How hot should my engine get ?????

[pedroofn19]

I have just bought a late 80s 90hp 3 cylinder mariner, and when the engine is run on the sea it gets very hot. There is water pumping through the engine well but the top of the engine feels very hot after 5 minutes of running around. Ive had a few outboards and Ive never felt an outboard get this hot, even after 3 hours constant use.
SO HOW HOT SHOULD MY OUTBOARD GET?????

 

[pedroofn19]

Re: How hot should my engine get ?????

???

 

[RogersJetboat454]

Re: How hot should my engine get ?????

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Give us more than 3 minutes between posts to respond. This is a forum, not a chat room. Most of us are at work on this side of the pond.

How hot is hot? Burn your hand hot in a few seconds, or hot but you can leave your hand on it for a few seconds hot.
You may want to get an infrared temp gun, and measure the temp of various components then post the results back here. Readings in ?F please.

You say it's pumping water, but that doesn't mean its pumping enough water. If the impeller hasn't been replaced in the past couple years, it should be replaced. If the previous owner didn't tell you when the impeller has been replaced, or has never heard of an impeller, then the impeller needs to be replaced.

 

[pedroofn19]

Re: How hot should my engine get ?????

thanks for the reply. The impeller has had 20 hours of use since new. I can hold my hand on it for as long as I want to, but if it was hotter then I wouldnt be able to keep my hand there for long. And that was with only 5 minutes use, wouldnt the engine get hotter the longer it is running? I dont know to much about engines and any help is much appreciated. Thank you.

 

[RogersJetboat454]

Re: How hot should my engine get ?????

thanks for the reply. The impeller has had 20 hours of use since new. I can hold my hand on it for as long as I want to, but if it was hotter then I wouldnt be able to keep my hand there for long. And that was with only 5 minutes use, wouldnt the engine get hotter the longer it is running? I dont know to much about engines and any help is much appreciated. Thank you.

Ideally if everything in the cooling system is functioning correctly, it shouldn't get much warmer than after the 5 minutes of use. You can hold you hand on it, that tells me it's not getting raging hot.

This again would be a good time to get a hold of an IR temp gun and check the temp every couple minutes. If after that 5 minute period the temp continues to climb, you probably have issues.

Hopefully one of the Merc Guru's will chime in, and be able to actually give you some more ideas, ideal temps, and tell you whether or not your engine has a T-stat that should be replaced as precautionary maintenance.

 

[Texasmark]

Re: How hot should my engine get ?????

The thermostat probably starts opening at 143F, a common temp for Mercs, at least the ones I have serviced. A US domestic hot water heater in the Normal (center adjustment range) is set to 140F. That should give you an idea what normal hot is.

The stat starts to open within some tolerance of the stamped temp so you could gain 5-10 degrees on the bad side and it "starts to open" meaning the thermally sensitive spring that operates it will expand more as the water gets hotter and at some elevated temp it will be full open.

The over temp sensor is set to 190-195 (forget which) and resets at 172 as I recall. Plenty of room for your stat to do it's thing.

If it is working correctly and seems hotter than previous engines, then possibly they did not have stats. Merc was late in the game coming online with stats. Probably figured that their 40kv ignition would solve most problems and stats were just something else to fail.....point well made.....having had stats fail in two of my engines over the years and one (OMC...stat, but no OT warning sensor/horn...1975) cost me a powerhead overhaul having to be bored, over sized pistons/rings and all.

HTH,

Mark

 

[pedroofn19]

Re: How hot should my engine get ?????

Ok thanks guys, I have just ordered an IR temprature gun so I can find out how hot the head is getting. I will let you know in a few days. Thanks for your input.