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V6 overheating at low rpm

"Rich,
Sounds like the wate

"Rich,
Sounds like the water pocket assembly is the culprit. If you have instaled the bellows already(using bellows adhesive) you can test the integrity by pulling on the bell housing outward toward you. (the hinge pins must also be removed to do this.) If the bellows expands and does not come away from the transom assembly then they are on ok. The trick to installing the gimbal bering bellows is to insure that the inner ring ( pre formed lip) of the bellows is correctly placed within the grove on both the bell housing and the transom assembly."
 
"Okay Joe, Thanks I agree and

"Okay Joe, Thanks I agree and hope that you're right on the w.p.assembly.I sent Troy the pics of it to his e-mail address."
 
"Didn't get the pics. May

"Didn't get the pics. May have been too big for our server. Try one or two at a time, or send them to my home email and I can get them uploaded later tonight. [email protected]"
 
"Here's the first one, I&#

"Here's the first one, I'll do the rest from home. (Time to go!)
193832.jpg


Looks pretty cooked!"
 
"OK Rich,
It looks pretty b

"OK Rich,
It looks pretty bad. at thos point you need to be certain that the drive will not be an issue. So, remove the upper water pump housing and inspect the lower base assembly of the water pump. Make sure that there are no cracks, and the base assembly is not warped. If this looks good then you may consider replacing the water pump upper assembly as well as the impeller.(I would do this.) Sierra sells a water pump kit that contains all the parts for the upper water pump change. Cost approx $26. If the water pump is redone as well as the upper water pocket assembly, then you know that there can be no issues commming from the drive. The concern that I have is that you removed the impeller already, I am not saying you did this incorrectly, you sound very mechanical, however, the curl of the impeller must be replaced exactly as it was removed. If this is not done correctly then there may be cause for failure down the road. In my opinion, the drive is already split, change the water pump. Just my $.02"
 
"Rich;
Is that water pocket c

"Rich;
Is that water pocket cooked or are those corrosion blisters? Try picking one open and see what you find. Is the rest of the drive corroded badly?

It is likley OK to reuse with new gasket and water tube seal, as long as the gasket surface is true.

For sure replace the impeller as Joe suggests.

The slinger has nothing to do with impeller seal. If you notice the impeller hub has a ridge on the top and bottom that seal against the upper pump housing and the base plate.
The slinger is intended to prevent sand and grit from entering the pump and causing scoring of the housing. It only needs to be pushed down the shaft lightly against the upper housing. A little 2-4-C is good..

Rod"
 
"Joe, the water pump assembly

"Joe, the water pump assembly was new last year . I removed it twice and disassembled the housing dowen to the base. I put things back together as listed in manual. (turning drive shaft clockwise while sliding assembly on etc..) so I am confident with that . The impeller looked just like new.
I am waiting for the upper waterpocket kit (should be here wed.) But just to be sure, I mught just get a brand new water pump kit anyway just for destiny's sake.
Rod, those blister are definitely from heat. All the damage is from the outside with no damage on the inside of housing. Thanks"
 
"Rich,
I boat in an enviorm

"Rich,
I boat in an enviorment where I pick up mud, sand and the like through the impeller. So I change the water pump upper assembly each seasons end. If you boat in a fresh water enviorment or one where you do not pick up sand through the pump then you can just change the impeller, and the lower gaskets. I have noticed that it costs as much to purchace the sierra upper water pump kit(includes all, and some other stuff I dont need) for the same money as just the impeller and he gaskets. You may wish to purchase the MerCruiser water pump kit. I have not found any difference between the after market and Mercruiser. Just my opinion. P.S. I was un aware that you had the pump changed just last year. Didn't mean to insult you"
 
"No problem Joe no insults at

"No problem Joe no insults at all taken. you guys do nothing but help me out. I do have another one of my million questions though ..How come the very bottom gasket under the water pump has only one passage for water, when the casting has two passages? I just hope that I have the right impeller part number for that boat.Thanks"
 
"a quick slightly off track ti

"a quick slightly off track tip for bellows install... When conencting the u joint bellows to the bell housing, you need to make sure the outer lip on the bellows fits into the carved recess in the housing, as mentioned earlier. BUT, you also must coat the expansion ring with a little lube before you try to pound it back in (i spent a long time before a neighbor showed me this trick) it will save you tons of time and cursin. Glad to see you are making way towards a solution!

--chris"
 
"Thanks Chris for the tip. I&#

"Thanks Chris for the tip. I'm trying to picture the expansion ring, but will reaquaint myself from the manual later. And at this point in this troubleshoot, I know better than to get my hopes up, but I hope that I am making way towards a solution also..."
 
"Rich,
I am not certain ho

"Rich,
I am not certain however I think one port allows the water to enter the pump area, and the other delivers the water up the upper housing via the impeller. I have included a parts diagram so that it will help you. At this point, if you are not removing the lower assembly, you need to be certain that the lower gasket is placed properly, then the wear plate and then the upper gasket. You can be certain of this if you carefully remove the entire gaskets including the wear plate in one piece. part numbers 14,15,16. #16 first then #15, then #14.( 17, 18, and 19 are all part of #17.)
http://www.glmmarine.com/pdf/MerCruiser_Catalog.pdf"
 
"Rich,
there is a silver r

"Rich,
there is a silver ring that pounds into the bellows end to expand it and press it into the housing walls, allowing the bellows adhesive to squish and seal up the bellows. That ring is a "futher mucker" to get in if you don't lube it(i'm assuming you have an alpha g2, alpha 1 gen1 had a std hose clamp arrangement, iirc)

--chris"
 
