mercruiser 5.0 mpi overheats at idle

[nauticool]

Need Help Please!

Have a 2005 5.0 mpi (78hrs) with an alpha 1 gen 1 (1990) ish used in freshwater, the first 30 hours were saltwater. Tonight i was moving it to the marina as it will be lifted out tomorrow for a couple of weeks.

As i left the pontoon at approx 750rpm the temp kept rising to 225f so i shut the engine down. To drift downstream in the dark!!! White face moment

I am extremly worried there was no warning buzzer to tell me to do so but thats for another day. I let the engine cool and ran it again.
In the past the engine would heat, at idle, to 180-200 but when revved it would cool immediatly to 160, i just thought this was a characteristic of the engine.
Now everytime i let it idle it heats to 225, wont let it go higher, then rev it and it comes down to normal temp. Any higher speeds other than idle the engine is perfect.
Another new thing i have noticed is a dry bearing noise from the fwd port side of the engine, at idle. oiled all the pullys etc but hasnt stopped the noise. Maybe connected to problem?
The outdrive was serviced last year with new impeller, its done 30 hrs since.
Not sure if the engine is overheating or the temp gauge is incorrect.
I have read online to either check impeller for broken blades, check ball/spring in hose attached to thermostat and upper manifolds or crushed cooling pipes. Concerned about the dry bearing noise too.

If anyone has had similar problems or any ideas please help. will try suggestions at the weekend.

Many thanks in advance

 

[Don S]

Re: mercruiser 5.0 mpi overheats at idle

How long has it been in the water?
Obviously, you have a new engine from the original 1990 engine, did the exhaust manifolds and risers get replaced with the new engine?

I would suggest you get one of those IR Temp guns and verify the engine temp to see if it actually is overheating or not.

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

got a fluke ir temp gun. is the best place to take a reading on the top of the thermostat housing?

been in the water since august and had a good season out of it. not sure on risers, look old, but manifolds look new

how hot is too hot? im concerned i may have already damaged something today, got to max 225f but still runs ok

thanks Don,

Glenn

 

[Fun Times]

Re: mercruiser 5.0 mpi overheats at idle

Hello, I know you say you have an alpha drive and the impeller is in the drive, But with the engine you have it does come in two styles, One is for an alpha and one for a bravo drive set up, There is a 50/50 chance you have a bravo style engine set up, And if so then you could have an extra impeller that is belt driven by the engine, And that could be the new noise you hear if that impeller is going out in anyway.

One way to know if you have this impeller is by, While looking at the engine pulleys from inside the boat see if the belt goes to a pulley down on your left side, It would be sitting a little bit lower then the fuel filter area if you have the bravo style engine set up that is, If you have the alpha style engine then the pulley should not be there and there should be an open space down in that corner just to the right of the fuel filter area.

Do you have an engine serial number?
We might be able to see what style engine you really do have if your not sure.

http://www.mercruiserparts.com/selectSerailRange.asp?doc_nbr=5.0L+MPI+ALPHA/BRAVO

If you have a bravo style engine here is what it would look like.
http://www.mercruiserparts.com/Show...=11652&bnbr=270&bdesc=Sea+Water+Pump+Assembly

 

[Don S]

Re: mercruiser 5.0 mpi overheats at idle

Anything over 180? is too hot.
Time to pull the risers and inspect. Is your engine raw water cooled, or do you have a closed cooling system.

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

hi boat tech,

This will be interesting to know as i assumed there was only an impeller in the outdrive

ser no OW385827
model MCM 5.0MPI

outdrive alpha 1 gen 1

ser OC893180

Thankyou

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

Engine is raw water cooled only but is used in freshwater. has been used in the past in salt water

 

[Don S]

Re: mercruiser 5.0 mpi overheats at idle

I would have to guess it's an Alpha engine since the shift interrupt system works. The Bravo engine doesn't have the shift interrupt system designed into the ECm.
All you have to do is look at the front of the engine. Do you have a pump that looks something like this?

 

[Fun Times]

Re: mercruiser 5.0 mpi overheats at idle

hi boat tech,

This will be interesting to know as i assumed there was only an impeller in the outdrive

ser no OW385827
model MCM 5.0MPI

outdrive alpha 1 gen 1

ser OC893180

Thankyou

Nope your ok it an alpha.
ENG: 0W385827 model number 4M4122LTT 1998M MERCRUISER 5.0L MPI ALPHA DRAIN ENG ONLY 5.0L ALPHA MPI

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

whats a shift interrupt system? im worried i had no warning of an overheat from the ecu/ecm?

