Help- new remanufactured 350 over heating

Just repowered this spring. Mechanic out of town for a week so I thought I'd seek an opinion

Did first shake down run this week end. Trying to break in correctly...running at various RPM's, nothing less than 1500 and nothing more than 3800; although I did hit WOT (4700) for about 5 seconds to make sure prop/engine aligned

After approx. 30 minutes of varying RPM's (most of run was at 3200-3400) the "alarm activated" although the temp gauge was at 175. I immediately shut down, checked oil and drive oil...everything good. Starboard manifold very hot, port manifold hot.

Called for a tow to slip after the almost 3/4 hour to dock, temp was down to 135. Started engine and limped into dock and tied up (no more than about 3 minutes)...no alarm

Came back yesterday AM, started cold engine and ran at about 2200 RPM with no load....obviously temp gauge went up to just below 175.....both manifolds initially were cold and seemed to be getting circulated water.....as engine ran for approx. 15 minutes or so, the port manifold still remained cold, but the starboard started to get very warm...no alarm...it looked like thermostat did kick in as the temp dropped slightly on gauge, built back up and then dropped again...starboard still very warm and getting warmer (Gauge may be suspect..it is 10 years old and I plan on replacing this week)

I did reach mechanic by phone....obviously he wasn't able to fully diagnose...first he thought I picked something up on out drive....no I checked...and.I wasn't in shallow water so I shouldn't have picked up any mud.....then he thought it might be pump (although this is allegedly brand new)

Mechanic indicated to me that he put in new manifolds (and the risers were only 1 year old and good) when he re-powered and new outdrive pump

If it was a pump failure, why would one side seem to be getting water and no the other..it would seem obvious if I "picked up" something on the outdrive, it would have cleared and both sides would be flushing properly

I'm no mechanic and I'm stumped

Any one run into this before or have any ideas...I don't want mechanic chasing ghosts...he wants to pull and look at outdrive pump and put in a lower temp stat...said he might need to put a second cooling system in with a through hull scoop fitting...I've never needed this before,,,the boat is 14 years old and the standard outdrive cooling system has been fine in past.....boat is a Trophy 25" W/A I/O Alpha drive

Thanks

What thermostat are you running?

Should be 140-143 degree....

All I/O's one side runs hotter than the other as much as 30 degrees or so, so not uncommon. If base temp was lower it would not be as bad but they still get hot!

No need for a different water intake if the original is free from defects. It ran fine all those years before I doubt it wont work now if all the parts are functioning correctly.


Gage is not your problem but if the thermostat is cycling enough to cause high swings in temp then maybe it is suspect.

Also if he did not get the impeller replacement right and missed something then exhaust could be getting sucked into the incoming water and that would cause a over temp condition very easily.........water should be mostly clear of any bubbles and if there are a lot then that air does not cool the motor well.

Thanks..I think mechanic believed stat was 160...which was in remanufactured motor...he wanted to changed to 140 when he returned..the manual says it is a 160

I guess pulling boat and checking impeller wont hurt

kghost said:

What thermostat are you running?

Should be 140-143 degree....

All I/O's one side runs hotter than the other as much as 30 degrees or so, so not uncommon. If base temp was lower it would not be as bad but they still get hot!

No need for a different water intake if the original is free from defects. It ran fine all those years before I doubt it wont work now if all the parts are functioning correctly.


Gage is not your problem but if the thermostat is cycling enough to cause high swings in temp then maybe it is suspect.

Also if he did not get the impeller replacement right and missed something then exhaust could be getting sucked into the incoming water and that would cause a over temp condition very easily.........water should be mostly clear of any bubbles and if there are a lot then that air does not cool the motor well.

Click to expand...

If you are running a 160 degree thermostat on a raw water cooled engine then the nominal temp will easily be 170.

Especially on a new motor the temps can be a bit higher as everything breaks in.

So hitting 175 is easy.

Yup service manual says 160 degree thermostat.

So 175 would be acceptable...................

Do you know what the thermostat was in the original motor and or what the running temp was in the original motor?

