Thread: 95 mariner 150 cooling water

I followed what the videos said, rotate clockwise while pushing down on housing.

Originally Posted by cre73

I followed what the videos said, rotate clockwise while pushing down on housing.

Glad you watched a video and bent them the correct way.

It doesn't matter. The only time it would matter is if you removed your old impeller and decided to re-install it. At that point, you would want it to go back on with the same side down (or up) so that you don't reverse the direction that it had set to. To do so would accelerate and enhance the splitting of the rubber where it had normally been compressed but now is being stretched. Many designs only allow the impeller to go on with one side down. That's what the engineers are trying to prevent with this design.

As for turning clockwise only and never reversing. I'll use the 9.8 mercury water pump as an example. It's pump body is a bit different in that the cup is part of the lower housing and the top is merely a cover. Once you install the impeller, you can view how the impeller is contorted as it rotates. a simple twist of the driveshaft in the opposite direction will allow the viewer to see that the impeller simply contorts to the opposite direction. While it is true that the pump body base is designed to only pump with the impeller spinning in one direction, the impeller will contort to either. Years ago while examining this myth, I purposely set the impeller in with a reverse orientation. A slow steady twist of the driveshaft allowed the impeller to remain oriented. But put it in water pull the crank rope and it would instantly correct itself and begin pumping water.

In fact, while going through Mercury Marine training. You are instructed to place the outboard (or inboard/outboard) lower unit in forward gear before removal. Following the replacement of the impeller, the lower unit is to be manually inspected for a positive forward gear before install. To align the driveshaft with the corresponding crankshaft (or upper drive gear), you are to rotate the prop backwards (counter clockwise). This action will rotate the driveshaft backwards (and the impeller). The rotation will allow for spline alignment and engagement. With one revolution of the driveshaft in a clockwise manner, the impeller reorients to the correct pattern.

This is not the first that I've heard of the impeller myth. But With 28yrs of experience and untold thousands of impeller replacements, I can assure you. It's a myth. Now as to the pinching of the terminal ends of the impeller by not completely seating the housing before running the hardware down, that's a real deal. I've seen several vane tips locked down between the upper and lower housings.

Sliderman , Is this true for all Outboards ?? RR

I have yet to see an impeller that won't reorient.

Not that I would recommend doing this as it was a learned art. But as part of a diagnostic procedure, I remove the spark plugs in preparing to take compression tests. While the plugs are out, I rotate the flywheel in a clockwise manner and judge the amount of resistance felt. If (judging by my experience) it seems to be on the light side, I will rotate the flywheel counter-clockwise. If I don't detect the feel of the impeller reorienting, it is a safe bet that the impeller has aged and set in a spiral and is in need of replacement. If I detect a very high amount of resistance as it is reorienting, the rubber has most likely stiffened and has splits or cracks. Different size impellers and different designs (high pressure/low volume vs. high volume/low pressure) have a varying amount of resistance when healthy and when failing. A healthy impeller will have a certain feel as it reorients inside the cup. Obviously, this is not definitive enough to declare an impeller good or bad. But I have found that it is an accurate gauge of what I'm about to see during a visual inspection of the impeller.
I say all of that to make a point. If it was truly critical that a new impeller was not reverse oriented, there would be a high amount of failures based upon this single issue. And that's just not the case. Far from it. Which brings me to how this became topic. When giving advice about installing an impeller, I do state to rotate the driveshaft in a clockwise manner while pushing down on the water pump housing to simplify instruction. (It corresponds with other instruction) But I see no need to complicate or imply doom if it is installed in a counter clockwise fashion. There are more important things to be cautious of in this repair procedure.