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Rapidly fluctuating temperature and overheating after impeller failure - Issue and solution in my 2015 22VLX

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Just posting this here in case someone searches while trying to solve this issue. 

I had an overheating issue earlier this year and figured it was my impeller as it had been in for 3-4 years.  Now... I know they are supposed to be changed every year, but in the 22VLX it is a very painful job due to the transom step being dead center over the pump.   The job is basically totally blind and done by feel.  Its such a terrible design that I almost feel like it was on purpose to be sure you bring it in to the dealer... I digress.  I am fairly mechanically inclined and restore land cruisers for fun.

Well, there is basically no way to get leverage to pull the impeller out if it is at all stuck,  Ultimately after a bunch of different tools, I broke down and bought an impeller puller from Bakes to get it out (again not fun to do blind).  The impeller was shredded and none of the fragments were in the impeller housing.  So on to the disassembly of the cooling system to get the parts out.  

Here is the water flow for a 22VLX

From the water intake on the hull water flows first to to strainer basket on the starboard side of the transmission.  Hose then goes from strainer down starboard side of engine and then wraps around and up to the impeller pump which is mounted on the stern side of the engine (front of the block).    The outlet side of the pump sends water all the way back forward to the port side of the transmission.  The water then exits the starboard side of the transmission and travels down the starboard side of the engine (again) where it enters the starboard heat exchanger which is mounted obliquely on the block aimed towards the thermostat housing.  THIS IS WHERE THE FRAGMENTS GET CAUGHT.  To get the fragments out, take the hose off the inlet side of the heat exchanger.  This is done by taking the hose off as it enters the inferior and lateral part of this heat exchanger and sweeping your finger up inside the exchanger.  There is a strainer in there that traps the fragments.  Dump the water line that you disconnected down to get any additional free floating parts out.  Next, I took the thermostat housing off.  This is done by removing 6 allen bolts on the intake manifold and lifting it out of the way.  The Thermostat is a 160degree indmar monsoon 350 t-stat.  I changed it and found only a few small bits of impeller in here.  Need 2 separate gaskets to do this job.  I replaced the t-stat while I was in there.  


The impeller was replaced next.  When you pull the plate off the back with a slotted screwdriver, keep track of its orientation as it is not symmetric and the gasket is difficult to line up if you cant see it!  I prepared the new impeller by putting 3 zip ties on it so the fins bent for clockwise rotation when you are facing the engine on the swim platform for installation.  I let it sit like this for 24h so they had a bit of memory.  When ready top replace it, I cut the zip ties off as I pushed it in.  Dish soap is mandatory to get it in when doing it blind.  Actually went in fairly easy with the soap and zip ties.  I tapped it in one last time with a small rubber mallet.  I then put quite a bit of dish soap in the housing as it was going to be dry until suction was generated.  To replace the cover, I put one screw through the plate and then the gasket and finger threaded it back on.  To get the second screw, I gently rotated the plate and gasket to ger them lined up while finger threading the second screw.  

Once I fired the boat up, I saw suds coming out in the exhaust confirming water flow through the system.  

After running the boat for a few days, I had another intermittent overheating issue.  Wildly fluctuating temperature.   I was worried I did something wrong, but based on the fluctuations, I felt that there may be a flap of debris still in the system.  Base on my first experience, I took the heat exchanger hose off first and voila there were 3 additional impeller fragments, one quite large.  After I cleared it out again I have had zero problems.  

So the lesson here is that the fragments float around until they find there way downstream - even 5-10 engine hours later.

I'll be replacing the impeller for frequently now.

Hope this helps.

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Thanks for the info it could help a lot of people with the same issue.

I hear you on the blind impeller issue.  My Malibu model has it on top and it's easy to access but I previously had a Chaparral with Mercruiser 6.2L and the impeller is on the bottom of that engine.  I had to buy a remote/wireless camera system and angle it down there because I couldn't see where the bolts were to get the impeller plate off.  First time I changed the impeller it took me 2 hours.

Boat engineers who design the engine layouts should be required to work with the service techs who actually do the maintenance on these engines so that they can see how their choices make maintenance way harder than it needs to be.


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