OMC slight overheating

[grahamh]

Ok, so this is not a big issue, but I wanted to get everyone's opinions on it nonetheless.

My 1971 IMP with a Buick V6 and a OMC Stringer drive starts to overheat when I'm idling or moving very slowly. If I move even slightly faster, it cools right off again. The temperature gauge doesn't have numbers on it, but it moves from the middle to about 3/4 of the way up, it might go more, but I always start moving to cool it down.

Any ideas? My guess is the impeller, which I'll be changing at the end of the season anyway.


Thanks.

 

[WizeOne]

Re: OMC slight overheating

First off I would get a decent temperature guage then verify it with an infrared temperature gun.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96451

Temperature is a critical issue and can cause a lot of damage in a hurry if your monitering equipment is deficient.

That being said, your description sounds like a classic worn impeller. How old is it? To verify it, you could momentarily disconnect the line from the intermediate housing to the thermostat housing, while at an idle, and see how the flow from the impeller is. You should have a pretty stout stream, even at an idle.

This will eliminate the possibility that you have a worn/erroded impeller on the engine waterpump.

 

[grahamh]

Re: OMC slight overheating

Thanks.

I have no idea how old the impeller is, the boat was free (but it is in pretty good shape)

I just got it this season, it has 780 hours on it or so. I would not be surprised if the impeller is still original. (or is that not possible, given the age?)

And yes, a better temp gauge is on my list of things to do over the winter, I'll try to get a temp gun and verify the temp next time I'm out.

 

[NW Redneck]

Re: OMC slight overheating

It is possible it is the original. These stringers have pretty skookum impellers and when I changed mine (it was about 20 yrs old) it was still in fairly good shape. The PO was always careful about not even turning it over without water to the drive. Running it dry for even a short time can pooch it though.

Another thought is what shape are the manifolds in? Raw water or fresh water cooling? There could be rust/scale buildup in the mani's that's restricting flow at lower speeds. At that age it might be worth it to pull them off and inspect the passages and overall condition anyway.

 

[WizeOne]

Re: OMC slight overheating

As NW Redneck (now there is a real oxymoron) said, unlike the black anchors, OMC impellers are pretty tough. They are also bigger than the puny little black anchor impellers. As such, they can lose a little efficiency and still deliver ample water flow.

Howsomever, they still have their limits and however old yours is, it may be fast reaching that limit.

 

[NW Redneck]

Re: OMC slight overheating

As NW Redneck (now there is a real oxymoron)

What did you call me?!?
The NW is for North West. Not all us rednecks are from the south eh!