Can an impeller vapor lock?

Just wondering. Can an impeller get air in it and vapor lock even when under water to the correct level, (not on muffs). And if so what would cause this?

Re: Can an impeller vapor lock?

NO. WHY? More info.

Re: Can an impeller vapor lock?

Long story short.......Johnson 1977, 75 hp, 2 stroke, ob. No pissing.....quickly overheats....(runs fine otherwise....idles/planes/everything...for 5 mins until overheating occurs and I shut down....

Testing:

Lower end removed.....impeller fine, water tube inserted correcty into pickup, key in place (impeller turns when shaft rorated by hand), no obstructions in screen area. Hose connected to water tube (lower end still removed) and water flows through pisser and engine just fine (pisser installed just before t-stat). Im out of things to check?

Re: Can an impeller vapor lock?

Check your thermostats. Pull the thermostat and fire the motor up. Water should come gushing out. That could also blow out any debris thats in there too. Also check the tell tale too and make sure it's not clogged. A clogged tell tale won't cause overheating, but it's nice to have it.

Re: Can an impeller vapor lock?

Well yes actually impellers/water pumps can fail when air is introduced. They make good water pumps, not so good air/water pumps

One of the reasons you must keep the t stat and valve installed on say the Super Quiet style Big Twins for one. Air/exhaust will get into the pump and render it useless.

Things that are possible in your situation.

The water tube is getting pinched in the grommet on top of the impeller housing. Worn housing/plate. Defective impeller.

Before intstalling the lower unit on the motor, drop it into a bucket of water and chuck up the drive shaft and spin her up. Does she pump water out of the water line? If it does, you issue has to either be at the water line/impeller housing connection as you said the cooling circuit is free of debris.

Re: Can an impeller vapor lock?

A impeller cannot air/vapor air lock but in can starve if water that introduced to it is full of air such as dirty bottom,gouge in fiberglass, bottom paint interrupting flow(hair puller)or engine mounted to high(4 new 200 hp blown:facepalm

Re: Can an impeller vapor lock?

Any tips on how to chuck up the shaft......Do I need a really big drill, or can I adapt my 1/2 inch somehow? Maybe just tape the 2 together??

FYI...This is a stinger like yours faztbullet......I notice yours is a project too.

Re: Can an impeller vapor lock?

Does it "P" good at idle in water???

Re: Can an impeller vapor lock?

Just a stupid question but are the water inlets (on lower half of outdrive in the front) free from obstruction or even partially blocked?

Re: Can an impeller vapor lock?

Thanks for all the suggestions guys.......still working on this......to answer your questions:

1) No pee at idle or wot...not even a drop
2) strainers at LU are completely clear

A bit of history in case this helps: Everything was running fine but I had never replaced the impeller and didnt have a telltale (I bought the boat a couple years ago). I opened it up and replaced the impeller (which looked fine btw) and all components in kit (no housing available, but the old one looked ok). Then I installed a telltale right before the t-stat. Took her out and everything went great.....Telltate had a strong stream at idle and at wot.....boat ran great...got up on plane and everything......Then after a few minutes of driving, I shut down at the dock for a little.........I fired it back up and no pisser....not even a drop.....Ran it for a couple minutes anyway, thinking maybe id force some water over the intake at high speed and get things going again, but no luck....no pee still......after a couple minutes got the high temp warning sound and shut down.

My first suspicion is my own work, so back at home I dropped th LU, expecting to see a shot impellor or something that broke, but nothing....Everything was exactly as I left it....Impeller good (not spinning free from spines), key in place, water tube inserted in pickup tube and seal not crushed, strainers clear. More confused than ever.

Thats why Im thinking its something I cant see like air getting in somewhere, or maybe a tiny metal shaving from drilling the telltale hole gumming up the works....I still need to chuck up the shaft with the LU in a bucket and make sure water pumps, but Im not sure how to attach my drill......Still working on it and will keep you posted.

Keep the suggestions coming...I need the pros on this one.......Thanks guys!

Re: Can an impeller vapor lock?

At idle the entire pump assembly should be underwater. There's no air down there and any air trapped in the impeller housing should be quickly expelled.

"Hose connected to water tube (lower end still removed) and water flows through pisser and engine just fine (pisser installed just before t-stat)."

Assume you mean a hose connected to your household water supply? Usual household water pressure is in the 30-60 (sometimes higher) psi range. I believe that is significantly higher than the pressure output of your impeller/pump combo. Could you have an obstruction up above the lower end of the water tube? An obstruction that the household water pressure will blow by but the water pumped by the motor will not?

