Running engine on flush hose

[Hookster57]

I had my marina mechanics install a port lower unit (got it at hardcore marine for $1500). The Marlin was on the rack and when I asked him if he sea trailed it he said he ran the engine on the flush hose to check the job. The Yamaha 250 manual says to never run the engine off the hose, not enough water to cool the engine. When I took the boat out for the first time the engine overheat warning came on. I shut down the engine for a while then started it back up and it's run fine since then. Question: do you think any damage occurred during his procedure?

Thanx.

 

[magicalbill]

Interesting. I would consider it a red flag no-no if he ran water for testing thru the flush hose as opposed to the muffs that you attach to the lower unit.

Your speaking of the threaded flush attachment on the side of the cowling for a garden hose, right? I use that to flush my engines dockside to rinse the salt out, but I would never start one up using that as the water source.

 

[magicalbill]

I just saw I didn't answer the question. If it was me, I would fret over it and get it checked by a qualified Yamaha guy for peace of mind. Hopefully some of the folks here will give a more educated answer.

 

[Hookster57]

I'm not sure if he used the muffs or just the hose flush. This guy is a certified Yamaha guy ....( :uhm

 

[magicalbill]

If he used the muffs that attach to the lower unit, that is normal procedure for running an engine while the boat is drydocked.
Surely a certified Yamaha guy would do that as opposed to the side hose attachment.

In either case, I would tell him about the warning buzzer or lite that came on. The fact that it didn't come on again and the possibility that the mechanic used the muffs on the lower unit is good news to me.

 

[Doc Stressor]

I got this from a certified Yamaha mechanic at Homosassa Marine:

Yamaha used to say that their engines could be run when using the flush attachment rather than earmuffs. But they ran into problems with people running their engines at high rpm. There were instances of overheating and also damage to the impellers. So now they say not to run the engine from the hose attachment.

The factory trained guys will still run them off the hose attachment, but they are careful to only do it for a short time and never over idle speed.

It's possible that you had a temporary air blockage in the upper part of the cooling jacket that triggered the alarm. As long as the problem doesn't persist, I wouldn't worry about any damage. The alarm goes off at just below 200 degrees. Car engines normally run higher than that, so no damage should have occurred as long as you shut the engine down.

 

[Capt Bill]

I would be concerned that the impeller has been overheated, which couple melt and partially restrict the water passageway. For flushing, I made up a Y hose adapter for flushing. This allows me to flush thru the muffs and engine flush hose at the same time. The local Yamaha lead tech told me this is how they do it at their dealership.

 

[GulfSea]

I would be concerned that the impeller has been overheated, which couple melt and partially restrict the water passageway. For flushing, I made up a Y hose adapter for flushing. This allows me to flush thru the muffs and engine flush hose at the same time. The local Yamaha lead tech told me this is how they do it at their dealership.

Great tip Capt Bill, I've been hooking up the hose 1st, then going to the muffs so everything is wet. That covers all bases, thanks!

 

[Hookster57]

Thanx for the replies, guys. I talked to the mechcanic again and he confirmed they used the muffs. He said he thought an airblock triggered the overheat warning and not to worry. Both the impellers are brand new. I'm going to get that Y adapter.....is it important to flush using both the hose and the muffs?

 

[seasick]

I got this from a certified Yamaha mechanic at Homosassa Marine:

Yamaha used to say that their engines could be run when using the flush attachment rather than earmuffs. But they ran into problems with people running their engines at high rpm. There were instances of overheating and also damage to the impellers. So now they say not to run the engine from the hose attachment.

The factory trained guys will still run them off the hose attachment, but they are careful to only do it for a short time and never over idle speed.

It's possible that you had a temporary air blockage in the upper part of the cooling jacket that triggered the alarm. As long as the problem doesn't persist, I wouldn't worry about any damage. The alarm goes off at just below 200 degrees. Car engines normally run higher than that, so no damage should have occurred as long as you shut the engine down.

As of 11 years ago, the Yami user's guide said not to run on the flush port. Many folks do so and depending on the water pressure and flow rate, they may be OK. Personally, I won't run that way. You also have to be careful when comparing the operational temps of outboards and autos since the auto cooling system is sealed and pressurized. The higher the pressure, the higher the boiling point of water. Outboards of course are not pressurized. The Yami t-stats opens max at about 140 degrees, 200 degrees head temp is a bit high and since there may be hot spots, boiling of the coolant is possible.

 

[seasick]

Thanx for the replies, guys. I talked to the mechcanic again and he confirmed they used the muffs. He said he thought an airblock triggered the overheat warning and not to worry. Both the impellers are brand new. I'm going to get that Y adapter.....is it important to flush using both the hose and the muffs?

No, flushing with both doesn't make it better. Again, a lot depends on your water pressure and flow rate. Even with muffs, if there isn't sufficient water flow, overheating is possible.
I don't buy the "air pocket' explanation at all. After the motor is shut down and after motor sits, it is one big air pocket. You may have had a sticking poppet valve. If you saw a good telltale ( pee stream) and the overheat alarm sounded and later went away, a stuck/sticky poppet is likely.
I guess it is good that it didn't happen again but I would keep a close eye on it.