No water going to HX

[Porchhound]

I read it but didn't make that connection. Thanks.

[KWKloeber]

I'm thinking I didn't get a prime after I replaced the impeller. Hope that doesn't mean the pump is getting weak, but it runs fine now.

Dave, "weak" - comes down to the impeller not sealing well because either (1) it's worn, (2) the pump body is worn, or (3) a dry impeller.

The pump is self-priming to a point but as I said before even if below the waterline there can be an airlock.  What I didn't say in my post is that lubing the impeller does more than keep it from burning up.  The lube seals the air leaking past a dry impeller so that it can draw a vacuum.  I installed a 2-inch pump that drew only 7 inches of vacuum (8 feet of water.)  After the seals were whetted it consistently draws 25 inches vacuum (28 feet of water.)  The same thing happens with your little 1/2" pump.

It also might not pump well if the impeller is intact yet worn.  It can be supple and the fins make contact with the cam but (depending on how many hours) the impeller faces can be worn and seal poorly.  A worn DRY impeller has that much more difficulty drawing a vacuum.  I always recommend a new impeller well before it appears necessary -- it's cheap insurance in the big picture of boat costs.

The pump body or cover plate can also be worn (the bronze body is harder than the brass cover but both can wear.)  The depth of the pump water cavity is critical -- too much wear and it doesn't matter how good the o-ring or gasket is or how flat the cover is.  Wear in the body is like using too thick a gasket or o-ring.  The impeller doesn't seal like a new pump.

Use genuine impellers.  There was a report by a member who bought an Amazon knockoff and it did not prime -- probably the thickness of the impeller was "off" a bit and sealed poorly against the pump body.

[KWKloeber]

I used the stay cool pump kit that was onboard my C34 M25 engine (Oberdorfer pump).

I'm still having problems with my raw water system moving water out the exhaust although it did work again for awhile, one time. Once I shut the engine down and removed the strainer for inspection and cleaning it wouldn't pump water to the impeller the next time I started it.

I have made certain my thru hull, strainer, and  inlet hose to pump were clear (yes, Stu I got a mouthful of tasty marina water!) I lubed the impeller and squirted dawn dish soap into the plug hole, but no bueno. I also blew through the hose to the HX and had some resistance, but no blockage. I got a great list of things that may be the problem from KW, but some of those pump and impeller housing issues are difficult to check out without replacing the pump and housing.

The photo is a before I cleaned up the housing cover.  I lightly sanded the cover on a flat surface (220 grit) and then used sandpaper to remove the old gasket from the impeller housing frame.

Which leads me to question the impeller/gasket kit I used. I have a second kit also from Stay Cool Pumps.

I don't want to go out until I know exactly what the problem is, and that I can consistently start and run my engine when I need it.

Dave

Draining the strainer and hose may have introduced another airlock that the impeller could not overcome to prime.  This is just a guess but if the pump/impeller was wet, possibly the dishsoap was thinned and did not effectively seal the impeller (air leakage not creating a vacuum vs a dry pump.)  Who knows??

(1) I REPEAT DO NOT use any but genuine impellers AND GASKETS/O-RINGS by the pump manufacturer, whether Oberdorfer or Sherwood.  (Stay Cool is one knockoff that has been a problem.)

(2) It can be dangerous (seriously, I mean it) to take at face value that a PO had followed good or accepted practice, or knew any more, or has done anything better than you can to maintain a boat or its systems!!!

Sanding the face of the pump body (depending of course on how aggressively) will alter the depth of the water chamber and alter how the impeller seals and can increase subsequent wear on the chamber and cover (so can using a non-OEM gasket.)  Avoid sanding that unless absolutely necessary -- apply SuperLube Gel (ptfe) to help keep the gasket from seizing.  IMO SLG vs dishsoap is a better lube because it's not water-soluble and so will hang out a bit longer on the back of the water chamber.  There's a cover available that uses an o-ring (like the current "Ob N202" pumps) instead of the paper gasket. 

