Mercury V6 Overheating: Clogs? Impeller? Poppet Valve? Thermostats?

Mercury having issues with overheating. Symptoms: Alarm was a solid beep which means overheating. There could be a number of reasons for overheating. Clogs within the cooling system, bad impeller, faulty poppet valve, or bad thermostats.... Today I dig into why this V6 is overheating. As always, Thank you for watching! Any questions or comments please leaving them below!!!!
Link for T-Stats used in this video:
amzn.to/3OFvrxE
poppet valve kit:
amzn.to/3UdNV9q
impeller used:
amzn.to/3EJr1kD

[@DJHale68]

The thermostats are there only to increase the block temp at idle and just off-idle . Once the speed comes up and the increased pressure opens the poppet valve the thermostats close and have no effect on engine temp. I believe you have a flow blockage elsewhere in the block and/or covers. All the water flow from the pump comes up thru the center of the block and makes a right angle bend into the exhaust cover just below that big plug at the top of the block. Pull that plug and look down the hole to see if there's debrii blocking the flow just below there into the exh cover. good luck!

[@GeeWizGod]

Thanks for all the great videos you put out on these motors. I just got a 1985 1175 and it’s dead at the moment. But with all the videos you have hopefully I can bring it back from the dead and get her talking again.

[@joway97]

I look forward to your post regarding Mercury outboard trouble shooting and repairs. I don’t have any boat motor repair experience. I have got my boat on the water because of your post. I appreciate your sharing.👍🏾

[@MerCSonL6]

It's coming my friend. Son

[@gautevaland879]

Great vid Son! Looking forward to the follow up on this owerheating issue! 👍😎

[@ct1762]

right so im sure you know this, but just to explain why you mentioned poppet valves for others: poppet or "pressure relief" valves are for high speed cooling only however if they leak/arent sealing/grommets bad, its like a straw with too big of a hole ie. the water pump cannot pump water high enough in the block because the poppet valves are reducing pressure.

[@j.z.h.fishing5678]

so it’s the water pump that’s not letting The water go all the way to the powerhead . which causes the powerhead to be hot to the touch?

[@MrCantrucker]

All your stuff is great. Didnt know it had 2 therms. lol learn something new everyday

[@brookesmilbourn3188]

All the older V6 mercs can throw you off The Tell-Tale is plumbed in differently than a lot of other Outboards since they are plumbed to the output side of the thermostat you will not get any water out of the stream until they completely open or sometimes they will spit and sputter lots of times being mistaken for a bad water pump, not to sad the pump isn't bad but alot of people don't understand how this system works. For that fact I always check for water pressure at the gage and I use a tank rather than muffs

[@mercoutboardsinlines6s371]

great video!!!!

[@qfastqfast]

Do you have any videos on changing out a poppet on a black max 2 stroke? I’m having issues with over heating at full throttle. I’ve replaced all the lines and thermostats, impeller kit. Still the same. I don’t think the water jackets are caked up but I might have to take it apart next.

[@greauxpete]

Another test is to measure the temps at the center of the thermostat housings with you IR thermometer. The temps on both should be near your t-stat opening temps.

[@Nathanmr19771]

I have the older model 78 150. I replaced impeller thermostats and poppit valve. I’m assuming the newer ones water route maybe different but mine comes out the upper exhaust ports first before the tattle tale and my tattle barely dribbles at idle and flows good at speed. I’ve watched cylinder head temps with no over heating. I’ve given up on getting that perfect stream at idle unless I’ve missed something 🤷‍♂️

[@MerCSonL6]

If its not broken don't fix my friend lol. Boats are already high maintenance. Thank you for your comments. Son

[@vandos11]

that's a good thermostat trick

[@MerCSonL6]

Thank you my friend. Son

[@matt18333]

For troubleshooting have you tried it in a bucket? I can't see much water coming out of the prop exit either so looks to not be getting the pressure it needs somewhere. Water pump housing looked alright? Maybe drop the gear box and back flush through the tell tale hoses for any contamination.

[@MerCSonL6]

Great idea 💡. That's in my next video which I have already done but not produced/released. Thank you! Son

[@WorkHardPlayHarder]

Another helpful video! Do you have a vid on changing/replacing reeds? My 89 mecr 115 broke down and can't find anyone around me that will work on an outboard older then 90. One guy did look at it & said: " it won't start cuz its not sucking in air, which means the reeds are bad" He said its pretty much an ⚓ now and I should just toss it. I had just spent $1k getting new cdi, carbs rebuilt & bleeder valves replaced in Jan. (By a mechanic that said the motor was strong & that it was worth putting $ into it! Unfortunately, that guy retired and moved to FL. So am I just screwed or is replacing the reeds something I can do????

[@MerCSonL6]

I've has engines with bad reeds and they start just fine. Hard to get the idle low but they run. Are you 100% sure it's the reeds?

[@WorkHardPlayHarder]

@@MerCSonL6 No, I'm not sure! That's just what the only mechanic in my area said he thought it was, although he spent more time trying to get my to buy a motor from him than he did looking at it. Quick background (try anyway): I was given the pontoon for free & the boat/motor had been setting in water for 4 yrs. I cleaned out gas lines, pulled and cleaned starter & sprayed seafoam in plug holes an added new plugs. It fired right up! But the dirt dobbers had completely covered motor with mud so I cleaned it and had carburetors cleaned & rebuilt. I took to lake and started right up, drove for maybe 20mins and the throttle got stuck so I had to literally jerk it into neutral to stop from hitting a dock! Motor cut out about 30 seconds after that and has not started since. Tried cutting the kill switch wire to see if it was that & changed out inline fuse on motor. It sucks gas in cuz I drained carbs & then tired starting and they filled again. Checked spark, was good and even changed plugs out just in case. I can feel it pull skin on my hand while its trying to start but the mechanic had sprayed some power stuff around it and said if it was getting air like it should it would have sucked that cloud in, which it didn't. So thats were Im at now.... Someone on boat forum suggested it might be something with control box and said to try a different one, which I don't have. I have been looking for an 8 pin harness to try to make a universal switch like in your other vid but haven't come across one yet. Do you sell those by any chance? Anyway, I would appreciate any help!!! You can email if thats easier: [e-mail] Thanks!

