Yamaha V4 115 BETO overheat thermostat or temp sensor

[stop8stop8]

Hi Folks,

I have a 115 V4 BETO from 1995.

We went out yesterday for the first time this year and she started first time with no problem.
The impeller was changed last year so really strong tell tale jet.
I topped off the oil tank and left the marina.

After 5 minutes or so of running the alarm went off and stayed on and she went into limp home mode.
I stopped and checked the oil tank as I thought the float may have been stuck but all looked ok but the alarm remained on.

After a 30 minute break / swim we set off again and the alarm came back on after 5 minutes or so.

When we got back home I decided to pull the thermostats and test them in a pan of water on the stove. Both thermostats opened fully at the same time as the water got hot.
(I was hoping one was not working and that it was an easy fix)

If its not the thermostats could one of the two heat sensors (or both) on either head be causing this overheat alarm if they are beginning to fail.?

Whats the best way to test that theory,? Simply removing or disconnecting them one at a time and running the engine to see if the alarm comes on.?

Will it be safe to do so now I know the thermostats are working ok.?

Thanks in advance
Stop8

[TownsendsFJR1300]

Salt water use?

How much corrosion inside the engine?

Does the engine go into limp mode at slower RPMs (say under 4,000 RPM's) or run ok?

Might want to check the "water relief valve" pictured below (part #43). If leaking, water will not stay up in the block (it releases excess water pressure)

https://www.boats.net/catalog/yamaha...nder-crankcase


And NO, do not run it in the condition it's in (ignoring the alarm). If there's major corrosion/build up in the head, there will be little to NO water flow.
Of course this can cause SERIOUS damage..




Capture.JPG

[99yam40]

PRV normally stuck open will cause an overheat at low RPMs, water pump cannot keep the block filled.
higher RPMs the water pump will fill the block just fine because it pumps so much more water at higher RPMs.
what RPM were you running both times the alarm sounded?

never hurts to inspect the pump. it can come apart quickly some times

[stop8stop8]

Hi again,

Thanks for your answers and sorry for the late response but I decided to take the boat out again and run a few tests in order to answer your questions.

So, its salt water usage and there is some corrosion inside the thermostat housings but not enough to be a concern yet.
I checked the water relief valve last night and it was clean, no blockages or leaks to note.

Today the engine started first time and a strong tell tale, warm to the touch.

We ran on the plane but under 4000 rpms for over 20 minutes and no alarms. Once we arrived at our destination I opened her up to full throttle and the alarm came on after about 90 seconds.
We anchored up and after 5 mins I turned the key and no alarm.
After an hour or so we set off back to the marina, again on the plane and rpms under 4000.

Once almost back at the marina, ran her at WOT and again after 1.5 - 2 minutes the alarm came on and we slowed down and came back in to port.
The alarm went stopped sounding again after about 5 minutes when waiting alongside the slipway.

I am thinking I should remove the heat sensors and test the resistance with a voltmeter when they are in a pan of warm water on the stove. Whats your thoughts on that.?

I also saw a post saying to remove the leg and thermostat and run a hose pipe with good pressure from down inside the thermostat housing to back flush the system and force any crud back out of the down pipe in the leg that may be blocking water flow

Any further thoughts please.?
Thx

[gtreanto]

Hi again,

Thanks for your answers and sorry for the late response but I decided to take the boat out again and run a few tests in order to answer your questions.

So, its salt water usage and there is some corrosion inside the thermostat housings but not enough to be a concern yet.
I checked the water relief valve last night and it was clean, no blockages or leaks to note.

Today the engine started first time and a strong tell tale, warm to the touch.

We ran on the plane but under 4000 rpms for over 20 minutes and no alarms. Once we arrived at our destination I opened her up to full throttle and the alarm came on after about 90 seconds.
We anchored up and after 5 mins I turned the key and no alarm.
After an hour or so we set off back to the marina, again on the plane and rpms under 4000.

Once almost back at the marina, ran her at WOT and again after 1.5 - 2 minutes the alarm came on and we slowed down and came back in to port.
The alarm went stopped sounding again after about 5 minutes when waiting alongside the slipway.

I am thinking I should remove the heat sensors and test the resistance with a voltmeter when they are in a pan of warm water on the stove. Whats your thoughts on that.?

I also saw a post saying to remove the leg and thermostat and run a hose pipe with good pressure from down inside the thermostat housing to back flush the system and force any crud back out of the down pipe in the leg that may be blocking water flow

Any further thoughts please.?
Thx

When was the last time you replaced the waterpump?

