351 overheating

Jim,
It sounds like you did the needed checking but go over your hoses again. No screwdriver on the hose clamps. You can't get enough torque. Use a nut driver or socket. Overheating at idle indicates sucking air someplace but it could also be a blockage. Check for bits of old impeller at the T stat and at the trans cooler. Was the old impeller busted up? Do use an OEM impeller and not one of the aftermarket ones like Sierra. There are known problems with them. Sucking from the bucket is the best method for troubleshooting since problems aren't masked by direct pressure from the hose. You did find all the missing plugs correct?

Welcome to CCfan. We always ask for pictures so when you get the heat issue fixed, post some!

Pretty unlikely but sounds like it wouldn't hurt to check the actual intake. Maybe someone bottom painted over it or something.

FootFever78 wrote: Update: Checked the strainer and hose from the intake. At idle with a garden hose pushed into the intake end of the hose, there were no bubbles in the strainer. When revving, the bubbles began appearing in the strainer. My next move is to bypass the strainer all-together. The intake hose also looks suspect so I'll be replacing that and all other hoses asap. The intake looks clean now.   Will provide another update once able to bypass the strainer and test. This sucker really wants to run. Hopefully I can replace the strainer if needed and/or o-ring(s) and be off the races.

Try running the intake hose and a garden hose into a bucket instead of hooking it up directly to the garden hose. When hooked up directly, the garden hose will supply enough water at idle, but as the pump speeds up it will either pull air or collapse the hose. Using a bucket is much more of a real world simulation to see how much the pump pulls on its own without water being force-fed into the pump.

I had strainer issues last year. My Oring was not sealing.   I filled the Oring slot with silicone, Wiped the clear cover with a thin film of Vaseline and bolted it together and let it cure. It works now and the cover is still removable, but now it seals on silicone rather than the O ring.   If I had a spare O ring on hand I would have used it.
On torqueing the hose clamps, the intake hose is large and stiff, nearly impossible to clamp it cold. Warm the engine and the hose if possible and tighten it while warm and you will get a good clamp. If you don't have a good hot sun and a warm engine to work with a hair dryer can heat the hose up pretty quickly. You will be surprised how easy it is to clamp while warm, it gets more flexible.

spiralhelix wrote: fwiw, when we had water pump issues, a buddy just replaced all my intake lines from the through hull to the t-stat housing with 1" I.D. clear braided vinyl tubing. Every time i start the boat, first thing i look at is that water is flowing from the through hull intake, through the strainer, trans cooler, RWP, to the t-stat. piece of mind for $20.

Careful - it may collapse. Wire reinforced has been mentioned many times here.as the recommended replacement

Braided clear vinyl and wire reinforced rubber are not the same.

Bubbles off the hose are because the house pressure isn't enough to supply a revving RWP, not idicative of any air leak.

Waternut wrote: Did you ever figure out this problem? The clear braided hose is usually pretty stiff at 1" ID. Theoretically, clear braided is really meant to assist positive pressure (inside out). Wire reinforced is meant to resist vacuum (outside in) and resist kicking. Considering the low pressure dealt with in our boats, both are plenty stiff and both resist kinking pretty well.

John,
Your stating the intended purpose of the tubing or hose is correct. You being an engineer I'm sure will also agree that the hg" vac ratings (not low pressure) of each are important before selection for suction sides of any pump.

On the suction side of the RWP, I do not suggest anyone to use the braided vinyl tubing "Joe Schmo" found I'm sure at the hardware store. On the pressure side of the RWP has issues as well. Yes, it's braided to resist pressure but it gets real soft as temperatures go up and the reason ratings are given along with temperature.

I have been having similar issues with my 83 SN. Did the same checks and all is good with the impeller, pump, t-stat, strainer o-ring etc... I pressurized the system with the garden hose and found no water leaks. Then with the bucket water test in the driveway, the RWP was pulling very strong (so the RWP is ruled out for now) yet I was still up around the 200 degree area. Then I checked the circulating pump and the pulley has a bit of wobble to it telling me that the bearings are going bad and it is struggling to take the raw water and push it through the block. Curious if I am on the right path, any thoughts?

Peter, yes it was connected to the hose on the intake side of the strainer. The strainer o-ring is brand new.

The engine was completely rebuilt with a new t-stat and impeller, but still ran both of those checks and both were good.
Another interesting fact that I have struggled to process is that the water leaking out of the strainer lid last weekend before the new o-ring was installed was too hot to touch, at the strainer. Points back to circulating pump not pushing water into the engine and heating up the water on the suction side of the RWP... May be reaching here but nothing else makes sense.

Exactly! So how could it get hot? My theory is that the circulating pump was not circulating the raw water into and out of the block. The RWP, doing all or most of the work, could not replace the hot water quick enough with raw water so the heat build up made its way upstream into the suction side... Any ideas?

Chris,
You mentioned the engine has been rebuilt. Check the routing of the plumbing to make sure it was installed properly. How about posting some pictures especially the hose around the RWP. Even though you did a bucket test, are you sure the RWP isn't installed backwards?

Update: I installed new hoses (clear with braided reinforcement) so that I could see what's happening.

I bypassed the strainer, ran a hose into a bucket full of water. Engine fired right up, ran to temperature, sucked in water no problem.

I then re-installed the strainer and put the intake hose in the bucket to run the same test, and the engine only sporadically sucked water before stopping all-together. (all of this was done in my driveway)

Figuring the strainer had a leak, I took the boat to the ramp and ran a hose from the intake to where the strainer hose normally attached to the engine (can't recall that part name). So no strainer. The boat sucked water up to the top of the hose but would not suck water consistently, not even for awhile.   Very frustrating because I thought I had it isolated to a faulty strainer.

So now I am thinking I may have smoked the impeller somewhere along the line and that it needs replaced. I'm going to check that tonight as I ran out of time yesterday (Mother's day obligations).

My question is this: Could my other water pump (not the RWP) be bad? Is there a way to test that before buying a new one?

In my mind the only way you could get hot water in the stainer, is the rwp is putting it there. That would mean you have a hose on backwards.
How would you be picking up any water to go thru the block to get heated up?
The only water intake would not being used. Instead you would be trying to push water out of the water intake thru the strainer.

Don't think so