Thx for info But...why the alarm and the higher heat on starboard..I guess we'll need a heat gun...I assume the alarm sender is different than the gauge sender an I'm not sure when the alarm sender kicks in

I know the original motor had a +/- 140 stat

kghost said:

If you are running a 160 degree thermostat on a raw water cooled engine then the nominal temp will easily be 170.

Especially on a new motor the temps can be a bit higher as everything breaks in.

So hitting 175 is easy.

Yup service manual says 160 degree thermostat.

So 175 would be acceptable...................

Do you know what the thermostat was in the original motor and or what the running temp was in the original motor?

Click to expand...

Dont waist time.. swap thermostat to 140.
Then enjoy your boat.

When the temp gauge moves does it move fast? Is this a Gen2 Alpha drive?

I'm not sure if it is Gen2...1999

I should have mentioned, the gauge slowly reached 170 and held there even at WOT (the gauge drops a little when it looks like stat kicked in when at high idle)....it was the internal alarm that got my attention and that is when I initially checked manifolds....of course gauge could be bad. It had to be heat related because engine oil was full and drive oil was full....when engine cooled alarm silenced

Mechanic finally got back Thurs. He SAYS he changed stat to 140, changed stat housing, put in new pump in outdrive and checked hoses, manifold and risers and can't find any obstruction....but he SAYS he isn't satisfied that water volume at stat is sufficient and the starboard side is running hot/warm (on muffs....we haven't put it back in water)....he says he is "stumped" and wants this week to work on it.....I asked him about possibility of gimble housing water supply obstruction but I haven't heard form him yet

I'm stumped (not to be cute)....I've googled this issue way too much this weekend....bad pumps/bad impellers/bad stats/bad stat housings/improper manifold gaskets (full flow vs restricted)/Mercury service bulletins

I know I shouldn't be having this much trouble with a new re-manufactured engine with less than 2 hours on it

I do appreciate the input...my faith in the mechanic is starting to drop although I have had him for years

At times when impellers fail, they "shed" pieces. If a piece of the impeller gets stuck in the wrong place in your engine you can get strange overheat symptoms. One place they hide is in the T'stat ports, another in the water dump ports into the exhaust stream in the elbow.

The gimbal housing water supply issue is for bravo outdrives when the incoming water is sucked thru the drive.

The way the exterior hose and interior hose is connected it is Pinched into place, no hose clamps and barbed fittings. The pinch area is all aluminum and is oxidizes with that white stuff which grows over time (corrosion?) and squeezes the tubing causing a restriction.

You have an alpha that should not be your issue unless the water hose at the gimbal is pinched or collapsed...

When you say warn/hot on the riser (elbow) there is nothing wrong with that as long as engine temp does not exceed 160 when fully warmed up.
The reality is the temp is actually around 155 but gage typically show 160.

The elbows will get fairly hot to the touch. Hands should be able to make contact for maybe about 30 seconds before OUCH!

But that is normal in my opinion. Initially they will be cool to the touch but in about ten minutes or so they will get warn to hot.

One will be as I said 10 -30 degrees hotter that the other........just the nature of the design.

So next test get a infa red heat gun and get some temp measurements.

That way there is some data to go by and just a description.

One other question

there at least two different thermostat housing designs.
One only has two outlets going to the bottom of the exhaust manifolds, The other has four outlets and two of which go to the elbows and the other two go to the manifolds (bottom) also.

Which do you have?

The first design with only two outlets will cause the elbows to run much warmer due to the fact the water passes thru the exhaust manifold first and the water is already warm/hot before it reaches the elbows as compared to the system with four outlets. At least I believe this to be so.....
Please respond with an answer to this question
Thanks

Jack...4 port stat housing....I am told it doesn't have "balls".......I have to call mechanic this AM.....he indicated he would get out heat gun, but I'm not sure what manifold temps he is getting....right now he is using muffs unless he dump it in water, he has to trailer it over to ramp a mile away

Thanks for info on gimble housing....that seemed to be the only place he didn't check if he is telling truth... hope he checked manifolds and risers, but this shouldn't affect water volume at stat housing, correct??

Frustrating doing this log distance...I may have to take a day off this week and stand behind him (I HATE DOING THIS)....boat is at our home a Jersey shore, but I stay in suburban Phila during week

sandkicker said:

At times when impellers fail, they "shed" pieces. If a piece of the impeller gets stuck in the wrong place in your engine you can get strange overheat symptoms. One place they hide is in the T'stat ports, another in the water dump ports into the exhaust stream in the elbow.

