470 overheat (?) troubleshooting

[nola mike]

So this year prior to putting the boat in the water I did some outdrive maintenance. Replaced the water hose, trim senders, ujoints, bellows, shift cable. Pressure tested the drive and had an upper seal leak. Replaced them, speedi-sleeved the grooved drive shaft. Pressure tested again, now had a leak at the shift shaft seal. I swapped the gear housing with another that I had--I had less than 10 hours on this unit since replacing the impeller 2 years ago, and I didn't check the impeller prior to reassembly this time around.

Since getting on the water, the gauge has been reading hotter than usual (160 v. 145-150). Only under load, >3300 rpm, prolonged running.

1. I checked the new water hose, doesn't look kinked. Anything else I could have screwed up with that?
2. I just removed and cleaned the heat exchanger. Hadn't done that in a loooong time. It looked pretty good. I'd be surprised if that was the issue.
3. Pulled and tested the t stat. It was as open at 182' as it was at 212' (or really close). Not sure if it's opening all the way though? Pic below.
4. Replaced the reservoir/exhaust mani gasket. I noticed some coolant residue around the gasket. The reservoir and manifold looked pristine, surfaces flat.

What I haven't done yet:
1. Replaced the impeller. I'm tired of pulling the damn drive. I'll do it, but don't feel like it.
2. Verified that I'm actually overheating. I have a radiator cap with a built in gauge, and an IR gun. I haven't been able to get back on the water to check them out. Up to 210' is normal per the book.
3. Checked the impeller output. This looks difficult and imprecise enough that I'm not sure it's worth doing. I can run all day at 3k rpm and be fine. My gut tells me that an impeller problem should show up under less stress than what I'm seeing, but i don't know if that's true.

 

[stonyloam]

Mike, that is where it is supposed to run, it should have a 165 F thermostat. I would check to make sure that your gauges are reading correctly and if they are, you are OK. I THINK “normal” operating range is 160-200.

 

[nola mike]

The manual says 210'. Concerns are that the temp on the gauge has always been 145-150 max, maybe a touch higher when skiing. It's definitely reading higher than normal when under load. I'm sure the gauge is and has always been off, but it's always been consistent. Does that t-stat look wide open? I wish I had calibrated my actual temps to my gauge long ago...
Obviously don't want my princess of a motor to be too hot, she doesn't like that.

 

[nola mike]

Finally got out today, went 34 miles. Had a hard time getting the gauge back up to 160, riding 33-3400 rpm in a lightly loaded boat on a calm day. A few long 37-3800 rpm runs got it close though. Immediately put it in idle and checked temps. The mechanical gauge reading is below, might have cooled 5 or 10' Max by the time I snapped the pic. IR temps were all over the place. Even right at the tstat housing I got values ranging from 180-215, within inches of each other, and the reservoir itself fluctuated a good bit as well. So not sure what to make of all this. I think I'm ok, and I'm getting tired of chasing problems and doing maintenance. Ordered a complete impeller kit for the other gear housing, so that will be ready to go for the off season (actually, I'll probably just leave it for until I replace the drive to keep it from getting a set).

 

[stonyloam]

If your temperature is holding steady, you should be OK. If it keeps going up then you could have a problem.

 

[nola mike]

Still looking like around 160 under heavy load, less when I slow down. Might not be optimal, but I don't think it's way out of line at this point. Starting to get a bouncing tach and other gauges. Wondering if I have a bad ground. Have to think about whether that would give me high or low readings.