'94 Force 120 still overheats even with new water pump

[ggundersen3]

The overheat alarm sounded twice a few weeks ago after slowing down to low RPM after running high RPM (2/3-3/4 throttle). I took it to local dealer and they said it was the water pump that was bad so I paid them to replace it and they stated they tested the motor afterwards and all was OK. This weekend I out on a local lake and it seemed fine until the same situation took place, I was running 3/4 throttle for quite some time, then finally slowed down to "no wake speed"and after running slow for 10 minutes, the overheat alarm sounded again! It happened twice on Saturday. Obviously the water pump wasn't causing this. What could it be causing this? This is exactly what it was doing before installing the new water pump. The new water pump made no difference. It's something else!

 

[Oregonbayliner]

Thermostat? seems like a strange time for it to overheat unless maybe theres pieces of water pump blocking water flow through?

 

[jerryjerry05]

The dealer probably did the job right, they just didn't do a complete job

In the event of an overheat, they should have check the thermostat too.
They should have also tested the motor with a heat gun after installing the impeller.

You can check the tthermo yourself.

Also did the dealer give you the old parts?
Check the old impeller for missing vanes?

 

[ggundersen3]

Thanks for the info. Its back at the dealer this morning do we'll see. And no, they did not give me the old parts.

 

[ggundersen3]

So here's what the dealer came up with....."The exhaust cover gaskets have compressed over the years and caused exhaust to leak into the cooling water." Bolts for the exhaust cover were loose.They tightened all the bolts and the motor ran cooler.
OK I need your opinions if this diagnoses they came up with makes sense? Tell me what you think.

 

[Jiggz]

The diagnosis is possible but the question remains, "Why only when going slow, that it overheats?" and not at high speed? Personally, I would take a look at the t-stat to make sure there is no blockage and at the same time check it using a thermometer and a pot of water over the stove.

 

[ggundersen3]

They stated they did check the thermostat and its working correctly

 

[kbh121956]

Get a harbor freight Thermo temp gun, They are cheap. uses a laser light and check your temps when going slow. Awesome tool to own and easy to use.

 

[jerryjerry05]

It sounds like the "dealer" is in way over his head???

.."The exhaust cover gaskets have compressed over the years and caused exhaust to leak into the cooling water."
WOW!!!!! if you can't dazzle them with brilliance??
Baffle them with Bull S&^%%

The cooling water and exhaust is supposed to mix.
If there was a problem?? that problem would have resulted in water in the lower cylinders.

If they really did check the thermo?? then it will be real easy to remove and test.

Always ask for the old parts.
I always give them a bag with the old stuff and they can do with it what they want.

Take the thermo out and test it?
Check the area behind the thermo for crud build up.

It's possible the cooling passages have crud build up?​

 

[Jiggz]

They stated they did check the thermostat and its working correctly

When you get the motor back and ready to go into the water. Remove the t-stat. It's really easy just make sure you preserve the gasket and take note of the orientation. Now do the test runs. If there is no overheating. Re-install the t-stat again and then let us know if there's still overheating.

 

[ggundersen3]

Still struggling with this. Running it with no thermostat as Jiggz suggested is what I'm trying next. Since my last post I took it too a different dealer who is knowledgeable on Force and he checked the thermostat and found it had gunk/debris had collected around and on the thermostat. He thoroughly cleaned it all out, then tested the thermostat to find it working good. I took the boat out on the lake yesterday and yes, after running between 1/2 to 3/4 throttle the overheat alarm eventually sounded again.Crap! When it sounded I removed the motor cover and checked the exhaust cover on the side and it was red hot! Is that right? I thought the cooling water travels through there before going through the engine hence it should be cool. Also, the water being discharged from the discharge holes (it was discharging alot of water as it should) was blazing hot. So Im still searching for a solution. Remove the thermostat and run it on the lake and see what happens I guess is next. Correct?

 

[jerryjerry05]

Yes, take it out and see?

It sounds like it might have the blades from the old impeller stuck up in the passages?
Ask the guy who changed the impeller if it came out in 1 piece? or was missing the vanes?

 

[Jiggz]

Just to give you an idea on the cooling water flow . . . the pics maybe for a four cylinder motor, but the principle is basically the same.

 

[kbh121956]

Jiggz, Thank you for the photo. I always wondered how the flow works on these force outboards. Could his trouble be with the water pressure relief valve? Or, is that a valve that just removes too much cooling water? Could that valve be stuck open? I'm still learning.

 

[Jiggz]

The problem is not that complicated but access to the exhaust plate cover, as much as possible is avoided since it is really a PITA because 50% of the time, you will break bolts due to heat and sea water exposure. So instead of trying to pinpoint the source of the problem, do a process of elimination.

So far, you have eliminated the impeller after it was replaced. The next step should be to eliminate the t-stat by removing, replacing the cover and ran it. If the problem persists, then the next option is to back flush the cooling system or open and inspect the exhaust plate cover. AGAIN YOU WANT TO AVOID DOING THIS UNLESS IT IS A LAST RESORT.

Another option is to remove the head (saving the gasket) and inspect the cooling ports. Again this is also a very tedious action since it involves torquing the bolts when you replace the head.

 

[jerryjerry05]

No pressure relief on he 94/120

You said the thermo had corrosion/gunk?
Like Jiggz suggests remove the head and check the passages.

If you run a lot in shallow water or find sandbars a lot, you might be full of sand?
The pic: that motor took over an hour to clean the passages that were full of sediments.

 

[ggundersen3]

Nothing resolved yet here. Removing thermostat and replacing cap/cover and running it without it is next. I did waste a week by taking it to repair shop #3 that came highly recomended and having it sit there for 6 days only to have them call saying they wont work on it because my trim and tilt doesnt work and thus they cant get into their test tank. (How about lifting it like I do when I launch? Huh?Sound like BS). I'll advise the results after running it with no thermostat. BTW, running it with no thermostat doesnt hurt anything does it?

 

[ggundersen3]

BTW JIGGS... Explain how to backflush the cooling system.

 

[Jiggz]

Backflushing requires feeding pressured water into the t-stat housing to ran back to the cooling water tube in the LU. The easier thing to do instead is to flush the system by connecting a garden hose with proper adapter to the cooling tube in the LU. Using a flashlight, inspect the cooling tube to make sure it is not broken or cracked or sealed damaged leaking water back into the lower leg. Which would indicate a good flow of water but really is just leaking from the feed cooling tube.

Remove the t-stat cover and you should see a good amount of water pouring out of the t-stat housing. This will ran water into the motor but it is fresh water so it will not hurt anything.

The other option is to remove the plug on the t-stat housing and then install a nipple and hose to direct water off the motor. Always start with low pressure water. If you do not see water or good amount of water coming off the t-stat housing, there is a very good chance there is an obstruction in the cooling ports or there is a leak in the cooling tube not allowing enough water to go through the entire cooling ports.

The next step is to remove the head and inspect the cooling ports. If all is good, then the next step is to remove the exhaust plate, to open and inspect.

You mentioned there is good flow of water when running it, so I would suspect without the t-stat the overheating problem would go away. Unless, such good amount of cooling water is really just leaking from the cooling tube in the LU. And no, it would not hurt anything not to have the t-stat especially if you're running the boat down south on warm waters.

 

[jerryjerry05]

Running with no thermo: they run best when ran at a certain temp range.
The fuel economy and performance is better at that temp.
It won't hurt a thing running without one.