 

[Don S]

Re: mercruiser 5.0 mpi overheats at idle

Don't worry about the shift interrupt system, it's there so you can shift the alpha style driver in and out of gear. It has nothing to do with the cooling, just me thinking out loud.

Can you take a picture of your exhaust manifolds and risers? Or, if you know, do you have the dry joint style of manifolds or the original 90 style manifolds.
If you have the old style, I would bet you have the original 1990 manifolds and risers. If that is the case, and it was used in salt water in the past, they could be your problem.

 

[Fun Times]

Re: mercruiser 5.0 mpi overheats at idle

I May catch some heat for this, But oh well, It's my opinion

Make sure on your next impeller change you use an (OEM) style impeller from MerCruiser and not an after market style impeller.

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

Forgot to mention yesterday lots of steam coming from the water. Water temp here is about 8c.
Boat should be out of water now so will take some pics later.

 

[ENSIGN]

Re: mercruiser 5.0 mpi overheats at idle

Disconnect the water inlet hose from the thermostat housing and start the engine.You should have a good steady stream.If not check the impeller for wear and debris in the P/S cooler.Do this test with the boat in the water.

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

boats out now. noticed today the pick up pipe on the outdrive was 40%squashed when trimmed down so trimmed up a bit and put grips on pipe to reform to proper size. with no avail... still same symptoms. just thought id mention it.

idle is 600rpm is this low for pump?

Don, the link is for you, hope its suitable.

will pull outdrive tomorrow to check pump etc and also remove risers.

am i right in saying the order is manifold, riser, elbow, exhaust? Just so i know the terms and we are talking about the same thing. i am mechanically minded just not so much on the marine side


http://www.youtube.com/watch?v=cRiKeiQ3BLo

 

[Don S]

Re: mercruiser 5.0 mpi overheats at idle

The youtube pics worked fine, you do have the 2005 version of the exhaust manifolds (Dry Joint) and are probably not your problem.
Which pickup pipe are you referring to?

Also, you only have a raw water pump in the drive, not on the engine, and 600 rpm should be fine. When you get to the pump, I would be interested in seeing pics of the housing and the impeller. If the housing is warped, or melted a little bit for a previous overheat, it could be causing the problem. Did you use new gaskets the last time the impeller was replaced?

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

the pick up pipe is black rubber, maybe 3/4". Its the only one running along side the bellows.

bought the boat in july last year and just found an invoice from 05/03/09, a year, or 30 hours ago!

items changed are

water pump repair kit, part no 47-89984T5
the crushed hose i was talking about part no 32-4172533
all bellows
various gaskets and o rings
drive oil
assy-shift cable 865436A02

over a $1000 bill!

Went in with a shift problem, engine stalling on shift

 

[Fun Times]

Re: mercruiser 5.0 mpi overheats at idle

the pick up pipe is black rubber, maybe 3/4". Its the only one running along side the bellows.

bought the boat in july last year and just found an invoice from 05/03/09, a year, or 30 hours ago!

items changed are

water pump repair kit, part no 47-89984T5
the crushed hose i was talking about part no 32-4172533
all bellows
various gaskets and o rings
drive oil
assy-shift cable 865436A02

over a $1000 bill!

Went in with a shift problem, engine stalling on shift

More then likely that hose is your problem, Sounds like they did not install the hose right the first time, You should give them a call and see if they are willing to make it right. Good luck.

 

[Fishermark]

Re: mercruiser 5.0 mpi overheats at idle

I would still be looking carefully for pieces of the impellor in the various water passages. I have found them in the thermostat housing - AND - in the outdrive itself. In the tube running from the water pump housing.

Actually, my dad recently purchased an old boat. I rebuilt the engine for him and we took the outdrive off and had it serviced at a local shop. They said it pressure checked fine, replaced the water pump, etc and I put the outdrive back on the boat. My brother and I had a heck of a time diagnosing an overheat situation. That is when the pieces were discovered in the upper part of the outdrive itself. Just something to check.

 

[nauticool]

Re: mercruiser 5.0 mpi overheats at idle

Thanks everyone for your suggestions, will be trying them all tomorrow.

Can anyone tell me if i need any special tools to remove the outdrive to get to the water pick up hose? It looks like i need something when the trim sender is taken off, large hex shape, or is this just a large allen key? Anything else?