Speedracer29

I wouldn't rule out the transom fitting simply because I've seen some weird issues on the old 70's Pontiac motors where the divider (restrictor) plates for the water pump were left out, and resulted in an overheat condition, while everything else was textbook fine. I don't have much knowledge in hydrodynamics, but I would postulate that higher pressure and lower volume can happen simultaneously through a capillary (hose) if a restriction is causing a reduction in the size of the hose at some point before the sender..... I've been wrong before though, so hopefully a plumber or physicist reads this!

Sunny32SSR

For my own knowledge, does the drive need to be drained and removed? Just had the gear oil changed

Sydwayz

iTrader: (1)

What is your water pressure at idle?
Are both engines flowing the same amount of water out of both exhausts when idling?

Do you have fresh water flush connections in the bilge? These systems often have check ball systems in them that get gummed up with silt/debris, and cause cooling issues that are hard to pinpoint.

But the Rinda scanner. It will be the best $500 you spend on the boat, guaranteed. Just waiting 2-3 weeks to find get in, get scanned, and find out you need a $100 part (one day) in the dead middle of summer is worth the investment in your time and enjoyment. You can take the boat out on the lake with the Rinda hooked up, and monitor the sea water pressure, temperature, and exhaust manifold temperature on each side of the motor. They are worth their weight in gold IMHO.

smokin' gun

iTrader: (30)

ive seen it both ways low to no water pressure .when the boats gets on plane if you have low water pickups u still get pressure under speed
ill give you a for instance .my buddy has low water pickups on his drives motor was getting hot so he shut off that motor and ran on the other 1 coming home .as soon as we got out of no wake areas he would run the other 1 we ran up river for 20 mins never got hot cause the low water pickup forces the water to motor ..we got home pulled the pump and no blades left on the impeller ..

ballz2thewall

yes but why is the motor that is getting hot have higher water press? Because there is a restriction after the pump. The transom fitting is before the pump if there was a restriction there he wouldnt have high warer pressure

BUP

iTrader: (9)

smoking gun is correct about that fitting for the water inlet hose it can cause water flow problems and or overheating.. also make sure u r not having a water hose collapsing anywhere in the system. Also other areas water circ pump and or t-stat along with restrictions in those areas as well.

BUP

iTrader: (9)

Yes you can pull ur drive without draining the gear oil. As you pull the drive off and reinstalling it , you will lose a tad or some gear oil depending how quick you are. It comes from depressing the dribble valve assembly and from that the oil line that leads up to the gear oil reservoir. Just top off your gear lube res to full again after you reinstalled your drive.

Do not change the 160 degree t stat to 140 in any computer control engine unless you have it remapped for it. It will take longer to warm up correctly and run rich. A rich running engine will lead to problems down the road. Fouled spark plugs and washing down the cylinder walls plus wasting fuel are the first 3 issues.

Back to info about water hoses - make sure the length of your input water hose is not too long because it will put (have) a kink in it. Seen that done on repowers and caused overheating issues. Plus make sure you do not have any kinks in any cooling hoses.

Mercruiser has water volume tests & specs. Also we put clear water hoses for testing only purposes in place of the regular water hoses to look for air bubbles in the cooling system. Aerated cooling water will cause overheats as well. Air bubbles ( aerated cooling water ) can be caused by air leaks, an impeller cavitating, a bad water circ pump, bad water hoses, loose hose clamps, restrictions and so on. This test will help pin point your problem area.

Sunny32SSR

Thank you for the detailed response!

I never thought about the tstat and computer needing to be remapped. Makes perfect sense as you have to tell the computer on a car the same thing.

Aside from the boat warming up after hitting the lovely debris fields it never had an issue nor did the previous owner encounter the issue.

All hoses are stock and the impellers/housings are new. I had forgotten about the circulation pump.

Scagburner

Cory – The pressure gauges always had a little stagger but never 12 psi. The most I could recall was 3 -5 psi which I would consider as normal. I also never saw 35psi at 4k rpm but with the new Hardin pumps perhaps it’s higher now. In fact, 35 psi would probably be about what it pulled at WOT.

I also never saw the temps that you are currently seeing on the starboard side. It always stayed within normal range and the same from side to side. There are a lot of good suggestions here but I want to think you still have some restriction beyond the pump. Attached is the schematic of the cooling system. I would try to back flush each cooler independently. If small debris has pushed thru the steering, oil and fuel coolers and made it the whole way to the heat exchanger under running pressure, I doubt a garden hose has enough pressure to push it the whole way back thru everything… I would think you have particulate trapped between coolers...

Example, you back flush and the debris moves from the inlet of the oil cooler to the exit of the steering cooler. Once you start the boat, the debris moves back to the inlet of the oil cooler… Make sense?

Why don’t you haul it back up here so I can drink beer and tell you what to do while you stand on your head and try to get the hoses off all those coolers?

Sunny32SSR

And this, folks, is exactly why I bought the boat I did and love the Sunsation/OSO community.

John - Again, as usual, you bring up great points I hadn't thought through in regards to running pressure and back flushing and once again getting stuck. Makes sense why others have used air, "blowing and sucking in a back and forth fashion" (that one made me laugh), and making specific attachments to increase pressure.

It could be the pumps driving a little extra pressure but I seem to recall that at 5k-5100k pressure should be reading 32psi which is what she was reading the first time out. Also, first time out the psi was within the 3-5 marker you mention.

If the boat wasn't 200mi away I could be doing this in my driveway right now... Just be glad I'm clearing up all the debris before you make it down here. I took your fishing net request literally however it has come in the form of the low water pickups on the boat

However, I may haul it back up there just so I can drive the Bobcat!