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CODY_YARBER07 05-25-2009 10:09 PM

Engine getting hot!!!
I just took my boat out for its first voyage of the summer and as I am idling out of the "no wake zone" I notice that the temperature gauge is almost in the red. I immediately turned the engine off and waited for it to cool down. After that I started it back up and drove to the houseboat with no problems. As soon as I get back to idle speed it heats up again. Not in the red but almost. Basically.. It only gets hot if you are idling. If you are going down the lake at speed then it runs a lot cooler than it usually does granted the water is still pretty cold. I have a feeling that it is either a thermostat or impeller but am not really sure and haven't checked either. If anybody has any clue what's going on here I'd love to know. My boat is an 83 S&S with the 351W. Thanks peoples!

Bongo 05-25-2009 10:13 PM

I expect you are on the right track. In order, I'd check:
- Screen at transmission cooler (or similar) on intake hose. Debris in the screen that is forced through at speed, but not at idle? (Happened to me a couple years ago with wood chips - lot of sticks on the lake.)
- Impeller.

The thermostat is possible, but I wouldn't think it'd matter whether at speed or at idle. Maybe at speed there's enough force to get more water through a narrow passageway.

Good luck.


bigmac 05-25-2009 10:35 PM

Weeds blocking the strainer on the transmission cooler (easy to check), or a few broken vanes on the impeller (change it out anyway), or thermostat. I'd address 'em in that order.

JDK 05-26-2009 01:25 AM

I bet your impeller is toast.
The reason the engine cools down at cruise is the the circ. pump will pull enough lake water in at higher rpm, but it won't at idle.

CODY_YARBER07 05-27-2009 12:54 PM

Can someone tell me where this strainer is?

bigmac 05-27-2009 01:06 PM


Originally Posted by CODY_YARBER07 (Post 601645)
Can someone tell me where this strainer is?

It's on the intake side of the transmission cooler. Look at the output hose from your raw water pump. It goes from there to the intake side of the transmission cooler. The transmission cooler is a flow-through tube (heat exchanger). The transmission circulates tranny oil around the jacket while raw water flows through it on the way to the engine. If you remove that 1 1/4 inch hose from the lower in of the transmission cooler, you'll be able to feel the strainer and clear any material that may be blocking the flow of water from the raw water pump to the engine. Weeds blocking it may impair that water flow to the point where the engine doesn't get enough water to cool it. Checking for such weeds etc is a simple process of undoing the hose clamp, pulling the hose off, and sweeping your finger around in it.

bainez23 05-27-2009 02:17 PM


bigmac 05-27-2009 02:45 PM

Might very well be the impeller, but even if it is, he still needs to check the transmission cooler strainer and clear it of broken impeller pieces. Might as well start there, especially since it's easier.

Rich-Atlanta 05-27-2009 03:27 PM

Check This
Cody, I had the same problem last year. The problem turned out to be the cover on the the impeller was worn on the inside and was loosing enough of its vaccume at idle to not pick up water properly. My problem was exactly as you describe yours as being. The engine would heat up at idle speed but as soon as the engine was above idle it would draw water and cool. I spent hours trying to figure out what was going on before taking it to a long time Mastercraft tech he had it figured out in about ten minutes. I think the cover was twelve bucks. Hope this helps - Rich

jwmiller 05-27-2009 05:35 PM

Drain plug
I just had an overheating problem this past weekend and it turned out that the drain plug on the transmission cooler had fallen out. No vacuum = no water.

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