opinions on near overheat cool down

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crazy charlie

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I have had a consistant problem of rising engine temp at idle on both my 5.O rwc XL mercruiser i/os .If I tap up the idle 1-200 rpms,the temp comes right down .While idling on muffs ,the temp climbed to just shy of the red range of the temp gauge.I tapped up the rpms 1-200 and the temp came down to normal range 145.My mechanic told me that I should have turned off the motor and let it cool.Any opinions on which was the best action to take after a near overheat at idle.Charlie
 
Bondo

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Re: opinions on near overheat cool down

Ayuh,..........

I think you did Right Charlie............
 
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crazy charlie

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Re: opinions on near overheat cool down

thanks for the reply Bondo !!! How was you summer boating season???? One of the best I can remember in recent years as far as the weather and water conditions.I dont think we missed a weekend all season.Good to hear from you and I hope all is well with you and yours !! Charlie
 
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SFT2

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Re: opinions on near overheat cool down

crazy charlie said:
I have had a consistant problem of rising engine temp at idle on both my 5.O rwc XL mercruiser i/os .If I tap up the idle 1-200 rpms,the temp comes right down .While idling on muffs ,the temp climbed to just shy of the red range of the temp gauge.I tapped up the rpms 1-200 and the temp came down to normal range 145.My mechanic told me that I should have turned off the motor and let it cool.Any opinions on which was the best action to take after a near overheat at idle.Charlie
Click to expand...


I'm still learning all this boat specific stuff, but from my experience with every other kind of liquid cooled engine I've dealt with (cars and bikes), it sounds like either the idle is set too low or there's excessive clearance in the water pump. I'd lean towards the 2nd, personally.

I'd have brought the idle up. Shutting off the motor with the engine hot means there's no cold water to cool it down. Hmm, wonder if a Meziere electric water pump for a SBC could be adapted to fit a Mercruiser. With an electric pump you could shut down the motor, but leave the pump running.
 
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crazy charlie

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Re: opinions on near overheat cool down

Yes,I have been planning on raising the idle a bit but never get around to it.Water pumps are recent to new so I am sure thats not it.Running a water pump w/o the motor running can lead to problems with mercruisers that have valve overlap.I am not sure of the specific years but my 84 mercr.5.7 had that design.Charlie
 
MikDee

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Re: opinions on near overheat cool down

Maybe your water inlet hose in the drive is slightly kinked at the bend, this happens once in awhile,,, take a look.
 
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crazy charlie

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Re: opinions on near overheat cool down

Wish it was a simple find Mik.I have been thru everything including the tubes which are recently replaced.Water pump,circulator pump,tstat and housing,manifolds and risers,spring balls.Only happens when I am idling at the minimum rpms.Same on both motors.Charlie
 
BAYLINER185

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Re: opinions on near overheat cool down

Does it overheat in the lake?

They say only to run the muffs for 5 minutes maby your runnign it too long on muffs or your not allowing enough water to flow from your hose.

I havent run my new boats on muffs but I think I remember my old boat to run hotter on the muffs. I really dont remember for sure though.
 
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crazy charlie

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Re: opinions on near overheat cool down

BAYLINER185 said:
Does it overheat in the lake?

They say only to run the muffs for 5 minutes.
Click to expand...
I dont know who "THEY" are ,but "THEY" are wrong!!! You can run on muffs as long as you like as long as the water source is uninterupted.Charlie
 
Bondo

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Re: opinions on near overheat cool down

Ayuh,.........

My 4.3LX/ Alpha 1 has done this to some extent since I built it,.... Over 700hrs ago.......

I'm putting in a Complete raw water pump this winter to Help with the issue.....

I use the boat for Trolling, so it's a somewhat constant issue,.....
Deploying the Trolling Brakes,+ bumping the throttle to 1000rpms Helps Alot......
I caution Against turning Up the idle of the motor,....
Only because it's Hard on the drive with the set Idle is above 700rpms....
So,........
I keep the set Idle low,+ bump it up with the throttle................;)
 
Don S

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Re: opinions on near overheat cool down

What year is your engines Charlie?
I assume you have the proper exhaust riser gaskets?
What type thermostat housing do you have?
 
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CharlieB

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Re: opinions on near overheat cool down

A couple of questions.

Does it heat quicker when on the hose vs in the water?

How deep are the drives while at idle in the water, in relation to the o/d water pump?

Even a very small warp in the stainless upper housing of the water pump can cause the gasket to fail, symptoms exactly as you describe.

Get a few big butted girls in the back of the craft so the water pump is submerged and retest at idle. when it idles at normal temp then pull the LU and fix the pump.
 
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crazy charlie

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Re: opinions on near overheat cool down

Don S said:
What year is your engines Charlie?
I assume you have the proper exhaust riser gaskets?
What type thermostat housing do you have?
Click to expand...

Don,the motors are 1988 5.0xl mercr. with alpha drives RWC. Correct man,risers,gaskets,no sealant on gaskets.The stat housing I assume is the standard one with the stat housed in the top with long bolts and t/balls in front.Tough to describe w/o having it in front of me.Charlie
 
Don S

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Re: opinions on near overheat cool down

This one????
 
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crazy charlie

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Re: opinions on near overheat cool down

No don,I dont think thats it.That one looks like a 1984 that I once had.I will take a look in my basic marine parts book to see if I recognize any.Charlie
 
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crazy charlie

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Re: opinions on near overheat cool down

I cant find it in the catalogue.I will have to take a detailed look or a snapshot this weekend.I think my t is not raised like the one in your diagram.Charlie
 
Don S

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Re: opinions on near overheat cool down

More like this?

Untitled2.png
 
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crazy charlie

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Re: opinions on near overheat cool down

Thanks Don.I am not used to reading svc bulletins but I think this is telling me that I may have a newer housing that needs me to remove the check balls.Since I wont be able to run w/o the checkballs until spring do you see an easy way that I can tell if this is the case???Charlie
 
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