How about using the hose to reverse the normal flow pattern? Shoot it into the inlet to the thermostat housing and through the tell-tale in an attempt to blow out anything that might be stuck in the passages?

Another possibility that I encountered w/my motor. Impeller looked good. Decided to replace it anyways. New impeller significantly "stiffer" than old impeller. Worked fine when "wimpy" impeller was replaced.

Re: Can an impeller vapor lock?

Thanks for the ideas.......Have to transport my boat to a water supply for more testing. Unfortuantely Im working in a parking lot and not a garage. But you are correct (I used a garden hose...household supply, not sure of the pressure). One more thing I did try though, Unplugged the pisser restrictor and blew air into the telltale tube (with my mouth), and felt air coming out the L U pickup tube. Will try again with water. So I feel that it may be clogged, but not 100%. I was under the assumption that a partial restriction would slow down my cooling water but not stop it completely, but that is starting to seem more likely. I hope not because that sounds like a lot harder to resolve.

Re: Can an impeller vapor lock?

If you have access to an air compressor that puts out 125+ psi I would get a needle jet nozzle and shoot air back through the line from the thermostat side. Making sure that the line was disconnected on the LU/impeller side. This will clear any debris from the lines. Possibly a bad thermostat. Only way I know of testing them is in a bowl of boiling water to see if they open from a closed position. Other than what the others have suggested I'm stumped.

Re: Can an impeller vapor lock?

Latest update on testing.......OK, I took the boat to a water supply tonight.....L U is still off, I took off the T-Stat cover and removed the tstat and relief plugs.....Hooked up the garden hose to the LU water tube and water pours out the t stat hole....Put the hose in the tstat hole and water pours out the water tube at the lower end.....Then put the tstat cover on without the tstat in and sent water up the water tube at the lower end.....water poured out the exhaust at the LU.....Pretty sure there is no blockage anywhere in the water channels.

However, I did see sand in the thermostat and the 2 relief valves next to the thermostat, which tells me maybe there was more sand in the engine which I blew out during one of my water tests. Who Knows? (BTW....I put the tstat in a pot on the stove and watched it with a laser thermometer. Opens and closes between 120 and 140 F, which I think is about right)

I guess the only thing left to do is chuck up the drive in a bucket. If that test proves good im gonna put it all back and cross my fingers? What do you guys think??

Re: Can an impeller vapor lock?

maremsk1 said:

Latest update on testing.......OK, I took the boat to a water supply tonight.....L U is still off, I took off the T-Stat cover and removed the tstat and relief plugs.....Hooked up the garden hose to the LU water tube and water pours out the t stat hole....Put the hose in the tstat hole and water pours out the water tube at the lower end.....Then put the tstat cover on without the tstat in and sent water up the water tube at the lower end.....water poured out the exhaust at the LU.....Pretty sure there is no blockage anywhere in the water channels.

However, I did see sand in the thermostat and the 2 relief valves next to the thermostat, which tells me maybe there was more sand in the engine which I blew out during one of my water tests. Who Knows? (BTW....I put the tstat in a pot on the stove and watched it with a laser thermometer. Opens and closes between 120 and 140 F, which I think is about right)

I guess the only thing left to do is chuck up the drive in a bucket. If that test proves good im gonna put it all back and cross my fingers? What do you guys think??

Click to expand...

The only other thing I can think of if everything you said above works is that you may have a build up of sand or gook somewhere in the water jacket of the head of your motor. The only way to fix that is to pull the top head piece (the piece the spark plugs screw into) and look in between the inner and outer wall of the block to see if you can see a blockage. Try fishing gently with a long zip tie to see if you can feel a blockage. If you can, tilt the engine so the pistons are facing straight down and blow water through the tube from the impeller to see if you can clear the clog. Sometimes you can build up sand in there and there's no other way to flush it out.

Re: Can an impeller vapor lock?

Another thought, based on my personal experience. Any chance the intake came out of the water during the high speed run (maybe tilt angle adjusted wrong)? This could result in the impeller running dry, or almost dry, for a short time and might compromise its subsequent performance without actually destroying it.

Why not cover all the bases and replace the impeller while you have the LU down?

Re: Can an impeller vapor lock?

Hmmm.....possibly......I'll replace the impeller (the whole kit actually) before I test it in the water again anyway......Thanks, and I'll let you guys know what happens.....Thanks again