[TownsendsFJR1300]

Sounds like salt water corrosion build up in the heads.

Some water makes it thru the heads but at the higher RPMs, NOT ENOUGH water flows thru, setting off the alarm..

The fix is R&R the head(s), clean all the water jackets around the block and in the head...


You can do a search here for chemical flushing which is sometimes, somewhat effective. Depends on how bad the blockage is..


My neighbor had the exact same issue for his V6 200. Pulled the heads, NASTY with salt water corrosion/build up. Cleaned heads and block, ran like new..


.

[ausnoelm]

Pretty common Yamaha symptom, time to remove the heads and clean out the water passages, broken bolts might prove challenging. There is no "easy fix" running hoses back down, flushing with acid/vinegar/salt away sometimes helps, but rarely, it's time to fix it properly.

[ausnoelm]

Just a tip, there is no "limp home mode" the motor is telling you to stop, you don't take note of the alarm, it goes into RPM reduction to tell you it's dying, "limping home" without oil, or an over heating motor will kill it stone dead.

[99yam40]

recirculating Ridlyme marine scale remover has had good reports in the past.

I have used citric acid before, recirculate it thru the system with a pump.
drop lower unit and hook hose to up pipe and catch all of the solution and keep it pumping thru.

I have also used a water hose hooked to up tube,, remove stats and turn water on full blast, to flush out cooling system.
some compressed air injected into the water hose from time to time helps move things around and come out.
at least it helps the loose sand and flakes of scale that build up in the lower passages get pushed out

[ausnoelm]

The issue is really simple yet complicated, the build up is not just salt, if it was, warm water will dissolve it in a second, the build up is a mixture of all sorts of minerals, solidified by heat, nothing will dissolve it (well, nothing that won't eat the engine too) flushing buys some time at best, it can remove enough build up to prevent the alarm going off, but, it's still running hot and life shortened considerably, removing anything to gain access and mechanically removing the build up is the only "fix" everything else is a patch.

[99yam40]

The issue is really simple yet complicated, the build up is not just salt, if it was, warm water will dissolve it in a second, the build up is a mixture of all sorts of minerals, solidified by heat, nothing will dissolve it (well, nothing that won't eat the engine too) flushing buys some time at best, it can remove enough build up to prevent the alarm going off, but, it's still running hot and life shortened considerably, removing anything to gain access and mechanically removing the build up is the only "fix" everything else is a patch.

true, but busting a bunch of bolts off is a problem you try to ovoid at all costs

Ridlyme is a descaler meant to dissolve mineral deposits in even large marine heat exchangers.
it will remove barnacles and zebra mussels too
as long as you can get it to the deposits it can remove them from what I have read. and people have had good luck on outboards with it

[panasonic]

I am with everyone else on this, most likely blocked water passages. But I am also for checking your alarm system temperature sensors for proper operation before doing anything else.

Do you have a Yamaha manual for your engine? It will have the test procedures in it.

[stop8stop8]

Thanks all for the comments folks, really helpful.
I have ordered some new gaskets so I can do the heads / water passages as suggested.

In the mean time I dropped the leg just to check all ok with the impeller etc.
On the top of the impeller housing just where it connects to the up pipe was a large piece of black rubber which is most likely from the old impeller.
I removed this piece and then back flushed with high pressure water from the thermostat housing to force any other pieces that may be in there back out.
I then put everything back together, ready to test again this week.

I should say that when I bought the engine at the start of last year the old impeller was the worst I had ever seen (pic attached) and a lot of the rubber pieces got up inside the cooling system and clogged in the thermostats and the water relief valve. I had to strip and remove all the bits before even going out for the first trip last year and even then had to repeat this process a second time after going out once or twice.

We went out over 15 times in the end last year without any subsequent problems but it looks like one final piece has moved inside the passages over the winter and possibly caused a blockage.

I will go out this week to test again to see if this has resolved the issue and if not I will remove the heads and clean the water passages as suggested.

Thanks again all.

[panasonic]

"I should say that when I bought the engine at the start of last year the old impeller was the worst I had ever seen"

Why would you not mention that in you very first post?

[99yam40]

"I should say that when I bought the engine at the start of last year the old impeller was the worst I had ever seen"

Why would you not mention that in you very first post?

I agree, why have everyone guessing .


and I am trying to figure out how that piece got on top of the water pump housing