overheat Warning

[ahill]

Recently had new water pump impellers installed on the 225 OX66's on my Sailfish by a Yamaha mechanic who has done this 3 times for me.
The over heat warning on the port motor has sounded twice.
Once when leaving the motors in gear while I connected the winch cable to the eye.
And this weekend when idling in gear.
After switching off and cooldown the motor cranked up and ran with no problem.
Both times the rpms were at 500. At 600 & above I don't have the problem.
Any suggestions on a cause?

 

[Grog]

How old is the poppet and the t-stats?

 

[ahill]

Thanks,
I've had the boat since 2006 and unless they were changed by PBMC, which did a lot of predelivery maintenance, they are probably original 1998.
I thought that if one of those failed it would affect the full rpm range.

 

[cgmiller]

As Grog mentioned, you may be having a problem with a tstat or poppet valve not opening all the way and at low RPM you are not getting enough water flow or pressue to keep the engine cool. If you have not replaced them, it is time to do it.....

 

[Doc Stressor]

A bad poppet valve is often a cause of overheating at low speed. It has little effect on temperature at high speed.

I would bet that this is your problem.

 

[Grog]

Yea, if it's original the culpret is most likely the poppet. If it can't seal well enough, at idle too much water bypasses the motor and you run hot but when running there is enough perssure for for motor even bypassing some of it. 2 bolts, new gasket, o-ring, plunger and spring, it's an easy job. Don't ignore the t-stats, change them too but be VERY careful the bolts don't snap. To be honest that's one small job I'd have a pro do if they haven't been changed in a long time. They know how much pressure the bolt will take (it's Aluminum) and when to use heat and how much.

 

[ahill]

Thanks,
All signs point to the poppet valve. What is the Yam part name?
I'll try Locktite new product Freeze & Release instead of heat.
Touted heavilly by Ship Shape TV.
Should I shoot Saltaway up thru the galleries as well?

 

[seasick]

You didn't mention if the pee stream is strong at idle. Although poppet is possible, the fact that this occurred after replacing the impeller leads me to think that there is a problem with the repair. I suggest that you contact the mechanic.

 

[cobrapowersys]

Had the same problem on my 268 islander w OX66 250hp. I don't think it is the poppet. If those tstats are from 98. Def change them ASAP. Also you may have sand in your weep hole. If those two don't work it's your poppet valve.

 

[Enough Already]

I had the same issue and ended up taking off the heads to find lots of crud and growth in there, plus broken-off chunk of anode blocking the main water path. Changed poppets, springs and t-stats while I was at it. Big job but not difficult. Zero isses since then. I posted up the whole project here - http://www.thehulltruth.com/boating-for ... heads.html.

Maybe overkill but I know a lot more about my motors and feel really good about the repair.

 

[ahill]

If the pee stream is strong ( sound like a Urologist) can the p valve or t'stat still be the problem?

 

[Curmudgeon]

If the pee stream is strong ( sound like a Urologist) can the p valve or t'stat still be the problem?

On a Honda, the tell-tale comes off before the stats. Designed that way so operator will know the pump is working from start-up. Don't know about Yamahaha. One question, was the motor really hot ...

 

[seasick]

If the pee stream is strong ( sound like a Urologist) can the p valve or t'stat still be the problem?

On a Honda, the tell-tale comes off before the stats. Designed that way so operator will know the pump is working from start-up. Don't know about Yamahaha. One question, was the motor really hot ...

This why I asked about the pee stream. If it is weaker than normal, there is either a blockage in the pickups or something wrong with the impeller replacement.
I find that coincidences are rare. If you didn't overheat before the impeller job and do now, you can be pretty sure the work had something to do with it.

 

[seasick]

If the pee stream is strong ( sound like a Urologist) can the p valve or t'stat still be the problem?

On a Honda, the tell-tale comes off before the stats. Designed that way so operator will know the pump is working from start-up. Don't know about Yamahaha. One question, was the motor really hot ...

 

[ahill]

I didn't notice if the pee stream was strong. I checked at the dock before heading out and they were equal & normal.
The motor did not get hot, the second the alarm went off I shut down the port first and the alarm stopped. Stb was fine.
I'll be at the boat next week and put all this advice to use.
Maybe some crud got dislodged in the new imp install. Its only happened twice and months apart. Only at 500 rpms.

 

[shadow379]

Check the brand on the new impellers, I've seen this before with Sierra impellers and they look and feel identical to the genuine Yamaha part, however low RPM overheat conditions occur. Change them out with genuine Yamaha and the problem is solved. I don't know why, Sierra for the most part is well made but, just doesn't seem to cooperate with Yamaha too well. My 2 cents, hope it helps.

 

[seasick]

I didn't notice if the pee stream was strong. I checked at the dock before heading out and they were equal & normal.
The motor did not get hot, the second the alarm went off I shut down the port first and the alarm stopped. Stb was fine.
I'll be at the boat next week and put all this advice to use.
Maybe some crud got dislodged in the new imp install. Its only happened twice and months apart. Only at 500 rpms.

Crud is possible but I am suspicious of the idle revs. Normal idle speed is usually around 700 revs or so. At 500. you are probably not pumping a normal load of cooling water. Do both motors idle at 500?

 

[Curmudgeon]

Every motor I've owned had a weaker stream at idle compared to higher RPM, but not dribble weak, either. The one actual overheat I've experienced was in the yard due to low water volume from the hose. The other time I got a warning was to poor design of a flow sensor by Suzuki, the flow was actually normal.

If you received an overheat warning and the motor wasn't actually hot, I would surely check that out. The two usually go hand in hand ... :?

 

[ahill]

Seasick,
They were both idling in gear at 500 rpm.
Where is the idle adjustment on the OX 66's?
I'm glad you pointed that out, I forgot that OMC wanted idle at 650 in gear, I'm at 500 sometimes.

 

[Tucker]

Alan, my money's on the poppit valve (PRV). It's normally closed and allows the upper exhaust water chamber & heads to fill up when at low speeds. As the engine starts speeding up pressure from the pump & water temp makes the valve relieve (open). The tell tail has nothing to do with it. BUT the problem is the early design along with salt water deposits tend to make the valve stick in the rubber grommet. It's been replaced with a newer design that's impossible to stick open. I've replaced many of these valves, about $35 including the rubber grommet. Remove the ECU plastic cover (may need and impact screw driver), and unplug the 2-harness plugs at the bottom of the ECU. They're also secured with a simple bracketry. The biggest problem is dropping the new grommet in the exhaust cavity. I've done that twice and it's such a PIA to get out, I would recommend just leaving the one that's in there. It's not a tough job, leave the grommet in place and spray the whole area with vinegar, let it sit and rinse with water. The bolts are stainless and you'll need a10mm socket, universal and about a 9" extension. I use nothing but a 1/4" drive ratched on everything but the lower unit. Yup, snapped my share of bolts. Not a tough job just take your time.