'58 5.5 CD-15 overheats after impeller change

[kbait]

This one had been sitting for 15 yrs. Cracked coils and ignition taken care of. Barrel tested and it ran good, but little water output at low idle, better-not much at high idle (Barrel water just below exhaust port.. plenty deep). Water splashed on head boils. So I figured the impeller was toast. Pulled powerhead and dropped lower unit to change it out. Impeller had taken a bit of a set, but still looked ok. Changed it with a new one and put it back together (pin installed correctly and watertube inserted into grommet). Water tube was clear. Test run, and even less water out port in back, no matter rpm's, and overheat again. I didn't actually pull the impeller plate when apart, but it looked flat. Blew canned air in water intake and I could feel it coming through that plate, so I figure intake is clear. I usually blow air up the watertube before installing lower unit, but this one has the powerhead removed so you can't really check the flow through the powerhead through that tube.

Any ideas? I'll pull it apart tomorrow and spin the driveshaft while the L.U. is in a bucket of water and make sure it's pumping ok. Anyone know how to check the water passages in powerhead when powerhead is removed? I blew through some ports when I had it off, and nothing appeared to be blocked.

Thanks!

 

[HighTrim]

Re: '58 5.5 CD-15 overheats after impeller change

Did it have a metal impeller housing, the original? Was the vent hole open and clear? How bad was the housing itself? Any scoring? Was the plate sealed to the housing? Perhaps upper grommet is swollen?

If all else fails you could pull the head and the water passages there may give an indication of what the rest of it looks like.

Depending on the housing it has, I have had to dress the mating surface, to shorten its height, Improving water pressure. Doesn't need a lot, but it helps.

 

[nwcove]

Re: '58 5.5 CD-15 overheats after impeller change

put the powerhead back on , rig a garden hose to the water tube, and try it with low pressure!

 

[OptsyEagle]

Re: '58 5.5 CD-15 overheats after impeller change

When you take the powerhead off, make sure you have the right exhaust to powerhead gasket. The CD series has about 3 different types. If they gave you one for another model year perhaps your water flow is sealed off. I know some CD models have T-stats and some do not. If I recall yours doesn't but I am not sure. Anyway, maybe the water flows a little differently with the one with a T-stat and if you have that gasket, it might restrict ... or not, I really can't say.

You should be able to find the water entry and exit area at the bottom of the powerhead. Perhaps you can blow some compressed air in there and see if you feel it flow. Pulling the cylinder head might also shed some light on the problem.

 

[kbait]

Re: '58 5.5 CD-15 overheats after impeller change

Thanks for the replies. Since it's still all together, I'm going to pull the head and take a peek. If that's good, I'll pull the powerhead again and check out that gasket. Perhaps previous owner changed the impeller and gasket years back, used the wrong gasket, and just set it aside because it was overheating. I'll also scrutinize the impeller housing and check the vent. I'll post back w/results.

 

[kbait]

Re: '58 5.5 CD-15 overheats after impeller change

Optsy nailed it! Wrong powerhead to exhaust housing gasket. Replaced and now it's pumping/cooling nicely. Thanks!!

 

[OptsyEagle]

Re: '58 5.5 CD-15 overheats after impeller change

Glad to hear it helped. I had a dealer give me a wrong PH to exhaust gasket once, but I noticed it by the wrong part number before I used it. Never knew what kind of problems it might have created but was glad to get the right one before I put the powerhead back on.

The only other thing I could think of was perhaps a banana got stuck in there. LOL.