Ran engine dry briefly - should I worry about impeller?

[isaksp00]

This is a 8HP Honda 4 stroke, BF8A, about 1993 or 94.

I bought boat/motor a few months ago, and had motor in shop (turns out PO had not used it for a few years, carb gunked up).

After I put on the boat, I wanted to make sure it would start - no point in stepping mast on 23 ft sailboat and then have to pull it right out from still bad motor.

It is not near a water supply in yard, and I had been told it is OK to run for a very short time dry. I started it, let it idle for perhaps 5 to 10 secs then shut down. The yard mechanic dressed me down - said it is very bad to run dry for even 1 sec.

So, when I launch it - assuming the water cooling seems OK (water exiting spit tube properly) should I worry about impeller damage - say, enough to have it looked at? Obviously, if there is no cooling water, I would have to do so.

Thanks.

 

[Barnacle_Bill]

Re: Ran engine dry briefly - should I worry about impeller?

I would replace the impeller. Not so much because you ran it for a few seconds whick you shouldn't do but it has sat for a couple years and they do dryrot. And you don't know when it was last replaced so play it safe and replace it.

 

[isaksp00]

Re: Ran engine dry briefly - should I worry about impeller?

Thanks for the reply!

Didn't think of the dry rot issue, given that tis has sat about 2 yrs, maybe closer to 3.

I know I can buy an impeller kit for about $30 (impeller, 2 gaskets, water seal). Is it hard to do yourself? Looks like it is in the middle of the shaft unit, so I assume it involves dropping the lower shaft. Is the housing for the impeller directly exposed at that point, so you just replace the parts? Any special techniques, such as use of any proper lubricants?

Thanks.

 

[Jake Windemere]

Re: Ran engine dry briefly - should I worry about impeller?

If the tell tale squirts water at idle you are good to go.

Run it in a large garbage can for a while to assure that the impeller won't fail soon after first started. If the impeller is dry rotted you might get a few minutes run time before the impeller vanes break.

If you run it a few times and the tell tale still squirts at idle you can wait until the pump fails or trickles water at idle.

Yes, it's bad to run the impeller dry but I will run mine for a second or two after pulling my boat from the water in freezing conditions to assure that all of the water is out of the passages. I'd rather put wear on my impeller than risk cracking or freezing internal parts.

 

[Jake Windemere]

Re: Ran engine dry briefly - should I worry about impeller?

If you do replace the impeller get a kit complete with the housing. Not only does the impeller wear but so might the mating surfaces. Here in Alaska we deal with silty water which sands away the steel in the water pump as well as the impeller.

 

[Bifflefan]

Re: Ran engine dry briefly - should I worry about impeller?

If the tell tale squirts water at idle you are good to go.

Yea, thats not ture. It may pump enough to make it pee, but not enough to keep it cool.

As stated above, replace it just because of old age.

By the way, I forgot to turn on the hose once and ran mine for about 30 seconds before remembering. I didnt have to replace mine this time, but it was brand new when I did it.

 

[isaksp00]

Re: Ran engine dry briefly - should I worry about impeller?

Thanks for all the help!

Boat launched for first time this morning (I picked a day with a rainstorm to do it). I left it tied to the dock and ran engine at idle (yes, intake was well under water) for maybe 20 mins - there was a solid stream from the pee hole (this engine has no prostate problem, at least not yet). I then ran it in fwd at maybe 1/3 throttle, for maybe 5 mins. Seemed OK. Later, when it was a bit less rainy, I motored out for about 5, maybe 10 mins to put her on the mooring. Seemed OK, and engine did not seem hot.

I think I'll watch it, and leave it for now (only about 2 1/2 months left til it has to be hauled anyway). I ordered the shop manual today, so I'm hoping I can do the new impeller kit install after season.

Is it obvious if it is running hot, by feeling the top of the head area, around plugs, etc. ?

 

[rogerwa]

Re: Ran engine dry briefly - should I worry about impeller?

You are probably ok for the rest of the season, but I would have it changed before the spring. This spring I had to rebuild the carbs on my 90A and I thought about doing the impeller but chose not to due to time constraints.

Well this past weekend I idled out of the river (1/2 mile) and started to power up and the alarm went off and the limiter kicked in, only to find no water coming from the output. I had to have my 25' pontoon towed back to my dock where I spent the next morning changing it in the water. Not fun. What was weird is that the hub of the impeller separated from the impeller. The impeller did not break up as they normally do.

If this has not been used in a number of years I think you dodged a bullet as that impeller should have busted apart on you.

 

[isaksp00]

Re: Ran engine dry briefly - should I worry about impeller?

Thanks, that is exactly what I am going to do - I just hope, once I get the shop manual, that the instructions are obvious enough. I'm handy, but no mechanic. I'll be liberal with the PB Blaster! I'll watch the output stream and try to monitor the temp of the block as best I can by feel.

Good for you that no real damage occurred, hope it was an easy (and not expensive) tow.

 

[rogerwa]

Re: Ran engine dry briefly - should I worry about impeller?

Just a case of beer..