98 Johnson 225 Temp Alarm / Overheating

[Bergertime]

Hello all... I have a new to me 97 Osprey 245 with a 98 225 Johnson on it.  Went out on Sunday and the temp alarm started going off after I pulled up my anchor for my return back to the ramp after being anchored for some time.  I idled for a while and the alarm and light went off (stopped) but my motor would not go above 3K rpms  (prob safe mode). Some of the research I have done points to the T-Stats.  I have ordered replacements for both with gaskets but I was wondering if I am headed in the right direction based on some of the facts below.

1) Boat would not allow RPMs above 3K in gear or neutral on Sunday when returning (ran fine on the way out with no issues)

2) Impeller was replaced 3 weeks ago and pee stream is strong

3) Boat did not like running on muffs out of the water after impeller change, temp alarm sounded when I used them a few weeks ago but when I put hose to the upper washdown port (PO never used muffs) the alarm stopped.  I have been using the upper hose connection since (5-7 times) and have never had the alarm sound.

4) When I got back to my house and flushed the motor Sunday using the upper washdown port the temp alarm never sounded even after running for 7-8 minutes.

4) The water coming out of the back of the prop and off lower unit is fairly warm to the touch but not extremely hot after running for 7-8 minutes.  I have not had a chance to check the vents above the cavitation plate for outflow after warm-up, just learned about that yesterday.

5) The temp alarm has sounded before (a couple times) when idling in the water (at ramp and beach) but always stopped after a couple min or when I started to move. I have never had the RPM limit issue happen b/f and I have used the boat 7-8 times since I purchased it last month.

Any insight would be greatly appreciated.  Thanks in advance.


BB

[Capt. Bill]

Sounds more electrical to me.  If you have good flow out the back and it isn't steaming I'd say sending units or the brain on the dash. (Thats the unit  with the lights and alarm) It may be included in your TACH.

[Blue Agave]

Did you have the same issues prior to changing the impeller?  If not maybe an issue with the install or replacement impeller.

[Bergertime]

I had the impeller changed right after I purchased the boat along with the gear lube, starter and some other routine maintenance so I did not get a chance to really see the b/f and after prior to the impeller change.  I did operate the boat for the sea trial for 30 min or so and there was no sign of temp issues.  

I guess I will start with the t-stats since they are on the way via USPS and work from there.  Once I change them I can watch for the triggered outflow via the cavitation vents when the engine warms up.   In my research I have heard that the t-stats are responsible for triggering the the alarm and light, failure (not opening) will cause this issue.  Can anyone confirm this regarding a 98 Johnson 225?.  In addition, I will buy some muffs and test the cooling from there since that will more closely simulate the engine being submerged in water.  I am new to all this so any further suggestions on my approach or focus would be appreciated.

BB

[wingtime]

Changing the T-stats is good idea anyways on a boat that is new to you.  If the does not solve it then the impellers is installed wrong or the water pipe was misaligned or something.

[Bergertime]

Thanks all..  Hoping the t-stats come is so I can work on her Sunday.  Will post follow-up after I take my first swing at this problem.

BB

[Capt. Bob]

I'm sure the real pistonheads will respond but I'd check flow from the cav plate vents. Use the muffs. Water should not flow upon start up but after just a short time, you will see the water exit the vents, slowly at first then stronger as the stats fully open. This is SOP pretty much and a fair indicator of working stats.

I always thought that the upper hose fitting was for flushing without running.  Think boat at a saltwater mooring. Someone smarter will confirm/ deny.

Overheating at idle is often (but not always) stat/impeller related.

Good luck.

[fitz73222]

I'm sure the real pistonheads will respond but I'd check flow from the cav plate vents. Use the muffs. Water should not flow upon start up but after just a short time, you will see the water exit the vents, slowly at first then stronger as the stats fully open. This is SOP pretty much and a fair indicator of working stats.

I always thought that the upper hose fitting was for flushing without running.  Think boat at a saltwater mooring. Someone smarter will confirm/ deny.

Overheating at idle is often (but not always) stat/impeller related.

Good luck.

As wing suggests the thermostats are a good place too start and should be considered a maintenance baseline along with the impeller. So if she still gives a hot signal we should look at the overheat sensor or warning module. The best way to verify overheat condition is place your hand on the cylinder heads and see if she is really that hot. You cannot hold your hand on 160 degrees without burning it but you can handle 120-140 degrees briefly to understand the running temp.Additionally, the upper flush adapter is for flushing the engine without it running. So the muffs are the way to go. I like muffs because the engine will warm up and when the thermostat opens, it will flush out the thermostats along with the rest of the cooling system at operating temperature.

