Boating - - BOAT DOCTOR Q&A -

I have a 1988 2.5-liter en­gine and MerCruiser stern­drive with a cool­ing is­sue. Af­ter find­ing out my me­chanic charged me for a new wa­ter-pump impeller and never in­stalled it, I de­cided to make the re­pair on my own. I in­stalled a Sierra impeller kit ac­cord­ing to the Mer­cury re­pair-man­ual in­struc­tions. Af­ter I started the boat on muffs, it pumped wa­ter and cooled fine, but af­ter it sat for two days, it would not pump any wa­ter up to the en­gine (on muffs). I pulled the lower unit and no­ticed I had pinched the rub­ber gas­ket for the pickup tube where it goes into the up­per part of the drive. I re­placed that gas­ket and in­stalled an­other com­plete impeller and hous­ing kit. I ran the boat on the muffs again, and ev­ery­thing seemed fine. Af­ter it sat about four days, I hooked up the muffs, started the en­gine, and it would not pump any wa­ter. (I never over­heated the en­gine and never ran it at high rpm.) Dur­ing all of the above, the boat was on the trailer, hooked up to the muffs, and the drive was in the down po­si­tion. I tilted the drive up to the trai­ler­ing po­si­tion, started the boat, and it pumped wa­ter. I took it to the lake, and it ran fine and cooled like nor­mal, but at idle, the temp would start to rise un­less I ac­cel­er­ated to cruis­ing speed. I’m guess­ing I may have over­heated the impeller and/or hous­ing by run­ning it on the hose be­fore tilt­ing the drive up. Do you know of any other rea­son why the impeller would not pump wa­ter af­ter it sits for a few days?

Also, when the boat is stored on the trailer, does it mat­ter if the out­drive is stored up in the trai­ler­ing po­si­tion or down in the on-plane po­si­tion?


Lake­land, Flor­ida


I’ll an­swer the easy ques­tion first. The boat should be stored with the drive in the down po­si­tion.

Re­gard­ing the cool­ing is­sue, a gar­den hose forces wa­ter up into the sys­tem, so it’s not sur­pris­ing that the en­gine ran cooler on the hose. In­spect the base gas­ket be­tween the gear hous­ing and the wa­ter-pump base. If you didn’t re­place that, you need to. Also, with the drive off, lift the bell hous­ing (the ac­ces­sory with the six bolts on it), and wig­gle it up and down and side to side. There’s a wa­ter tube on the port side of the bell hous­ing that goes up into the tran­som plate. Make sure it’s not kinked or does not have any holes in it.


Send ques­tions to Mick with your name and ad­dress to: boatdr@boat­ing­mag.com or The Boat Doc­tor, Boat­ing, 460 N. Or­lando Ave., Suite 200, Win­ter Park, FL 32789.

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