1990 Merc 4.3l water temp a little warm?

[cloud_master]

Running my ‘90 4.3L’s this weekend, I noticed my water temp indicating about 163 on my stbd gauge. Port was indicating 140-145. Can’t say that I stare at the gauge, but remember seeing closer to 145-150. I can bring a temp gun next time out and shoot the thermostat housings and see how accurate the gauge is. I always assumed in a perfect situation, the the gauges should indicate 140 with the 140 degree thermostats. What is an acceptable temp range for these motors working pretty hard pushing a cruiser?

I may install some water pressure gauges on these engines for next year. I hate the idea of my water pick ups being plugged and baking my exhaust until I see a steady increase in water temp on the engines.

 

[Rick Stephens]

If in salt water they need to stay 160 or below. If in clean water then can run another 10 higher.

 

[cloud_master]

If in salt water they need to stay 160 or below. If in clean water then can run another 10 higher.

Fresh water boat. What's the significance of maxing out at 170 degrees for fresh water use? Just curious for my own knowledge. Thanks.

 

[Rick Stephens]

You hit 170ƒ in fresh water and bubbles start to form. Those bubbles prevent heat transfer. Anything over 170 and you will have hotspots that are boiling and causing steam, which also won't transfer heat. Only way to run 170 and above is with closed cooling and some pressure to prevent the bubbling. Salt will increase that, BTW. And the extra heat in salt water makes it more corrosive.

 

[Nextelbuddy]

there are 2 thermostats, 140 degree and 160 degree. is it possible you have a 160 thermostat in the starboard engine and a 140 in the port engine?


i just finished searching a ton on google and that's how i found that out.

 

[harringtondav]

1990 vintage gages and senders/connections can be misleading. I'd take the gun and verify actual temps. From recollection 140 deg stats were the standard before your vintage. 160 degree stats came on the LXI Thunderbolt V engines after 1997.

If your thermostats are 30 year old it may be time for new ones. There are also many other causes for overtemp, starting with the outdrive impeller in the hot engine.

BTW, my pal's 1988 twin inboard Cruisers 350 always shows one engine 20 degrees warmer than the other. Four gages (main helm and fly bridge), two senders, thermostats, and related connections. Lots of room for confusion. He changes the raw water impellers and cleans the strainers regularly. Still a 20 degree difference. Go with the IR gun to settle any doubts.

 

[cloud_master]

You hit 170ƒ in fresh water and bubbles start to form. Those bubbles prevent heat transfer. Anything over 170 and you will have hotspots that are boiling and causing steam, which also won't transfer heat. Only way to run 170 and above is with closed cooling and some pressure to prevent the bubbling. Salt will increase that, BTW. And the extra heat in salt water makes it more corrosive.

Ok, thanks for the info.

 

[cloud_master]

there are 2 thermostats, 140 degree and 160 degree. is it possible you have a 160 thermostat in the starboard engine and a 140 in the port engine?


i just finished searching a ton on google and that's how i found that out.

The thermostats were changed last spring. The impellers were also changed last spring. I’ll change both for next season.

I’m going to take my IR gun with me and shoot the housing next time out. I’ll also get a new thermostat and gaskets to keep in the boat just in case. I’m making a couple hundred mile trip in October and I don’t want to get stuck.

Is there a high water temp alarm on a ‘90 merc 4.3? What is the trigger temp?

thanks

 

[Bt Doctur]

click to enlarge

 

[Chris51280]

I have the same engine. My thermostat reads 160 at the gauge pretty consistent. I thought I had a bad sending unit and checked it in hot water and the resistance. The new thermostat is the 142 degree one. Either my gauge is not correct or there is some other ghost in the system. At idle mine goes up to 185 per gauge if it is very long like getting tubers or skiers in and out. as soon as i go over 1200 rpm the temp drops down.