[Bergertime]

Thanks guys for the continued support and insight.  I will be working on her on Sunday following your advice starting with the stats and running with muffs.  I have a boat ramp 15 min from my house so I will take her out for a spin to validate my efforts good or bad.  

Although I'm a newbie at this I have a gut feeling or wishful thinking that it's the stats.  Based on the PO's own statements and watching him at the high and dry motor rinses were done exclusively via the hose port and I duplicated the same practice.  Anyway, I will begin using muffs moving forward.

MM- If the new stats fail to resolve the problem do you mind coaching me through the next steps mentioned (over heat sensor / warning module)  In addition I may have the impeller inspected.  Based on a couple non-related issues I have had I have some cause to question the quality of work of the mechanic that serviced my lower unit.  

Thanks again!

BB

[Capt. Bob]

I will be working on her on Sunday following your advice starting with the stats and running with muffs.  
BB

While I'm a firm believer in regular stat replacement, I would suggest that you run the engine on the muffs first before digging into the motor. Only takes a few minutes and if the stats are sticking/clogged, you will see the flow or lack of, through the vents. This can then be used for future observations and is IMHO a good learning tool.

That stated, even if you see flow I would, as suggested by others, change the stats AND inspect the impeller and its connections. I think all will agree that when you take ownership of a "new to you" used motor, replacing these cooling components is a good first place to start.

Good luck.

[Bergertime]

Gentlemen,

My t-stats came in last night so I think I’m ready for the replacement.  However, I have one question.  When I replace the gasket for the cover is there anything that I need to coat the gasket with or does it just go in dry? My guy tells me something will likely be needed there and I want to make sure that I have everything on hand to complete the replacement right.   Thoughts?

BB

[kraw2]

On the aluminum housing you can use gasket sealing compound or a little high temp gasket compound. Not much...

[saltfly]

That motor has two temp. sensors, one  in each power head. You can see the wires from them coming out of the top of each head. If one or both of them go bad, you motor will kick in the rmp limiter and sound the alarm. To check them. Unhook both sensors. there is a single wire connector under  sliding rubber covers. Start and run your motor. If the alarm doesn’t go off and runs above 3000. Then one or both of them are bad and need to replace. You can check to see if one is bad, by hooking one and running the motor. If the motor runs find then that one is good and the other is bad. You can again check it, by hooking it back up and running your motor, and if the problem is their that proves it was bad. It would be worth trying just to be sure they are not your problem. those sensors can go bad over time with out having a real over heating problem.

[dburr]

BB
It sounds like the water pump has been damaged, not cooked, and is providing the minimum cooling it can.  Fitz is correct about the flush...  I have not been able to find anywhere that is says it's ok to RUN the (a) motor on a power head flush.. (My Yam OX66 150 book uses big bold black letters that says the flush is not to be used to run the engine, that is a muffs only operation. )  So why are you getting cooling water?  It stands to reason that there will be some water that gets down the uptake tube while you flush and somehow it was keeping the water pump lubricated and you got lucky.  I have a sneaking suspicion that you‘re not getting the cooling flow you expect.  Without the OMC diagram in front of me I cannot say with authority where the tell tail hose is in the system.  I have a Merc of that vintage and the tell tail is at the bottom of the power head near the INLET of the cooling water to the head and the Tstat is nearer to the top of the head.  All it tells me is that water is going somewhere, but where is not guaranteed.  

As the boys have said, run the engine using the raw water pickup to see if the pump is sick and to check if the tstats are working..  Best bet would be to use a cut down barrel or garbage can that has the rim line with the up vent plate and run a hose in and keep running the hose in and running while the engine runs.  An alternate solution would be to drill some 1 inch drain holes at the correct height so you don't destroy a perfectly good garbage can (and avoid an educational realignment from the Big Boss   )...  If you don't run the hose then the water heats up and could give you a false trip of the overtemp alarm.  There will be plenty of water in the barrel for the pump to pick up and you can still check the vent holes above the vent plate for tstat operation like CB says..  If all this effort yields no definitive result, get a shop manual or a Seloc book and follow the advice that Fitz, Wing and Salt have given on the electrics..  Let us know what you find!  Happy hunting!

[flounderpounder225]

Just adding my .02 cents.  Everything that has been suggested is exactly what I would do, but one thing I did not see in the discussion is what type of flusher you are using.  The bigger Motors like water, my 250 Yammi will over heat on the hose if I am using a single sided hose feed flusher, she needs water from both input screens, I use this one from west, http://www.westmarine.com/webapp/wcs/st ... FtnOaN5mSM

There is a sea sense model out there for less but the rigid horseshoe feed (the wishbone looking thing) is made of plastic and I hade two of them break from age, the west one is made of metal.  IMO this is a good investment for max cooling water to the engine.