overheat alarm

[rhenleyj]

My 2006 F250TXR overheat alarm goes off after a few minutes at low rpm but not at rpm over about 900. The temp gage reads normal, water flow stream from engine is fine and engine does not feel hot. If engine is cut off, alarm stops and does not come on for a minute or so when restarted at low rpm. This all started after a new impeller was installed.

[williamigriffith]

Engine alarm does not necessarily mean over heating

This answer was prompted by the question in the thread, but I took the opportunity to tell all re a recent experience.

I have had an F60 TLRA for several years, it is a 2003. Love the engine. A month ago I took it out in St. Helena Sound and about a mile from shore the alarm went off. Stopped it and sat. Restarted and alarm almost immediately went off. Saw a friend in the Power Squadron going home from a rescue and got towed in, very lucky.

I learned a few things from this experience as follows. Tell tale flow was weak, took off lower unit, water pump was pristine. Reinstalled LU. Disconnected line to tell tale (pee hole) and ran a string trimmer line through, much gunk. Lesson, always disconnect tell tale line before cleaning out, you are much less likely to get plugged up with the same debris (in this case the debris was like a plug, not loose pieces). BTW, the tell tale only tells you that the water pump is working, it is not part of the cooling system, and on my engine anyway, it lets out water at the bottom of the engine block before it cools anything. Next, removed cover of thermostat. In my case the thermostat is surrounded by a rubber collar, it can be pried gently out. Thermostat was stuck open. Put it in hot and cold water, nothing happened. Replaced thermostat with a new one. BTW, you can tell if your Tstat is stuck open if your engine immediately starts pumping out water when you put the muffs on the engine and run it. Normal operation would have the Tstat opening only after reaching operating temperature, but I never connected the dots. Lesson two, if your motor pumps water out the exhaust immediately when starting with muffs on, it is stuck open and needs to be replaced. Didn't see how the engine could overheat with a stuck open Tstat, but today I ran the engine for three hours and it purred like a kitten. Lesson three, apparently the Yamaha alarm goes off when the Tstat is not operating properly. I understand this better if it is stuck closed, obvious overheating, but my guess is that if after a while the engine does not reach a minimum temperature, the alarm goes off as well. Wish I had a temp gauge to know for sure that it was not hot when it went off. I also replaced the fuel filter, but I doubt that had anything to do with it, as it ran fine even with the alarm on.

Summary of things to check when alarm goes off and you expect it to be cooling related (not oil level, pressure, etc. etc.)

If tell tale is weak, take off cowl, remove tubing, push probe through hole, reconnect. If your motor has a hose fitting for flushing, this to will give you a strong tell tale stream without running your engine when the hose is connected. If the stream is good with the hose connected to the flush line, and less good when the muffs are on, you probably have a weak pump impeller.

If you get an alarm and the tell tale is strong, check Tstat. Very easy to do. If closed, put in boiling water and see if it opens, if it doesn't it is bad. If it is open at room temperature, it is stuck open and bad. If your motor pumps water out the exhaust immediately when starting up, thermostat is for sure bad.

If your alarm goes off the engine may not be overheating at all, it may be something that happens when the Tstat sticks in the open position. Any way, these are just my thoughts, I am not a Yamaha mechanic but I am mechanically inclined. Hope this helps, it would have helped me.

[99yam40]

to OP check/change the PRV

To the other poster Stat does not have to open for water to flow out of Tell Tail

[williamigriffith]

Don't believe I said anything about tell tale re Tstat

The tell tale is completely unrelated to the Tstat, other than the fact that the tell tale flow rate could change a bit in strength whether Tstat was open or closed. If I somehow implied that, I did not mean to.

[rodbolt17]

alarm wont trigger for over cooling.
a stuck open T-stat wont trigger overheat.
some later model EFI motors will throw a code for overcooling but not an audible alarm.

on the F250, if you get an overtemp with no visual indicates its typically the head got hot and the block did not.

only good way to verify that is by watching the laptop and look at the temp switch condition, on or off.

the F250 has 1 thermosensor and two thermo switches.

[Joebeeney]

Yamaha 25hp 1992 2 stroke over heating

Here is what I've done so far....
New Impeller and bowl. Cleaned everything around impeller. Never been in salt water. I changed thermostat and blew out the water system from the outlet on back of motor with little to no resistance with an air hose. Motor pees very well but still over heats in neutral at idle after a few minutes.
Note... Old impeller was completely disintigrated when i bought motor and i got all the pieces out of the lower end and water pump area. When i hooked air hose and back flushed the system air came out of exhaust and lower end screens for water intake.

Any ideas.... I'm stumped. Is there any way the head or power head could be clogged if its pumping really well. I also wanted to ad that the water coming out of pee hole is very hot. Burnt my hand.
Motor compression tests at 110 psi as well in both cylinders.

[TownsendsFJR1300]

Someone recently had an anoid (sp?) break off a small piece and get in the cooling passages causing overheat issues.

I'd be leaning towards a piece of impellor doing the same, getting jambed up in a cooling jacket.

As I re-call, Rodbolt mentioned in that thread a way to check clean it W/O pulling the heads (might be wrong).

A lazer temp gun pointed at each head, in the same area, will likely show MUCH dfferent temps between the heads when its acting up. (narrowing down the area, should a head need to be pulled).

Good luck..

[rodbolt17]

well now we have a thread hopper.
the F250 and the 25 don't share much.

[boscoe99]

well now we have a thread hopper.
the F250 and the 25 don't share much.

Well they are both Yamaha's. Both are painted gray.

[TownsendsFJR1300]

They don't both have coolant passages in the powerhead? Hummmm..

Broken impellor pieces can't be pumped into the powerhead and cause obstructions??? (same as the anoid?)..

Sure as heck can..

[99yam40]

he posted on an old thread about a different motor,
he did open his own thread properly so let this one drop

[justincblades]

Try Pressure relief valve. Its $90 and easy to get to. Mine didn't run hot unless it was at an idle. Replaced, no problem since.

[Nautical]

Good at 900 rpms but alarm goes off at 600 RPMs.. Not a whole lot of difference there. I would also look at the temp alarm switch /sensor ??