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blackacre

Low Water Pressure Yamaha F150

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I have a Yamaha F150 on a 2200V. Normally I get a reading of about 20 PSI at cruising speed on an analog Yamaha water pressure gauge. Recently, I am only getting a reading of about 10 PSI at cruising or WOT.

Thought I would start with replacing the impeller but is their anything else I should be looking at?

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You didn't mention the year of engine and hours but I would suggest before replacing impeller you check the hose running forward to the gauge for an obstruction first. My experience was that was a likely culprit or at least up here where we have the goo as opposed to mostly sand bottom.

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There are a few I can think of but the big ones are the tube as Triplec said, the impeller, and the poppet if it has not been cleaned/replaced. Also keep in mind as the water temps go up the pressure tends to go down.

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You didn't mention the year of engine and hours but I would suggest before replacing impeller you check the hose running forward to the gauge for an obstruction first. My experience was that was a likely culprit or at least up here where we have the goo as opposed to mostly sand bottom.

It's a 2004 with 135 hours on it. I've actually been working on it today. Impeller has been replaced along with the base plate and O-rings. Everything was in pretty good conditions from what I can see.

However, not sure if it is related to this issue but surprisingly the thermostat was stuck open when I inspected it. So new thermostat and 4 new spark plugs are now installed. Spark plugs were pretty fouled looking, probably because of the faulty thermostat. I'm surprised I had not noticed any issues with the motor running rough or making oil.

Still have to do the oil change and lower unit fluid. I will also be installing new fuel and oil filters.

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There are a few I can think of but the big ones are the tube as Triplec said, the impeller, and the poppet if it has not been cleaned/replaced. Also keep in mind as the water temps go up the pressure tends to go down.

What's the best way to inspect the water pressure tube? I'll go ahead and check the poppet valve as well.

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I found when the water temps start to rise, the water pressure goes down. I would always see around 20 in the winter and down to 10 in the summer. My ***umption is the poppit valve is open in the summer, and not in the winter. Not sure if an F150 has a poppit valve, this was the case on the 07'200 vmax I had.

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My experience is that the stainless wear plate under the impeller must be smooth with no grooves.  Damage on that wear plate significantly effect the performance of the waterpump.

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On 7/3/2018 at 5:15 PM, pbandjga said:

Dis you ever figure out what was causing the problem? Mine is doing something similar

Yes, I did get it figured it out. Went ahead and did a full 100 hour service. Ordered my parts from SIM Yamaha.

To address the low water pressure reading, I replaced the impeller. The impeller was actually in good shape but replaced it in any case. I also replaced the thermostat. Thermostat was in bad shape, and was likely not opening up correctly. 

After doing the above my F150 was running as good as new.

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