Overheating?

Shallowminded · February 2018

Yamaha f40 runs fine at idle. From the time I put the boat in the water, and idled to the end of the no wake zone was 15 mins. I take off, got up and running @4500 rpms for a mile or so, overheat alarm goes off. The tell tale was flowing fine, water coming out wasn’t hot at all. Impeller was changed last year around May. Before I tear into this, I’m thinking thermostat? Any other thoughts?

larrywitt · February 2018

If the water was not hot or real warm the water may not be getting around the water jacket that surrounds the cylinder walls. Could be a number of reasons. Could be thermostat ,could be corrosion in passages. A laser thermometer will tell you where it is getting hot even at idle.
larrywitt

snookaffinity · February 2018

Thermostat would be the first thing I would check, but could be as stated above.

Slough · February 2018

Could be thermostat not opening properly (don't think it is stuck shut, would overheat at that long of an idle) or corrosion in passages. Sounds like not enough water flow and even with 1 year old impeller, that could be the problem. Laser thermometer can help.

Shallowminded · February 2018

Thanks fellas!

Barrell · February 2018

How old is the motor? Was it flushed religiously?

Shallowminded · February 2018

It’s a 2006 yammi 4stroke. To be honest no, if I fish on Saturday and know I’m going back out on Monday, I will spray the boat Doreen good but not flush the motor til after my Monday fishing trip.

larrywitt · February 2018

Fresh or salt water?

Bigguy · February 2018

put a digital thermo on the different parts of the engine but my guess is corrosion on the exhaust. Mine did the same thing years ago but the hand held thermo pointed to the exact place of heat

Dorado · February 2018

The T-stat is a moving part. For over 30 years when I run any of my boats (always in salt) I flush the motor, and have at the ready near the hose, a bottle of auto transmission fluid. After flushing for a minute or three, I shut off the water and quickly unscrew the hose and pour a tad of the **** fluid in it, then reattach and turn the water back on. It will exit the engine in a pink froth. Feel it, if you can. That slickness is also on your impeller and thermostat.

I once went six full years on a Johnson 150 T-stat when doing this, and decided it was due for an impeller..... I changed it, but the old one looked and worked just fine.

**** Catri taught me this trick.

Shallowminded · February 2018

Salt water, I replaced the t-stat went out yesterday and it ran just fine. Thanks everyone for the help!

Soda Popinski · February 2018

Dorado said:

The T-stat is a moving part. For over 30 years when I run any of my boats (always in salt) I flush the motor, and have at the ready near the hose, a bottle of auto transmission fluid. After flushing for a minute or three, I shut off the water and quickly unscrew the hose and pour a tad of the **** fluid in it, then reattach and turn the water back on. It will exit the engine in a pink froth. Feel it, if you can. That slickness is also on your impeller and thermostat.
I once went six full years on a Johnson 150 T-stat when doing this, and decided it was due for an impeller..... I changed it, but the old one looked and worked just fine.
**** Catri taught me this trick.

One of the many reasons I come on here. Definitely going to try this.

HannahBarge · April 2018

The overheating may be because of improper operation or problem in the motor. Sometimes it happens due to improper operation or there might be corrosion in it. It will be good to check it first if water is not hot. The thermostat will be the better option if you don't find the mentioned problem than you can go for it, but it will be better to check motor first.

Soda Popinski · July 2018

Having the exact same issue as the OP over the weekend. Thermostat and poppet valve are a year old, but i'm going to replace both this weekend.

Soda Popinski · July 2018

Replaced both t-stat/poppet valve 2 weeks ago, did a flush in a clean trash can with 10 gallons of vinegar first, then rinsed on the ear muffs then for a 45 minute ride on lake harris. No issues whatsoever.

tesilential · July 2018

Soda Popinski,

Did you notice a lot of crud come out when you did the vinegar flush? I overheated once at WOT a few weeks ago, so I changed my pressure control valve (poppit) and thermostat at the same time and started flushing with saltaway. It ran great for a couple weeks but now I'm getting a consistent overheat at about 5000 rpms. I'm thinking the saltaway may have broken down some stuff that got clogged further down the water passages.

I'm the first person I've heard of that started having overheating issues after doing the thermostat, poppit and saltaway.

The water isn't coming out the tell tale hot when I'm overheating now. It definitely was when I overheated a few weeks ago before doing the thermostat/etc.

Soda Popinski · July 2018

tesilential said:

Soda Popinski,

Did you notice a lot of crud come out when you did the vinegar flush? I overheated once at WOT a few weeks ago, so I changed my pressure control valve (poppit) and thermostat at the same time and started flushing with saltaway. It ran great for a couple weeks but now I'm getting a consistent overheat at about 5000 rpms. I'm thinking the saltaway may have broken down some stuff that got clogged further down the water passages.

I'm the first person I've heard of that started having overheating issues after doing the thermostat, poppit and saltaway.

The water isn't coming out the tell tale hot when I'm overheating now. It definitely was when I overheated a few weeks ago before doing the thermostat/etc.

That sounds more like a blockage in the water jacket.

When I did the vinegar flush the water had a greyish mirk to it but no hardcore sludge. I've used salt terminator before on flushes and ran it at boat ramps after salt water use so i don't think i ever had a multitude of gunk built up to speak of. When we took it out on lake harris I spent ample time putting it through it's paces to make sure the issue was solved. I have my boat listed on here and on CL for sale and I wouldn't sell it if it had any mechanical issues.

What I would do is another flush if I were you, might be a good idea to do a vinegar flush but turn the motor off and let it sit for say 30 minutes, then run it again, then sit 30 min then run again and then flush with fresh water.

Overheating?

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