How are you supplying water from the garden hose to be able to say that "all's good" ?

Is it being forced through the pump by the hose pressure?

Is this a PCM/ Waukesha 351 with a Sherwood pump or some other engine/pump setup?

Have you had the pump off and maybe remounted it upside down so that it won't pump any water since the suction hose would now be hooked to the pump discharge?    It happens 

Have you looked at the impeller to see what it looks like?

So many questions.............answer em' all. 

In any case using the pressurized hose on the intake hose is a mistake, you can put too much water pressure on it and cause issues.  The best method is the "timmy T" you'll see referenced in multiple threads.  Basically you add a T to the intake hose between the hull and raw water pump, put a garden hose connector on the T, and when you turn on the hose it discharges out the bottom of hull until the engine starts and the pump picks up as much water as it needs, any excess still flows out the bottom.  2 advantages to this setup, 1st you can't apply too much pressure, 2nd you are replicating the hull in the water, if your pump won't pull with the hull in the water it won't pull in this setup either.

The pumps, as you've seen from having it apart, are simple as can be.  The causes for not working are upside down pump as people mentioned above, not sure what your OMC pump looks like but is a common problem on the 351's, or air leak on the suction side, which you say you've checked carefully, or a bad impeller.  If you don't want to open up the pump housing again maybe just remove the pump and see if you can turn it by hand in the proper direction, should turn relatively hard but steadily, if anything feels funky open it up to check the impeller.

Geeze Louise!

Unhook the intake hose from the raw water pump and drop boat into water, staying on trailer...(boat won't sink)

If water comes up through the intake hose, then the culprit is the next item in line-the pump.

Which is probably blocked.....

Definitely not rocket science.  You have either an air leak, or a bad impeller.  Certainly seems to me it's an air leak.  I wish someone was near you that could donate a pump to simply get you going, though I don't know how much bracket modification you'd need to mount a Sherwood pump.

It's only a UPS truck ride away 

Len you mentioned lack of clearance for a crank driven pump.............how much room do you have before things start hitting each other?

  

Maybe he's got an extra original  gas cap hangin' around 

After all, why was the pump impeller replaced to begin with?

It won't hurt anything and you'll be able to tell if you have water flowing. 

It'll fill up the engine and the water will mix with the water going to the manifolds, just like having an open thermostat in the system.

No fair forcing it through with hose pressure, hook the suction to a 5 gallon bucket with a hose feeding the bucket and watch the water come out the exhaust 

Den, I really suggest you stop launching the boat to test it, keep it on the trailer and either use the T setup I described earlier or the bucket method that Ken mentioned.  That way you really can see what's going on, is any water at all flowing.  For example, testing on the trailer you can remove the discharge hose from the pump (or other end from the oil cooler) and start it up, see if the pump is sucking up and discharging water.  If you prove that out you'll know to look downstream, if the pump isn't pumping then you don't need to worry about anything but the pump.

DenDen wrote: At this point, I can just blame the exhaust manifolds. They are the really old style. I will try to post some pictures of everything soon.

DenDen wrote: As I mentioned before, we did do the bucket test. And the pump is able to draw water from the bucket . It does seem to be an intake problem.

2 quotes above from yesterday.............Make up your mind will ya' 

How about before you put it in the pond again, you leave the suction hose hooked to the intake grate, remove it from the back of the pump and hook your garden hose into the suction hose for a backflush of the hose and the suction grate.

Only one picture in the diary

Here's the easiest way to post pictures  Watch the video at about 1/2 speed 

KENO wrote: Most anybody can post pictures these days even from a phone if they follow the directions below Steps 1-9 and watch the Youtube video in the link. KENO wrote: Mpost wrote: 75 Tique wrote: Per Ken's request/suggestion, and per Ken's efforts in finding a relatively easy way to post photos, here is a step by step process. 1.  Have photos you want to post in your phone gallery or on your computer. 2.  Open website imgbb.com (no need to sign in, sign up, or register unless you want to) 3. click or tap on "select images to upload" 4. Go to your gallery or computer and select photo(s) (Leave autodelete option on "dont delete") 5. click or tap "Upload" 6.  In the "Embed codes" box, scroll to and select  "BBCode full linked" 7. in the box at the bottom of the page where the photo URL shows up,  tap or click "copy" 8. Open your CCF reply and tap and paste or click and paste. 9. Voila, its there. (Note: it wont show up until you view preview or post it) I suppose 8 steps sounds like a lot, but its mostly quick easy point and clicks (or taps)  Goes quickly and easily.  Give it a try. Added this here so it is sticky or pinned  And added this link to the You Tube video that Larry made so there are written instructions and a video showing how to do it. https://youtu.be/0UYbzewyjXw" rel="nofollow - https://youtu.be/0UYbzewyjXw Written and video instructions all in one spot  Good idea Marty

I think you do   

So if I got this right, you think you can't get any flow through the exhaust manifolds, but you're gonna put the boat in the water and drive it around or maybe just sit there and watch temperatures while you cook your exhaust hoses if there's no flow.  .

There's a port that always provides flow

There's not been much mention of the thermostat housing, just the thermostat itself.

Den, you can see that we don't want you to give up, go a few more rounds!!!

Did you ever disconnect the hose at the oil cooler, leave it connected to the RWP, and start the engine?  If you got an instant fountain out of the hose you'd make a great case for your downstream investigation of thermostat and manifolds, but if you get a weak output or takes a while to get anything you'd know your problem was still the pump.  I know the success with the bucket test might lead you to think the pump is fine, but it leads me to think the downstream flow is fine, or at least sufficient for now.

