3207 mercruiser - overheating???

[js_325i]

Hello,
I'm new to this forum and have run into an issue with my boat..

2 weeks ago I was out running on plane and noticed that my temp gauge read 240...
Immediately turned the engine off and returned to port on one engine...
Figured the Impeller, opened it up but it was perfect....thermostat looked good too
Changed both the impeller, thermostat and the alarm sender (looked in rough shape).

Turned the engine back on and the gauge immediately when to the 200 mark - I know the engine could not be that temperature after 30 seconds.

Put my port and starboard engines on and compared surface temperature readings....they are within a couple degrees difference. With the exception of the bit hose returning from the engine to the thermostat housing 12 deg higher.

On a side note, there is a difference of water exhaust between the two engine - about 20% less on the troubled engine.

Any ideas or help would be appreciated.

Thanks

[hausherrs]

I dont own a Mercruiser. But from what I understand they are raw water cooled?

I would start at the through hole and work my way all the way through to the exhaust.

1) Check the through hole to make sure there isnt any blockage.
2) You stated the impellers are good, but I would also check the wear plates and the cam plate. People replace the impellers for years and often never look at those things. There should be a major service kit that includes those pieces.
3) You said you replaced the thermostat. I have read of people putting them in backwards. And it would cause the problem you are seeing.
4) Have your risers ever been replaced? Blockage from calcium and rust can block the flow of raw water. I would try replacing those if its been a few years.

If those things check out then have the engine looked at. Bad head gaskets have been known to cause overheating.

Do everything in pairs. Whatever you do to one engine, do it to the other. That way down the road you dont have one engine underperforming.

[mrsparkj]

Check your heat exchanger for proper fluid level. This happened to me, come to find out I had a leak there which caused all my fluid to drain out and cause my port engine to run high. Fixed leak, added fluid and was good to go! Good luck!

[throwback2]

Back flush the oil cooler,if you don't have sea strainers,that's where the blockage usually begins.

[Viper]

I agree with all the above, there are several things that will cause this symptom. That vintage didn't usually come with strainers so you may have a clogged cooler if strainers don't apply in your case. It would help to know if you have raw water or fresh water cooled units. Do you know if she was a salt water boat at one time? If so, the elbows and risers if applicable are suspect. Do you see any steam from from that exhaust?

[bobeast]

If the gage shoots up to 200 after 30 seconds, I'd start with the simple stuff. swap the sender wires. If the problem doesn't follow the sender wires. swap the gages. If the problem doesn't follow the gages, only then would I start to get serious about cooling issues.