Also SLG the impeller hub/shaft to help prevent the impeller hub from seizing (especially in salt) on the flat  If you pull the shaft to R&R the impeller (some say it's easier ) then SLG the tip of the shaft so it slides past w/o knicking the two rubber lip seals.

If your setup is such that you can "rod" the valve/thru hull to assure that you have nothing blocking it that's an option.  It's simple to set up that configuration on our 30s so that it's easy to "rod" it but admittedly I don't know about on the 34.

PS: Remove and deep-six the C-clip that holds the impeller onto the shaft -- don't use it when you replace w/ a new Ob impeller. The Wiki engine cooling section tells why.

-Ken

[Ron Hill]

Porch : How was the gasket (the square "O" ring) that fits in the strainer bowl.  It just might be the source of your "air leak" !!

A thought

[Porchhound]

The mechanic inspected the O-ring gasket and said it looked fine. I was a little shy in hand tightening the strainer, he thought, so he went a 1/4 turn past that. Because it lies perpendicular to the thru hull plumbing, an air bubble seems to never go away.

As of this writing, the exhaust flow looks good and the engine temp is staying at around 145 (checked with a FLIR gun). I took a 7sec video of the flow at 1200RPM but I don't know if videos can be posted on here. Some sites prohibit them.

[KWKloeber]

The mechanic inspected the O-ring gasket and said it looked fine. I was a little shy in hand tightening the strainer, he thought, so he went a 1/4 turn past that. Because it lies perpendicular to the thru hull plumbing, an air bubble seems to never go away.

As of this writing, the exhaust flow looks good and the engine temp is staying at around 145 (checked with a FLIR gun). I took a 7sec video of the flow at 1200RPM but I don't know if videos can be posted on here. Some sites prohibit them.

OK question where are you?   Cold seawater? 
Does she have a thermostat installed?  145 is too low  -- and unlikely w/ a working 160 TStat and a 2" Hx.

[Stu Jackson]

1200 rpm will get you nowhere.  You need to get to cruising rpm for at least 5 minutes.  My temp gets up to 180 (with a 180 thermostat) only after i've left the slip and am moving away.

[Porchhound]

Cold seawater. I didn't check the thermostat. The surveyor noted 155deg at the thermostat housing, and that was late last October. I just replaced the battery on my heat gun so I'll take a reading in the AM.

[Porchhound]

We're taking her out tomorrow (fingers crossed) so I'll be able to get a realistic read on her. I discovered a bad ground for the Temp gauge and RPM. I should get more precise readings now.

[Porchhound]

Good water flow this AM. My temp gauge died about twenty min out of the marina but FLIR directed at thermostat housing indicated 188 deg after we'd been motoring for about thirty min and stayed at that temp.

On a buoy now trying to find out the electrical issue with the temp gauge. I also noticed, upon pulling the cockpit control panel, a hot spot on my tach.

[Ron Hill]

Porch : Look at the wire attachment to the sender on the thermostat - on the engine!!  It's more apt to be "off" rather than at the instrument!!

A thought

[Porchhound]

I checked the connection and it seems to be tight. For some reason the PO ran a ground wire from the engine to the body of the sensors and attached it with a hose clamp, which makes no sense to me in that the sensor threads into the block directly. Any guesses why the tach has that hot spot?

[Porchhound]

It was working yesterday perfectly and was installed in 2019. The ground wire is a mystery to me.

[Jon W]

The hotspot is from the incandescent light bulb originally installed by the factory to light up the gauge. Some of us have replaced the incandescent bulbs with LED bulbs.

[KWKloeber]

Dave

The TStat bond that I supply with new harnesses.

Think about -
What's behind the burn spot?
Why does it make sense to separately bond the TStat cap?

The gauge troubleshooting guide is on the Wiki and the steps will determine if the gauge or the wiring is faulty (the temp gauge steps have also been discussed on here and are in the archives.)