High RPM overheating.

[Sheff 69]

2002 Yamaha 90 TLRA

While I've had the boat about a year, I've been refreshing the internals.
New fuel lines, pump, filters etc.. New wiring from scratch. Just about everything I could think of.

Today, on the last day I could put the boat on the water, before I have to leave for the summer, I got a problem.

The motor fires up just fine. Idles well, although a couple of hundred degrees low. Around 650 rpm. I can fix that.
Set off from the marina at around 2500 rpm, ran for 10-15 minutes then hit the unlimited speed zone.
Powered up to full throttle and got to 5500 rpm felt wonderful, then after about 10 minutes, the motor alarmed,and de-powered.

I shut off the engine, sat for 10 minutes, then it fired right back up and ran great for about 3 minutes at 4000 rpm when it shut back down again.

Sat again for about 10 minutes, and then it fired back up, and it ran great for 20 minute at idle, then it ran great for over 20 minutes at 2000 rpm, then finally ran for 30 minutes at 2500 rpm,
no problems.

Obviously I have a cooling problem.

Anyone have any thoughts on where to start?

Not urgent, but like to think things through before I start tearing things apart.

John

[robert graham]

Drop lower unit and inspect/replace water pump, wear plate, pump housing, water tube, grommets, etc.....remove and check/clean/replace thermostat and pressure control valve....if this was/is a saltwater motor then check passageways for salt/mineral deposits....if plugged up then consider a chemical cleaning with Saltaway or similar product.

[99yam40]

2002 Yamaha 90 TLRA

The motor fires up just fine. Idles well, although a couple of hundred degrees low

John

Degrees deal with timing or temerature

How has this motor run in the past?
have you done anything with the cooling system?

[Sheff 69]

Drop lower unit and inspect/replace water pump, wear plate, pump housing, water tube, grommets, etc.....remove and check/clean/replace thermostat and pressure control valve....if this was/is a saltwater motor then check passageways for salt/mineral deposits....if plugged up then consider a chemical cleaning with Saltaway or similar product.

When I got the boat, the first thing I did was to replace the water pump, just about everything. The only thing I saved was the metal housing and the bolts.
The tell tale stream is very strong at all rpms. I didn't change the water tube grommets, thanks for that idea. I have 15 running hours on the rebuild.
I will change the T-Stat and pressure control valve (when I find it). Motor has always run in salt water. Do I have to pull the head to check the passageways?
I will try the Saltaway. Thanks for your input.

John

[Sheff 69]

Degrees deal with timing or temerature

How has this motor run in the past?
have you done anything with the cooling system?

I don't know where that came from, I really meant rpm's. Sorry.

As replied to Robert Graham, the only thing I have done is replace the water pump.
I don't know how the motor has been run in the past.
For what it is worth, when I bought the boat, the PO had a mechanic check the compression in the cylinders and he reported 121 psi in two cylinders and 119 in the third, so I was hoping it was reasonably sound.
Up to now, I haven't been able to run the motor hard, so never knew I had an overheat problem.
After the summer, I intend to do a full service on the motor, when I'll look inside from the T-Stat.
Hoping not to have to pull the head, but if I do, it doesn't look that hard. At least there are no valves and timing to deal with.

Thanks
John

[ausnoelm]

Common problem, only solution is remove the heads and clean the crap out, taking care not to break any bolts.

[99yam40]

when you pull the stat you can get an idea of how bad the passages are.

do a search on Rydlym Marine descaler, I have read some good results from using it.
last resort is taking motor apart to clean it

[ausnoelm]

Lots of people try vinegar and proprietary salt removing "stuff" but none work properly, once the passages are choked up, mechanically digging it out is the only option, some salt dissolving products are OK as a preventative, but as a cure...nope, the problem is, it's not only salt you are trying to dissolve, it's all sorts of minerals, hardened by age and heat, nothing except maybe something that will eat your motor too will work.

[TownsendsFJR1300]

Lots of people try vinegar and proprietary salt removing "stuff" but none work properly, once the passages are choked up, mechanically digging it out is the only option, some salt dissolving products are OK as a preventative, but as a cure...nope, the problem is, it's not only salt you are trying to dissolve, it's all sorts of minerals, hardened by age and heat, nothing except maybe something that will eat your motor too will work.

+1 ^^^.

Sounds like the head and water passages (in the block) are clogged up with salt. Your cooling system can currently keep it cool at lower RPMs.

At higher RPMs, there's not enough flow and too much heat causing the over heat....

[Sheff 69]

when you pull the stat you can get an idea of how bad the passages are.

do a search on Rydlym Marine descaler, I have read some good results from using it.
last resort is taking motor apart to clean it

Thanks, I'll try that before I pull the head. One last attempt before I bite the bullet. I guess I have a project now for when I get back beginning of September.

One last question, can I clean the block in-situ, while still connected to the lower unit, or do I have to pull the powerhead off to clean it properly?

John

[pstephens46]

No you don’t have to pull the power head. At least remove and inspect thermostat first. That’s easy and may indicate what you are up against.

[99yam40]

Thanks, I'll try that before I pull the head. One last attempt before I bite the bullet. I guess I have a project now for when I get back beginning of September.

One last question, can I clean the block in-situ, while still connected to the lower unit, or do I have to pull the powerhead off to clean it properly?

John

like said pull and see if stat is bad or restricting flow.
but you can drop lower unit ,hook up hose to pipe, and recirculate cleaner.

you will get an idea when you read up on it

[DennisG01]

If I read correctly, you did NOT replace the metal impeller housing. I'd look at that, too. ANY little bit of scoring can cause issues. It's also possible that you sucked up sand or grit and that scored the new wear plate.

[TownsendsFJR1300]

I couldn't find the prior threads with the other posts (apparently went away with the upgraded operating system here) but

here's some reading for ya. As most engines nowadays have a flush port on the power head, I don't see why you would have to remove the impeller.
Removing the thermostat is a "should do" for the most effective treatment.

http://www.rydlymemarine.com/assets/...structions.pdf

[Sheff 69]

If I read correctly, you did NOT replace the metal impeller housing. I'd look at that, too. ANY little bit of scoring can cause issues. It's also possible that you sucked up sand or grit and that scored the new wear plate.

That's correct. When I bought the boat the P.O. said he had just changed the water pump, gave me the receipts to prove it.
Just being cautious, I pulled it apart and saw that the housing had been attacked by a pair of Channelocks, so I replaced the impeller and the housing. The metal impeller casing was perfect, no scratches, scoring or color changes, so I reused it. Since I have grounded a few times in sand since I got it, I do intend to pull the pump apart again in Sept.
Thanks for the comment.