"Chris, I do have the Alpha on

"Chris, I do have the Alpha one gen.1 merc. And have the standard stainless hose clamp setup. I don't recall any ring that you described so any more info would be appreciated.Thanks

Thanks Joe also on that last e-mail.I was going to wait until I did a little something before I replied. I installed a new impeller and gasket kit and have the rest of my parts as of yesterday. I will tackle the bellows and try to get things back together soon. It still doesn't make sense to me that the somewhat small delivery port in the impellar housing can deliver enough water, to cool that motor. Why is the supply hose to the t- stat so large compared to everything back from there?
When I remove the bell housing, My plan is to put a hose directly on the new raw water hose that I previously installed . Is this okay to do this without the outdrive being on? Just want to make sure. Thanks again"
 
"Rich,
the ring only exist

"Rich,
the ring only exists on gen 2 drives. Gen 1's have the hose clamp setup instead of the ring--having done the ring i can say i'd prefer the the hose clamp
"
 
"To answer your 2nd qustion &#

"To answer your 2nd qustion "My plan is to put a hose directly on the new raw water hose that I previously installed",It will work. To answer the question "the impellar housing can deliver enough water, to cool that motor" the impeller spins at the same rate as the tach reads. Thats pretty fast. I thought the same thing, however it seems to work."
 
"I have reached a milestone..A

"I have reached a milestone..After pulling the drive, I installed a new waterpump and waterpocket. After mating the lower unit with the drive I left the unit on the sawhorses and made a connector for my garden hose so I could put water directly into the bellhousing. Joy..Rapture. The engine temp went up to 160 degrees and remained there. So we now know that the problem was in the outdrive, most likely the melted waterpocket. Hopefully. after redoing the bellows and putting things back together, things working like they should.."
 
"Great news Rich! So if all go

"Great news Rich! So if all goes well, you could have that thing in the water this weekend?

This is defineatly one to remember.

Good luck and keep us posted."
 
"The only thing the melted wat

"The only thing the melted water "pocket" could cause is the rubber gasket/seal that mates to the copper tube to collapse and restrict water.

Of course running cold "forced water" into the engine will keep it cool.

I have some suggestions here for you to look at and a couple of clearifications.

1. That gasket that sits on top of the water pump housing protectes the water pump from EXHAUST gasses!! it is actually a gasket if you will and is very important. It should be the thick rubber round washer looking style on the ALPHA 1 gen 1.

2. when you removed the water pump housing and gaskets did you inspect the water path comming from the lower unit? any broken impeller parts or any other foriegn matter in there?

2.before you replace the upper water pocket, hook up your hose to the water port that the water exits from the upper gear case and force fresh water back thru it to see if there may be something stuck in the water path in the upper gear case.

3. When you installed the water pump assembly in the lower unit did any of the gaskets tear? Are you 100% you put the correct gaskets in? If there is a tear in one of the gaskets you could be introducing air into the input side of the impeller housing.

4. If all of the above fails and based on your temps from your IR gun my thoughts are the sending unit or gauge is reading wrong.

I have seen many times and spent many hours troubleshooting overheating issues that turned out to be a sending unit that jumped from 120-130 straight to 200 in a very short time.
When you introduce fresh cold water from a hose you could have a marginal impeller and the engine would still stay cool as long as the water pressure was adequit.

Also here is a test to check the ability of the impeller.

Attach the ear muffs to the lower unit. Turn on your water so there is just enough water comming out of it to blow out the sides of the ears.
Start your engine. The impeller should "suck" the water in and no water should be shooting out past the ears. You should be able to increase your water pressure and this will continue to be sucked in untill the water hose pressure overcomes the impellers ability to take any more volume.
The only other far out thought would be that the exhaust flappers got crispied and the rubber fell off if not the entire flapper and is blocking the exhaust at the rams horn after the elbows. ( this is a bit far fetched but possible)

Goodluck"
 
"Thanks for the info. Everythi

"Thanks for the info. Everything that you mentioned has been checked and checked again and they are all great tips. The melted waterpocket to me looks like where it has been leaking, only when The motor was up to 3000 rpm,s was when it would finaly suck up enough water to cool. Low rpm's it most likely was spraying out into the outdrive.
The temp gauge has never jumped, but would always slowly rise to the temperature,another words, it has never acted up..
The thing that sold me was when my temp gauge leveled of at 160 degrees, all hoses(by feel) felt just right. incoming hose was cold, bypass hose to circ. pump was warm,middle hoses to exhaust elbows were cool.And t-stat hoses to manifolds were warm. Thanks"
 
"Rich,
Good news. The next

"Rich,
Good news. The next thing is if you are tearing down the bell housing again to redo the U joint bellows, then why not replace them.This way you dont have to do this job again. Also be careful when replacing the trim limit and trim senders, if you move it you will loose your trim limit and sender positions and have to readjust them. Not a big problem. Glad to see you have made great progress."
 
"Joe, the bellows are new and

"Joe, the bellows are new and I already marked the senders from last time so I can put them back the same way.Thanks alot"
 
"VICTORY AT LAST... I got ever

"VICTORY AT LAST... I got everything meticulously back together yesterday and things are working perfect. The engine gets up to almost 170 degrees and the t-stat opens, and goes back to 160 degrees and hangs there on idle for as long as you want.
I know that I haven't tested the boat on the water yet, but I'm very confident that things are in order.The hoses going in and out of the t-stat don't get hot anymore. They are warm except for the inlet hose which of course is cold.
I want to thank everyone of you guys that helped me out.especially Joe and Troy... who has been with me from the start.I have learned alot and feel very confident in doing most , if not all things myself now.
Thanks again to all of you guys. There's about 10 of you that helped out. This is a great site, and one that I will be sure to visit from time to time .. Cheers , Rich"
 
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