Temperature issues Help please Mercruiser

[air2raley]

I have a 1989 searay with a 4.3 liter mercruiser. When I first start the boat from cold the temp guage will rise accordingly to the 190 degree thermostat setting. Once underway the temp guage will drop to a minimum reading and stay there. Once I get back to idle the temperature will rise way beyond the termostat setting and it will take adding RPM to the engine to get it to drop. Once underway again the temp will fall to a minimum level on the guage. The termostat has been replaced as well as the temp sensor. All hoses are clear of any obstructions. It still has the issue. Has anyone seen this problem?
thanks

 

[fishinpa]

Re: Temperature issues Help please Mercruiser

sounds like ya may need a water pump impeller..

also i dont know about the 190 thermostat
is it what is called for on your v-6 ?





fish

 

[air2raley]

Re: Temperature issues Help please Mercruiser

thanks the termostat is a 140...sorry. Thanks for the reply. That was fast and helpful.

 

[full stringer]

Re: Temperature issues Help please Mercruiser

check your water pump belt see if its slipping if your impeller was bad it should overheat no matter what idle or running could it be your circulating pump you will have to pull hoses and see

 

[extreme76]

Re: Temperature issues Help please Mercruiser

I have you considered a bad gauge? My trim gauge will act that occasionally. I would at least consider the gauge.

 

[nitrosteve]

Re: Temperature issues Help please Mercruiser

I just had almost the same exact situation... Here is the link

http://forums.iboats.com/showthread.php?t=411278

Fix was the pickup tube was not aligned correctly.

 

[Bondo]

Re: Temperature issues Help please Mercruiser

Ayuh,.... In Any overheat situation, Changing the Impeller is the very 1st diagnostic/ repair step.....

 

[180shabah]

Re: Temperature issues Help please Mercruiser

check your water pump belt see if its slipping if your impeller was bad it should overheat no matter what idle or running

Issues with the seawater pump often first show up with increased temp at idle when the pump is spinning slowly. Higher revs = more waterflow, but he is definitelyon hte ragged edge here.

There is no belt to check, the pump is driven directly from the shaft in the drive.

 

[air2raley]

Re: Temperature issues Help please Mercruiser

thanks for everyones input. I know I'm way overdue for the impeller replacement. I disconnected the hose going to the Tstat and there is some water flow but only trickles out. Other than the gauge being bad I don't understand how the T guage drop to 100 degrees once underway. Once back to idle the gauge increase to a too hot codition due to no water flow from the impeller pump. How do you check for a good T-gauge?

 

[Don S]

Re: Temperature issues Help please Mercruiser

If all the vanes on that rubber impeller are bent over and will not straighten out, then it WILL overheat at idle, but with increased rpm they will pump a little more, plus the force of water in the pickup will push more water to the engine.

You are trying to blame the problem on the gauge, but it seems to be telling you where the problem is, you just don't want to believe it.
Pull the impeller and look at it. Especially if it's over a year old.

 

[air2raley]

Re: Temperature issues Help please Mercruiser

I'm off to the lake next week and will immediately replace the lower pump impeller. I'll let you know how it turns out. I'm embarrased to admit how old this impeller is.......let's just say more than 5 years old. thanks for the help and advice

 

[bigskiohio]

Re: Temperature issues Help please Mercruiser

I disconnected the hose going to the Tstat and there is some water flow but only trickles out.?

you have your answer. mine was cooling fine but when i took it apart it had two fins broken off.

 

[180shabah]

Re: Temperature issues Help please Mercruiser

let's just say more than 5 years old. thanks for the help and advice

...and you still don't know why you are having cooling issues????

 

[air2raley]

Re: Temperature issues Help please Mercruiser

fixed the temp problem. I replaced the impeller (it was hard but not broken).....after that replacement and a lake test it was doing the same thing. I noticed the engine water pump leaking at the shaft so I replaced it. When I took the old pump off the impeller had completely rusted away into nothing. There was nothing left but some rust scale. One the new pump was put on the engine is now regulating at 145-150.
thanks for everyone's help on this.

 

[180shabah]

Re: Temperature issues Help please Mercruiser

Glad you got it all figured out.

Hopefully you replaced the circulating pump with a marine one instead of the auto version you just took of....