Overheat in water, not on muffs

[Dafishguy]

1989 210 striper with cobra 5.0 omc ford 302. Block replaced in 2009, new risers/thermostat and impeller last year. Been running great this year. Have five or six 40-80 mile offshore trips in so far this season. Ran offshore on Saturday, no problem, ran around locally Sunday, no problem. Woke up Monday morning started engine to warm up my breakfast burrito on the manifold and go use the restroom on shore. Get back and engine is idling fine but notice the temp gauge is high. So I shut it down and check for kelp or a bag on the out drive. Nothing there. Both manifolds and risers are hot, so I eat my burrito and let the temps come down. Try again, temps go up fairly quickly. Cool down again and then idle it over to the lift, temp is up again. Pull the boat out and check inlets for clogging, nothing there. Hook up the ear muffs and fire it up, temp goes down to normal right away and stays there for over five minutes with no issues. Hmmmm. Pull the cover and check the impeller. It looks perfect. Was not able to put back in water yet. And I live a couple of hours away from the boat, so trying to do some research before I'm down there again.... Any ideas? Thanks, Tim

 

[MRS]

Did you pull the impeller out of the housing and look at the whole impeller?

 

[MRS]

Did you pull the impeller out of the housing and look at the whole impeller?

 

[Dafishguy]

I did not remove it from the housing but I did remove the housing, it is very easy to see that it was completely intact and looked brand new, it was just installed less than a year ago, with no abuse and less than 50 hours on it. I was by myself so couldn't verify if the drive shaft it sits on would spin when cranked or running, but the shaft looked good and solid, I was unable to budge it with the engine off, but I would assume that to be normal?

 

[Lou C]

No Title

The impeller can look good but not pump right. How much wear was on the wear plate? And if you pull out the impeller, how much wear is on the stainless steel cage in the housing?
When I do a Cobra impeller, I do a few tests before putting the new one in.
1) with impeller housing off, hook up water muffs, have someone turn on hose, hold muffs tight to lower. Water should squirt out of right hand opening in impeller mount area.
2) Disconnect raw water intake hose at thermo housing. Stick your garden hose in there and clamp it to make sure it doesn't come out. Turn on water. Water should spurt out of the left hand opening.
3) do the same with each manifold hose.

This tells you if there are blockages or not.
Is this a salt water boat, if so when were the risers/manifolds last done? 5-7 years you can expect them to clog with rust if in salt. If you're saying off shore I'm guessing salt water.
If the boat was left in the water, even if painted with anti fouling, you can get marine growth on that intake screen in the lower unit and it will cause overheating. Even if you don't see barnacles on the screen, they can be growing up above it. You may need to split the drive to get them all out. I did lol.....

 

[Dafishguy]

Thanks, going to check out some things this weekend.