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Normal running temp for mercruiser 50 v8

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jeremy27

Regular Contributor
"does any one know the normal

"does any one know the normal running temp for a mercruiser 5.0 v8,Took my boat out today and the temp went up fast while at idol,but when I get up to speed it will go down to around 160-180,I think the impeller is bad.Thanks"
 
""...temp went up fast whi

""...temp went up fast while at idol,but when I get up to speed it will go down ...I think the impeller is bad."

Good assumption; change it."
 
"I thought that to but it only

"I thought that to but it only gets hot when its at idol and not when I'm up to speed,but I will change it to,It won't hurt, Thanks"
 
"Could be zebra muscles, if no

"Could be zebra muscles, if not impeller.. Had the same problem withe a couple of 4.3's everything needed back flushing"
 
"a weak impeller can cause low

"a weak impeller can cause low flow at idle, when you raise the RPMS the impeller is strong or complete enough to pull enough water, could be a problem with the impeller housing too.."
 
""ray" I run the boat

""ray" I run the boat at Lake Allatoona in GA,"brain" I'm getting the impeller kit that comes with the housing and all. I'm going to check the therm just to make sure that its fine and nothing is in the way.Thanks"
 
"160 to 180 seems hot to me.

"160 to 180 seems hot to me. I have a 351 and it rarely ever gets above 130. Run the motor at dock and check the water flow out of the exhaust at idol and at 3k rpms. You should be able to tell if you have a water restriction, weather at the seacock, bad impeller or a system obstruction if the water flow seems to low."
 
"when I was at the lake I felt

"when I was at the lake I felt the manifolds and they felt hot which made me think the impeller was bad and not sending water to the motor.I cleaned the manifolds and there was alittle dirty, now the boat runs stronger and now I think the water is flowing free and the impeller now can't send enough water to cool the motor.I'm going to check everything and see.Thanks for all the info let you know what the problem was."
 
"I have a 2000 5.0 M/C raw-wat

"I have a 2000 5.0 M/C raw-water-cooled, I have owned since 2001. Temp once warmed up, stays right at 170. I replaced both exhaust manifolds and 4" elbows this year, primarily as preventative maintenance, and temp stays 3-degrees cooler, right at 167 now. I was a little suprised it didn't go much cooler, after seeing the water jackets appeared to be at least 50% clogged.

I was also told when replacing the exhaust items, to make sure NOT to use the restrictor style gasket on the riser. The restrictor style gasket has a small 1/32" hole on 2-sides instead of the oval opening used on all 4 sides of the gasket."
 
"A non "(closed coolin

"A non "(closed cooling)" system with a 143 degree thermostat will and should run at 150-160 drgrees when at idle and slow speeds. It will rise to 170-180 when running hard.

If your idle temp is below 140-140 it is either a stuck thermostat or weak/bad groung to the temp sender or weak/bad temp sender, or weak/bad guage.

Manifolds will feel hot, how hot is another matter. so if you can touch it it is probably OK"
 
"I replaced the impeller and t

"I replaced the impeller and took it to the lake yesterday it ran around 130-140 when at idle and got around 160 when I ran at full power for a min.it never passed 165 the whole time I was out there.And I ran it pretty hard at about 4600rpms for a good min.I think that is good...right,Thanks for all the info"
 
Also remember that with all th

Also remember that with all things bieng just so.........a 2-5 % varience between actual and what your sender/guage reads can be expected with a few years old components. Just the change in resistance due to weak connections/oxidized connections could alter the results by a small amount. So that bieng said if you see 140 and 165 then the actual and or hot weather readings will be 150+/- a couple degrees and 170 +/- a couple
degrees. Not unusual in hot weather and warm water to see 180 or so when running hard. When you start to get over 200 thats when something is wrong.
 
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