[@ct1762]

@@WorkHardPlayHarder i havent seen reeds as a cause of poor running in 20 years I think ive had to replace 2 sets of reeds at the shop. its not the reeds lol. thats what a terrible mechanic says when they dont want to work on it... or dont know how. even if there is .005'' of clearance, the reeds will seal fine. if its not starting, check compression and spark. if those are fine and it still wont idle or start, take the cylinder heads off. most likely piston skirts are shot.

[@ivita7316]

Hi Jonathan here. I just watched your video, as i am having i beleive a similar issue. Mine is a 30hp 4 stroke. I removed the thermostat (has 1 only) to see if that would do the trick, no luck, so i removed the thermostat housing and ran to see if i had good flow, which i did. I am getting sometimes steam out my pee hole but sometimes not? But my engine is getting way to hot. I was thinking a blown head gasket ( which by looking at all that smoke you had maybe thats the issue?) Or clogged water ways around the cylinders, but not sure? Or both? I dont believe my engine has a poppet valve, but if yours does, i would definitely look at that one. Did you ever figure it out? Thanks for the video... Look forward to your fix info.

[@MerCSonL6]

Yea.

[@biodot88]

I like a dummy basically ran an entire oyster bar through my water pump. I changed the pump and still overheats/steams. I will change out the thermostats. But can you flush out the galleries to make sure they are clear?

[@MerCSonL6]

I don't see why not my friend. Son

[@johnp3427]

Not sure if you remember me, but you came over to my house and picked up a motor for your friend. I never did see if you got it running. I'm over in Berkeley Springs.

[@MerCSonL6]

What engine was it my friend? The 40hp?

[@johnp3427]

@@MerCSonL6 yes. It's the one you said you wanted to fix and give to your friend.

[@MerCSonL6]

@@johnp3427 I did give it my friend Mike Kise used it to rebuild a rare xs model! Thank you so much my friend!

[@johnp3427]

@@MerCSonL6 my pleasure

[@Hitech82]

Great video. I had the exact same problem. Put the new thermostats in.. 152°trolling 152° running at 4k rpm The Bay water is 84° The motor feels a little cooler than the water. What do you think? Is thus a good operating temp for my motor?

[@MerCSonL6]

Perfect 👌

[@Hitech82]

@MerCSonL6 thank you so much. My boat has 450hrs on it. Runs great..can't afford a new one..thank you

[@daveyt4802]

How about junk from the hard lake water? Flush for those systems?

[@diejeffy]

How would you compare the performance of the V6 to the I6?

[@MerCSonL6]

More problems with V6s vs L6s. L6s are built to last.... V6s not so much. But if you want more power V6s are the way to go. Just be prepared to spend more money. Just my 2 cents. Son

[@earlsulfridge435]

Any tips on changing water pump on 90hp

[@MerCSonL6]

Just be sure to align 3 things upon reinstall: crank, shift shaft, and water tube. Son

[@floridareelnoutdoors1992]

I’m having a problem with my black max mercury 175 I just replaced the water pump an at idle it pumps water great an at full throttle it stops pumping water an when I stop it starts pumping again

[@MerCSonL6]

That's definitely a weird issue to have. I would rebuild the water pump again. Something is not adding up. High pressure and it stops pumping? Definitely a unique problem to have. If you rebuild the pump and have the same issues then you know it's something within the powerhead. Son

[@SuperSnook40]

If you have a good stream out the pee hole then pump is working, Check your Popper Valve, coukd be clogged with its spring stuck, if it's all corroded up falling apart then replace it & I bet your issue is solved.

[@hooked_fish]

This smoke 💨 is normal?

[@davidjessee7701]

I would have tested the old thermostats!! You can’t look at a thermostat and say it’s bad just because it’s corroded

[@MerCSonL6]

I couldn't even push the springs down..... they were rock solid my friend.

[@JroyBulldoggin]

Why would my xr6 not be pissing, it’s not clogged, I just replaced the water pump.

[@MerCSonL6]

Blockage in the block? Does it piss when you hook a hose directly to it?

[@byronwatson9038]

Change the water pump base plate. They get hot and lose their shape.

[@albertcomisari9447]

poppet valve

[@mrBDeye]

You’ll destroy the motor running it out in the open like that. Even with water-muffs you should only run the engine for a short time.

[@davetyson2331]

teltale water comes after thermostats open that is water is hot

[@MerCSonL6]

Correct. Son

[@giicllc8819]

Hi Jonathan here. I just watched your video, as i am having i beleive a similar issue. Mine is a 30hp 4 stroke. I removed the thermostat (has 1 only) to see if that would do the trick, no luck, so i removed the thermostat housing and ran to see if i had good flow, which i did. I am getting sometimes steam out my pee hole but sometimes not? But my engine is getting way to hot. I was thinking a blown head gasket ( which by looking at all that smoke you had maybe thats the issue?) Or clogged water ways around the cylinders, but not sure? Or both? I dont believe my engine has a poppet valve, but if yours does, i would definitely look at that one. Did you ever figure it out? Thanks for the video... Look forward to your fix info.

[@MerCSonL6]

Clogged water ways....