Merc 2.5 200 overheating .. help/info please !

[FrankieP_516]

I got a 2004 mercury 200 2.5 efi . Motor is stock . I’m getting a overheating alarm (steady beep) when running over 3000+ rpm over cruising speed . Shut off and turn back on Alarm goes off then run it then comes back on . Wouldn’t pee till I rev it . Thought maybe the motor was too high on the boat so lowered it down . Boat is a 17ft Hydrostream with 10bs jackplate I got the top 3 holes plugged and pad level with intake grates . 30p cleaver prop..

I changed the water pump today with all new gaskets and backing plates, went to change thermostats but there was non so out them in. And also changed poppet valve. Non looked bad . Motor still getting hot . But noticed was peeing better and water was warm .

would a head gasket cause overheating or something else I can look at ?

[LakeFever]

This thread covers everything and then some.

https://www.screamandfly.com/showthr...ry-overheating

[Forkin' Crazy]

IMO 30 pitch is way too much. You need at 25-26 at most. That might be a player in your over heating game.

Might be an obstruction in the water flow also. Pulling the heads and exhaust divider might be needed.

[OnPad]

Not to say you don't have other problems, but I'll second what FC said. Your engine needs to be mounted much higher to run that much pitch. Think propshaft above bottom of boat, which would require a lwp.

[Smalltownbassin]

Is the mid and adapters original to a 2.5L? Just helped a guy sort that out this weekend. He had 2.4L adapters under a 2.5L PH. Doesnt quite work out well. 2.5s need more water than a 2.4 plate can provide. If you arent getting a tell tale at idle, you definitely have a flow issue. Just gotta find out why. Check water pump, check pressure gage, Check pump housing, tube and grommet. Check adapters. Check poppet & stats. Check all hoses connections & fittings. Check spark for irregularities. Check timing. Check fuel. Is the entire block heating up or have you isolated it to a local area? Is it one bank or the other? Is it a single hole? Feel free to holler at me with questions. At this point in my life, if a 2.5 is overheating, ive found any and all issues man could dream up that causes it lol! But that old thread Lake Fever was talking about covers it all.

[Forkin' Crazy]

Those motors like to spin up. Needs to turn 6K IMO. If you still have oil injection, delete it. Also a boost pump might be a good idea. Better to do a VST delete and mount the pump in the fuel tank.

Those are great motors!

[Smalltownbassin]

Almost forgot until i read your original post again. Yes a head gasket can cause overheat same as the base gasket and divider gasket. The reason is that exhaust gas can blow out the gasket and pressurize the block water cavity. This prevents water from going where its needed because exhaust gas is much higher pressure than the WP can overcome. This can happen on all 3 gaskets mentioned. And just because the spark plugs don't have water or cream on them doesn't mean your head gaskets are good. Just because exhaust is getting out doesn't mean water is getting in. Best way to tell is pull the heads and check for cream or oily residue in the water jacket around the cylinders or on the gasket where it possibly blew out. This is a sign that the gasket has blown out or isnt sealing well. Replace and/or torque heads again and check. The base gasket is known for burning up and allowing water and exhaust to mix in the adapter or block cavity. Only way to check that is pulling the PH.

[OnPad]

I attempted to run a 35p 4 blade cleaver at 2+ inchs above pad, on a light boat, with a 2.5. I didn't make it 1/4 mile before I had the temp gauge pegged.

[Smalltownbassin]

Those motors like to spin up. Needs to turn 6K IMO. If you still have oil injection, delete it. Also a boost pump might be a good idea. Better to do a VST delete and mount the pump in the fuel tank.

Those are great motors!

Never heard you mention if its got oil injection still other than "stock". Are you getting oil? Good call Forkin'!

[FrankieP_516]

It’s got the oil deleted . It’s the general block heating up . I did a water pump ,poppet valve , thermostats , dual side pissers and actually lowered motor down about an inch cause I don’t have a lwp and went out yesterday seemed to not overheat . I didn’t really step into it but at around 60 it didn’t set off the alarm . I’ll look for a 26-28p prop also . I also compression tested the motor to see maybe I had a down cylinder all 6 right around 130psi . WP around 6 at idle .

[Baker343]

No expert here but a couple things caught my attention.
1. found no thermostats
2. dual pissers

Are you running a 1-piece exhaust plate and if so the poppet is useless, unless it's a PM 1-piece plate or it's been modified to work with a poppet.

Is this Hydrostream and engine new to you.
Never stated what WP you had at around 60mph
Should have no problem spinning a 28-30P as long as you have 15-20psi at your max rmp's.

You may have to pull the power head to make sure your exhaust plate is right. Modified or not because people will try some weird things chasing Cold seizing, Hot temps, low and high WP.

Post some pictures of your power head water dumps and exhaust plate or plates