2.5l mercury overheating

**rgsauger** · 07-07-2022, 10:41 AM

Originally Posted by Smalltownbassin

Less than a year.

Sierra or better or cheap chinky stuff?

**Smalltownbassin** · 07-07-2022, 04:23 PM

Originally Posted by rgsauger

Sierra or better or cheap chinky stuff?

Genuine PRUFREX boxes made in Germany from sierra international. Its funny because the first set they sent were clearly chineese knockoffs. I called and explained what i recieved and they apologized for supply chain issues and sent me the genuine boxes. The genuine units are what failed. I also bought a genuine CDI trigger , stator & reg at the same time. I had a set of used genuine CDI boxes that i just tried too but same issue. May just be the trigger but likely both. Or like Robert said, may be the light weight flywheel doing the damage to begin with. I checked the magnets the best i could. No cracks and even poles all around on the stator magnets. The hub magnets are the ones that im not real confident in checking and if its the magnets causing chaos id assume its probably the hub magnets for the trigger pulse. Ive still got some more verification to try before i burn up another ignition but im definitely on track now. No doubt at all about double fire. Just need to find the gremlin causing the failures now.

**Smalltownbassin** · 09-15-2022, 04:35 PM

What a freaking ride! Sad thing is.....im still not sure its fixed. Picking up where i left off, new set of SBs toasted immediately, then another set, and another, and another. Somewhere between one of those another's' i installed a new trigger & stator. Same double fire. All 6 coils are sparking on time but also showing other holes. Called CDI. Spoke to a knowledgeable tech who suggested a specific type of coil test. Turns out i had a bad coil on #4 & #2. Put a new set of coils and ignition wires on. Seemed fine on muffs but overheated on the water. Got it home and found the new coil wire on #2 was OL. I figured since #2 was likely not firing, #4 was reaching overheat temp before the stat opened. Got that squared away and its doubling down again! One more set of SBs, flywheel, stator & voltage regulator later, its firing normally! Woohoo! But the SOB still got up to almost 170 on muffs pretty quick. Wind up taking a carbide burr to the LWP holes and almost doubling their diameter while also dropping separate stat dump hoses out the heads instead of the usual bridge with a single dump. Down to 150 now on muffs. Gonna water test this weekend. Just in case...anyone wanna buy a boat? LOL jk

**pcrussell50** · 09-15-2022, 06:33 PM

Small… After watching your youtube videos (and commenting

) I watched another one last night and in that case the guy pulled the powerhead and literally traced every path the water could take, looking for blockages. In the end, he pulled hard plastic bushing, press-fit into the block, that the poppet valve goes in and out of. He found quite a bit of corrosion under that bushing, which was causing the poppet to stick. After he pulled that bushing and cleaned off the corrosion, it sat right again and didn’t stick. He is hoping that solves his overheat problem.

Disclaimer, it was a Mercury but not a v6. Still, the idea of following the whole water path seems reasonable, especially since making flow improvements seems to have helped your situation.

-Peter

**Smalltownbassin** · 09-15-2022, 07:26 PM

Thanks Peter! And yeah thats not a bad idea. Already done that more than once lol! But.....in everything ive looked at, i always had those pickups in the back of my mind. Seems like half the area as a stock case. Not sure if opening them really did anything since i changed the dump hoses at the same time but dang sure didnt hurt. Now with each head having its own dedicated 3/8in dump line, its moving quite a bit more water when the stats open on muffs and cools down a bit like it should. Poppet opens fine too. A quick goose on the throttle shows it opening by a sharp pressure drop followed by a slower rise with rpm. Dumps a ton out the exhaust at the same time also as it should. IDK man. I feel like ive been chasing the actual problem around and finding other things as i go while the original problem was still causing trouble. Ill definitely find out saturday. Its not double firing anymore which it was doing for certain. Maybe it was a combination of these things.

**OnPad** · 09-15-2022, 09:49 PM

Wonder if your bad coils would have shown up in a bias test on switchboxes? If they were bleeding off into ground system?