The reason I keep saying to run it on the trailer, not in the water, is you get the whole picture.  Is it drawing water from bucket or hose T?  Yes, from bucket.  Is water flowing out one or both exhaust pipes?  I haven't seen a mention of this.  If it is sucking from the bucket ok, then put your garden hose in the bucket to keep filling it, let the engine run, observe flow out the pipes, check temp as it keeps running at maybe 1000 rpm.  Would tell you more of the story.  Maybe you've done all this, just still trying to understand the flow issue.

I think DenDen is pretty happy right about now.

We had a conversation this afternoon about his priming issues and the routing of his suction hose from the hull intake to the pump suction.

The way it was run, when the boat was turned off the line could drain completely when he took it out of the water.

Most CC's of that era with a PCM engine had a loop seal formed between the pump and the suction grate because the line looped up over the top of the transmission cooler then from the cooler it dropped into the bilge and ran up to the pump. Once that line got water in it, it stayed at least partially full all season unless you did something like disconnect the line and drain it.

That makes it a lot easier for the pump to get a prime when you start the engine.

He looped the hose upward over the rear engine mount and now he's got a loop seal.

He ran the boat this afternoon out on the lake. His words were "ran flawlessly, never heated up at all"

He's having technical difficulties trying to post a picture and video, so he asked me to post them.

Here's a picture of the newly arranged hose.

He now knows everything runs good and hopefully his loop seal makes the pump prime a lot easier every time.

    for DenDen for sticking with it.

We'll let him fill in whatever else there is.

PS still working on posting the video  Edit .........the video was really fuzzy, so I didn't post a link.

That's great news!  Nicely done Den for being willing to try stuff and listening to advice, and to Ken for the simple fix.  I've never heard the expression loop seal before, but I get it.  What is new to me is every other boat I've dealt with sucked water easily even from an empty raw water pickup so not sure why this one is harder to prime, maybe just the different style pump.

Ken, have you thought about setting up a 1-900-ASK-KENO line, you could bill by the minute like a psychic.

Let's wait though for Dennis to say it's "fixed" and keeps a prime 

You had a line that stayed full from the high point above the transmission to the pump suction even when the boat was out of the water.

Like I said earlier

KENO wrote: Typical CCF group effort

Your last review of what was done and the pictures were what helped a whole bunch.

After the winter rebuild, go for the high loop over the transmission 

I think Dennis's pump has a hard time priming itself for whatever reason and the loop helps him a lot. 

I'd say that normally for most of us, the hose routing just helps things prime easier and isn't absolutely necessary, but it makes the pumps life easier by keeping the impeller submerged for the next start

Glad to hear you are enjoying the boat now!  I know nothing about a Chevy 307, they certainly used a variety of engines in the earlier years.  No idea what you have on for a prop but I'm guessing you could find 300-400 rpm and a bit more speed with a new prop.

It's 13 inch diameter by13 inch pitch

So it's an Ellis 13x13 RH with some cup.  I don't think Ellis is still in business.

"Modern" CNC machined props improve performance, it can be pretty significant.  The trick is finding the right prop to match the boat, and there is tremendous knowledge here on that subject.  Someone will know how to match a prop to a 307 powered '73 SW 18.  I took a quick look and I think that engine was rated at 235 or 245 HP.

Then again for general lake cruising it's a question of whether that performance gain is worthwhile to you, spending maybe $400 on a prop to gain a few mph.

They came about because GM was selling 327 blocks with 283 crankshafts in them to make the 302 combination which was a very high RPM performance engine.  Not big on torque though.

The leftover 283 blocks had 327 crankshafts installed and the longer stroke made the 307.  Small bore long stroke make a nice high torque small block for its size but they were not high horsepower.  GM only sold them with a 2 bbl carb.  Turning a 13x13 prop that might be the best a good running 307 can offer.  The larger 350 and 351 engines only turned maybe 44-4800 with that prop.

The 307's in good shape got good MPG and ran well, just don't race a 350.

If you want a prop suggestion.............Acme 542  13x11.5

I'd do whatever you're gonna do like stringers, floor and get it all back together and running before thinking about another prop though.

My Malibu had the bone stock GM 350 260 HP, I acquired all the parts to build that into a 383 including AFR heads but the dang 350 ran so well and never gave me any trouble so I never did that engine swap.

Your prop is working well if you're getting 40 MPH at 4000 RPM and they're both accurate readings.

An Acme will probably pick you up some noticeable acceleration and have not much affect at all on top speed.

It may be the same plus or minus a little bit.

You won't pick up a magic 5 MPH

People with these glowing reports of big speed gains were replacing a prop that should have been in the junk pile or was totally mismatched to the boat to begin with.

I agree with Ken's post.  I saw firsthand how much a new prop changed my boat's performance, but it was more a matter of overall performance for skiing and holeshot etc.  Depending on your current prop you may gain a few mph, may not.

The old rule of thumb was you need around 12-14 HP gain to gain 1 mph.  Obviously so many other variables, inboard vs. I/O vs. jet, size and hull type, many more.  But it's a decent way to look at things when you want more speed.  If you go from the 225-235 HP you have now to an engine with 300 HP, you might get a 5-7 mph gain on top end.  That would put you into the mid-high 40's, probably not 50 on that hull.

45 in a SW 18 is pretty fast!  I'm all in favor of your idea to repower with something spicier than you have now.  Yes it's expensive, but we do stuff to our boats that make us smile.