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Old 06-09-2017, 07:43 PM
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TyTanium TyTanium is offline
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My LY6 idle overheat solved

I have a direct drive, open cooling system LY6 and was having the common overheat at idle. It happened every time I used the boat....it was manageable by increasing the idle, but it happened every time.

I installed clear hoses on the engine and spent about a week trying different thermostats, different sized bypass holes, no thermostat, relocated thermostat, etc. etc. From what I saw, I believe the overheat at idle is a result of low water flow thru the engine at idle. I know that sounds painfully obvious but I think most of the water from the raw water pump goes out the exhaust while the engine is at idle. Increasing the RPM to around 1,200 doubled the water drawn out of the engine by the engine water pump. That explains why a small increase in idle RPM brings the temp back down.

With this information, I focused on increasing the water flow thru the engine at idle. I tried drilling several combinations of bypass holes in the thermostat. I initially tried an 1/8" and a 3/16" bypass which definitely got the temp down. Ok, problem solved....not so fast. With this combo, the temp would intermittently become erratic. It would swing 20 degrees either direction, then would settle back to 160. The difference though is it would come back to 160 on its own (not by me increasing the RPM like before). What I think was now happening is the additional cool raw water was interfering with the thermostat causing it to close, then some hot water would hit it and open it again. What I did to alleviate that problem was to add another thermostat to the output of the engine water pump and increase to (2) 3/16" bypass holes. This way, the top thermostat is controlling the water temp, it only sees the water leaving the engine (not the cool raw water) and increasing the bypass hole size in the bottom thermostat provided enough water flow that it didn't matter if the bottom thermostat was closed.

I ran it this way for a few hours and it was solid. It ran 160 and every now and then would drop back to 150-155 then right back to 160. After I was confident (and wanting more temp), I put a 180 thermostat up top, and a 190 thermostat in the factory location (the 190 basically being a fail safe for the top one). I've put about 10 hours on this configuration and it runs 180 and every now and then drops to 170-175 then back to 180.


Parts: $120
Inline thermostat housing: Meziere WN0071
Top thermostat: Stant 453858 (drill (1) 1/8" bypass hole)
Top water pump hose: Napa 16122 (cut one end to fit)
Bottom thermostat: Murray 52387 (drill (2) 3/16" bypass holes)

Top hose with inline thermostat installed:
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1/8" bypass hole drilled in top thermostat:
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(2) 3/16" bypass holes drilled in bottom thermostat:
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Trimmed gasket around bypass hole (don't forget to do the other side!):
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Install bottom thermostat with bypass holes at the 4:00 and 8:00 ish position:
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Feel free to take this info and further experiment. This combo is much better than before in my engine. I don't look at the water temp as often as I use to.....which is nice!

Last edited by TyTanium; 07-06-2017 at 05:52 PM.
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Old 06-10-2017, 09:35 AM
JagNL JagNL is offline
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Awesome thread and great work, thanks for posting this! Do you think the factory water pump gets weak over time? What gets me is my LY6 seemed fine/never overheated at idle all last season and then had issues this summer. Strange we'd have to go such measures to prevent idle overheat.
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Old 06-10-2017, 09:37 AM
JagNL JagNL is offline
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Also, why 180 degrees? I thought factory was to run at steady 160 like your first config? Any advantage to letting it run hotter?
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Old 06-10-2017, 09:38 AM
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Old 06-10-2017, 10:22 AM
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For those that bought the LY6 new/newish. Was this a common problem right from the get go, or did this develop over time as the boat aged?
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Old 06-10-2017, 07:31 PM
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TyTanium TyTanium is offline
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Quote:
Originally Posted by JagNL View Post
Awesome thread and great work, thanks for posting this! Do you think the factory water pump gets weak over time? What gets me is my LY6 seemed fine/never overheated at idle all last season and then had issues this summer. Strange we'd have to go such measures to prevent idle overheat.
It wouldn't surprise me if the factory pumps get weak over time. I replaced my engine water pump a few weeks (pardon the pun) before doing the testing so I can't comment on the flow of a used pump.

If anyone knows a way to put a smaller diameter pulley on the water pump, that may be the ticket!
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Old 06-10-2017, 07:40 PM
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TyTanium TyTanium is offline
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Quote:
Originally Posted by JagNL View Post
Also, why 180 degrees? I thought factory was to run at steady 160 like your first config? Any advantage to letting it run hotter?
The data I read says engines run more efficiently in the 180-190 range. GM designed this engine (clearance wise) to run in the 195 range. Additionally, one of Indmar reps told me the engine would like the higher temp.....he said the Coast Guard requires them to keep the engine at 160 to prevent burn injuries otherwise they'd operate it hotter. I might regret it, but for the above reasons I'm gonna try the hotter temp and see what happens.

Last edited by TyTanium; 06-11-2017 at 12:28 PM.
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Old 06-11-2017, 12:31 PM
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TyTanium TyTanium is offline
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Quote:
Originally Posted by osmonet View Post
For those that bought the LY6 new/newish. Was this a common problem right from the get go, or did this develop over time as the boat aged?

I've wondered the same thing. Hopefully someone will answer.
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Old 06-11-2017, 03:20 PM
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osmonet osmonet is offline
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Quote:
Originally Posted by TyTanium View Post
I've wondered the same thing. Hopefully someone will answer.


Seems like a slightly smaller diameter pulley on the recirculating water pump would do the trick???
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Old 06-11-2017, 06:57 PM
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TyTanium TyTanium is offline
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Quote:
Originally Posted by osmonet View Post
Seems like a slightly smaller diameter pulley on the recirculating water pump would do the trick???
Yeah, that would spin the water pump faster. The more I think about it though, only doing a smaller water pump pulley probably wouldn't overdrive it enough to make a difference.....might need a bigger crank pulley as well....which might require a larger alternator pulley. That's probably not as good of an idea as I though it was, lol.
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