When you doubled up your thermostat dumps, how did you deal with the hose that goes to adapter plate?
Tee off of one hose? Tee off of both hoses to a central tee to adapter? I've been thinking of doing that mod, so I could catch a stuck thermostat, before meltdown.

**LakeFever** · 09-16-2022, 07:46 AM

Are you still running those scorched pistons or did you rebuild again? Id still fatten up the fueling to the point of fouling plugs. Lean burns hot. Still all said and done at this point swapping a factory non coned lower on there to test would make sense. This doesnt sound like much fun my hat goes off to you for staying with it

**Smalltownbassin** · 09-16-2022, 12:02 PM

Originally Posted by OnPad

Wonder if your bad coils would have shown up in a bias test on switchboxes? If they were bleeding off into ground system?

When you doubled up your thermostat dumps, how did you deal with the hose that goes to adapter plate?
Tee off of one hose? Tee off of both hoses to a central tee to adapter? I've been thinking of doing that mod, so I could catch a stuck thermostat, before meltdown.

I T'd off the port side only for now. It is nice to see both stats operating independently of each other from separate hoses too.

**Smalltownbassin** · 09-16-2022, 12:09 PM

Originally Posted by LakeFever

Are you still running those scorched pistons or did you rebuild again? Id still fatten up the fueling to the point of fouling plugs. Lean burns hot. Still all said and done at this point swapping a factory non coned lower on there to test would make sense. This doesnt sound like much fun my hat goes off to you for staying with it

I just rebuilt the one that melted #4 last weekend. Only #4 got a new slug. The rest got new rings. Its on the stand now. This block is the James Perry block i bolted up when the other let go. Been chasing the same squirrel ever since. Ive already tried another standard lower with same results. New pump in that lower also. Im definitely needing some prayers and encouragement lol!

**LakeFever** · 09-16-2022, 12:18 PM

Indeed your up against it here. Id start trying some things to see if anything flags. 1. Increase the octane maybe a few gallons of VPfuel. Id also try and fatten up the fuel, and maybe try colder plugs. Pressure washer through the cooling system.

hmm you know come to think of it i recall one of the more experienced members here having similar problems with a rebuild after a seizure. He said the solve was new sleeves due to the block contact being compromised by the seizure distorting the cylinder. The honing cleans up the bore but does not address the contact problem which messes up heat transfer. Something like that iirc. Grasping at straws here for ya

**Smalltownbassin** · 10-03-2022, 04:15 PM

EUREKA! No more overheating at all. Idles on muffs around 135-145 and warm to the touch after a run. In a million years i would have never thought that a coil that's firing on time could also be bad and causing switchbox failures due to back feed. <<<Good to know for sure.

I really do appreciate all the input and help. Now i can work on getting it tuned and when i blow this one up the Frankenbeast will be repaired and waiting to claim its spot lol.

**pcrussell50** · 10-03-2022, 09:51 PM

Congratulations. But damn. I hope I never have to chase down a problem as confounding as that.

Which coil was it and how out of six coils, did you track down the bad one?

===

Just when I think I understand this stuff and have it all down, motors all running well, blokes like you come along with a real head scratcher that puts me right back in place. :-/

-Peter

**Smalltownbassin** · 10-04-2022, 05:42 AM

It was actually a CDI tech on the phone that had me ohm the coils while connected which checked good between posts and ground to output which checked good. Then he asked me to disconnect ground and check again. Found #4 to be bad reading in the M range and #2 was intermittently reading high and determined it to bad also. After the new full set of coils and SBs to go with them the root issue is gone.

**LakeFever** · 10-04-2022, 06:07 AM

Hmmm i had an arctic cat that had a strange overheating issue many years ago. About the only thing I never changed was the coil because it ran hard and fast so I never thought it could be a bad coil. Good for you for discovering that and thanks for updating the issue. Congrats man, way to stick it out!