Overheating at idle, cool as a cucumber at speed

[l008com]

Ok new problem. Even though my impeller looks fine, I have it all open so I might as well replace it anyway, it is years old.

But everywhere I look, this part is no longer made and not in stock ( 430261 )
Is there an updated part number? Is there a better way to look this up than by engine serial number? On my 34 year old engine.

 

[l008com]

Disregard my last message, I found it on boats.net so it's on its way.
So I figure I'll replace the impeller, fire up the engine with the water ear plugs on it and see if it gets hot, and then just poke around. I wonder if the exit plug is partially clogged, because I've had that happen before. Although that doesn't seem like a situation that would only be a problem at low RPMs/speed.

 

[racerone]

47-43026T is on the shelf everywhere !!!!

 

[l008com]

So how did you get that number? Also when I search West Marine, I get no results. I think that's the only boat shop around here.

 

[racerone]

Couple of clicks on a Mercury parts site.---Listed at $33.95 factory quality.

 

[l008com]

Couple of clicks on a Mercury parts site.---Listed at $33.95 factory quality.

I found my original part number on that site but I didn't see anything about a replacement number. *shrug*

 

[racerone]

Part is available all day long !!---And will be for many years.

 

[l008com]

I dont see the water pump housing seal thats on top of S/S housing. This will let exhaust to enter water pump housing.

I took a closer look today and it looks like the last person to replace this used gasket caulking or whatever it might be called. But it's peeling off so I agree I should replace it with a new, real gasket. Can you get JUST the gasket? Anyone know THAT part number?

 

[Chris1956]

Why not try the crowleymarine web site for part numbers and parts.

 

[l008com]

Ok I got the new gasket that goes between the plate and the impeller housing. I was scraping off the old one, which seemed to be some form of "liquid gasket" on top of an older real gasket. So after some scraping, I decided I'd just pull the plate off to make it easier.

Once I did that, there was all sorts of gunk under there, both on the bottom of the plate and on the lower unit. So I started scraping that off too and after a while (not right away!) it became clear that I was scraping away yet another gasket!
So is there supposed to be a gasket on the bottom side of the plate or can you skip that one? If it's needed, guess I need one more part before I reassemble!

 

[Chris1956]

The SS wearplate should have a gasket on each side. Put them on dry, and make sure to match the wearplate and housing with the correct gaskets.

 

[l008com]

Bummer. Ok one more part on order.
New, related question. The motor was in neutral when I took the lower unit off. When I turn the main drive shaft by hand, the propeller does not spin (as expected). But the rotation is not smooth. It feels pretty rough. Is that normal? If there are bearings in there somewhere, I imagine they are about the worst condition bearings possible.

 

[Chris1956]

The impeller can change the smoothness of the driveshaft turning. I would pull the impeller and then check the gearcase bearings for smoothness.

Also, some driveshafts need to be pushed down by the waterpump base and shims, to set the driveshaft bearing into it's race.

 

[Faztbullet]

That unit uses a special cut on gears that pushes driveshaft up into bearing as its upside down. Pull up while turning and should get smooth. Also the factory gasket has a orange bead of sealer on it

 

[l008com]

Hmm, neither of the replacement gaskets I got have a sealer bead on it. Is that going to be an issue?

Also I'll try lifting up and spinning next time I'm working on it, just to see. I'm hoping I can get at least another 10 years out of this 39 year old boat

 

[Faztbullet]

If replacement gaskets dont have the sealer bead just coat them with aviation sealer

 

[l008com]

Finally had a few hours to work on this again today.
I got the new gaskets on there on either side of the plate, got the new impeller and housing bolted up, the lower unit is ready to be thrown back on the boat. But I couldn't do THAT because it started raining.

I did get out there with an air compressor and try to blow some air through both ends of the water path to make sure it wasn't clogged. Meaning the hole where the water goes up through that is uncovered because the lower unit is off, and the actual spout where the water pees out the back. Air flowed through just fine, HOWEVER I did notice this big KINK in the tube!

And I tell you, the 10ish year old impeller looked basically brand new. And the motor was overheating at idle, but running cold at speed. Exactly what might happen with a kink in the hose! It needed the water pressure from higher RPMs to open up the kink and let water through!

I think this was the problem all along!
What do you think?

Assuming ya'll agree, what kind of hose is this? Is it a specific type and/or size? Looks like it's just zip tied in place so once I get the right stuff, it should be super easy to replace it and be on my way.

Also the trim piece that that hose connects to does need to be removed to get to the spark plugs, so I can see how a kink could have happened. What if I made the hose longer and put a loop in it before it went to the outlet? I can't think of any problems that would cause but best to check first.

 

[Chris1956]

A kink in the telltale hose should not cause an overheat issue, as it is not (or should not be) the only outlet for water going thru the thermostat.

I would pull the thermostat cover and make sure the passage that goes to the exhaust cover is not blocked, and the exhaust cover has flow out the midsection.

You can put a hose on the water tube in the midsection and run some water thru the block (low pressure only) and see if the thermostat openings give full flow.

 

[l008com]

Whether it's the cause of the problem or not, that kink bothers me so I'd like to replace that hose. What kind of hose is it? Should be cheap enough right?

Also where is the thermostat on my motor? I've seen videos of removing it on newer engines. Should be easy enough to pop it out and see if it's gunked up if it's still overheating with the new hose.

 

[Chris1956]

Gee, the crowleymarine site will have diagrams showing your thermostat and poppit valve.