Replaced Impeller
 

I have twin Merc 6.2s in my Formula. My left motor overheated the other day, found a shredded impeller to be the problem. Replaced the part, flushed out the broken pieces, and put everything back together. Engine seems to be running fine, but still running warmer then the right motor. Took it out today and water temp gets borderline too hot at full throttle causing the temp hi light to flicker on the gauge. Also note that left motor turns more RPM when throttles are matched. Any ideas what is causing this? My engines have only 117 hours.

When it got hot the thermostat spring could have lost its tension.Replace both thermostats and see what happens.You could also check the power steering coolers for impeller parts
Also how scored was the see water pump yours should be brass was the end plate scored really bad? As for the RPM how much and is it noticable at WOT or just mid range

How difficult are the thermostats to replace on these motors? My impeller kit included a replacement end plate. The difference in RPM is mostly during midrange, a little at WOT. Only noticed it because the RPM was pretty close between both motors before I had this issue. Does belt tension affect RPM at all?

Easy ther are two bolts holding the housing (10mm) I think I usually disonnect all hoses before I take housing off.You will need three parts the thermostat,gasket and the plastic ring you could reuse the plastic ring but the usually break tring to get them out so I don't even try.
As for the rpm mine are a little off at idle (always were) could belt tension do it,maybe the are turning a lot of stuff.Unless its more than 150 RPM I would not worry about it. Did you do both impellers?because the new one is harder to turn that might be it also.
http://www.mercruiserparts.com/Show_...at+and+Housing

You may have two gaskets one on each side of the thermostats

how hot is your motor running? temperature wise?

You probably have some impeller pieces still stuck at the front of the oil cooler.

skip the thermostat BIG Daddy and get the impellor pieces out of the cooler and she'll run fine 4 ya .did 2 of them up at the river this weekend and did'nt touch any thermostats :drink::drink::drink::drink:

X2 on this one. If all you did was "overheat" it - as opposed to "smoked the living crap out of it", your thermostats should be fine. Most times we find a few extra pieces of the old impeller in places folks didn't look. That's why it helps to try to approximately re-assemble the smoked impeller to see if you got all of the parts.

6.2s don't have oil coolers unless he added them.As for the thermostat I had some see grass block my pickup and engine went up to 220 for a second or two.I changed the impeller as it had run dry.They are cheap and easy so why take a chance.That motor ran 180-185 after that.I took the thermostat out and tested it it was bad.Put a new one in problem fixed.But hey you can do whatever you want its your boat.

Good point. I missed that.

The motor is running right around 180 at WOT, which is tickling the temp hi light on the gauge. The other motor doesnt go above 160-170? You can definitely tell that the motor I replaced the impeller is still running too warm by the gauges. So I get this straight, I dont have an oil cooler? I am pretty sure I got all the pieces of the impeller, but is there anywhere else I can look? Would a few small pieces of rubber really cause a drastic rise in temp? I am going to look into replacing the T-stat.

Engine got hot but noticed the light before the alarm even sounded. Motored home single engine, so I am pretty sure I didnt smoke the engine. Only replaced one impeller, but plan on doing the other next chance I get.

i would look into a new thermostat as mentioned...

did you check your raw water intake to make sure you didnt suck up any seaweed, etc

How do I check the raw water intake? I apologize for the idiot questions but I am new to maintaining my own boat. I am pretty handy, but need some direction.

Stopped at West Marine and picked up a thermostat. How do I know which one to get? I picked up a Quicksilver 160 degree but not sure if this is correct for my motor.

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remove the t-stat from the GOOD running motor and mark it 'good'. remove the t-stat from the HOT running motor and mark it 'hot'.

Now swap t-stats from one motor to the other and try that. If the problem shifted to the good running motor, you know you have a bad stat. If the problem exists on the same motor, you know yoiu have a blockage or water flow problem somewhere in that motor.

Sometimes you think you backflushed it enough only there are still some stuck pieces that need alittle more pressure to come loose.

It probably is wrong as in the break down you need two gaskets and the plastic ring.You will more than likely break that ring so just get a new one.It may not be that but when throwingt parts at stuff start with the cheap stuff first.They have probably never been changed anyway.

Also did you put a temp gun on the engine to see what its really running at?

No, I do not have a temp gun. Can you borrow that from an auto parts store?

Just replaced the thermostat. The kit I bought contained the proper gasket. I guess I will have to wait until I take the boat out this weekend to determine a difference. Just to verify that I am doing things properly.

How do you backflush the cooling system to ensure all rubber pieces are retrieved?

Thanks guys for all your help and advice so far.

Replaced the impeller on the stbd motor and decided to swap pumps to see if port water pump is bad. Port motor is still running too warm (around 170 at idle). Took it out in the bay to see if I had any changes when running high RPM. Above 4000 RPM water temp creeps up above 180, hi temp light comes on for a few secs, and then the temp falls off back to 170 or so. This cycle repeats. I have pulled lots of hoses looking for missed impeller pieces. Anything else I can do before I take my boat in for service? Thought about switching temp sensors between the 2 motors.

How did you make out with this?