Click to expand...

Thanks......I don't think the impeller failed, but he did change pump anyway.....I'll make sure he checks the exhaust stream elbow, he said he replaced the stat housing with my old one as a check, so I know he has been working in that area of the cooling system

pdw911 said:

Jack...4 port stat housing....I am told it doesn't have "balls".......I have to call mechanic this AM.....he indicated he would get out heat gun, but I'm not sure what manifold temps he is getting....right now he is using muffs unless he dump it in water, he has to trailer it over to ramp a mile away

Thanks for info on gimble housing....that seemed to be the only place he didn't check if he is telling truth... hope he checked manifolds and risers, but this shouldn't affect water volume at stat housing, correct??

Frustrating doing this log distance...I may have to take a day off this week and stand behind him (I HATE DOING THIS)....boat is at our home a Jersey shore, but I stay in suburban Phila during week

Click to expand...

Wrong reply


4 ports does not answer my question.

If only TWO OUTLETS then you have a 4 port housing. Two in and two out so to speak, One of the "in" is the recirculating coming from the engine water pump.

If FOUR OUTLETS then you have a 6 port design. If the 6 port, 4 outlet is the one being used then the BALLS should be installed, They are poppet valves that regulate water flow to the elbows

kghost said:

Wrong reply


4 ports does not answer my question.

If only TWO OUTLETS then you have a 4 port housing. Two in and two out so to speak, One of the "in" is the recirculating coming from the engine water pump.

If FOUR OUTLETS then you have a 6 port design. If the 6 port, 4 outlet is the one being used then the BALLS should be installed, They are poppet valves that regulate water flow to the elbows

Click to expand...

Sorry......If I recall only a two outlet 4 port housing....(looks like 860256A4 Mercury Part)... was told by Mechanic I didn't have poppet's (when called him broken down...I was hoping I could quick fix myself) so that would make it so

Ok

Then I would say that the elbows will be warmer then a 4 outlet design with the poppet balls. The cold water coming out of the two outlet ports travel up thru the manifolds before reaching the elbows thus taking with it a lot of extra heat to the elbows once the engine has warmed up completely.

So the elbows will run hotter. How much? I have never actually measured it but I have felt it many times.

I consider this normal.

If anyone disagrees please chime in.

So in the end, if your motor maintains 160 degrees or slightly less at idle and slightly more at high speed under load then I would say you are good to go.

The temp sensor that sends the over temp alarm may be faulty as it is a "snap switch" and when it snaps closed it does so based on a preset temp setting (most likely a bimetal spring of some sort).

Maybe it is too low for your application based on the 160 thermostat if it is set to snap shut around 170 degrees???

Was this the same temp sensor as used in old motor?

If the old motor had this same temp sensor and a 140 degree thermostat in it then the answer is clear. You were running too high a thermostat based on the old original sensor based on the thermostat used in the original motor.

kghost said:

Ok

Then I would say that the elbows will be warmer then a 4 outlet design with the poppet balls. The cold water coming out of the two outlet ports travel up thru the manifolds before reaching the elbows thus taking with it a lot of extra heat to the elbows once the engine has warmed up completely.

So the elbows will run hotter. How much? I have never actually measured it but I have felt it many times.

I consider this normal.

If anyone disagrees please chime in.

So in the end, if your motor maintains 160 degrees or slightly less at idle and slightly more at high speed under load then I would say you are good to go.

The temp sensor that sends the over temp alarm may be faulty as it is a "snap switch" and when it snaps closed it does so based on a preset temp setting (most likely a bimetal spring of some sort).

Maybe it is too low for your application based on the 160 thermostat if it is set to snap shut around 170 degrees???

Was this the same temp sensor as used in old motor?

If the old motor had this same temp sensor and a 140 degree thermostat in it then the answer is clear. You were running too high a thermostat based on the old original sensor based on the thermostat used in the original motor.

Click to expand...

thanks...good question.....I had a 140 degree stat on the original motor....Maybe I assumed it was a new sensor with a new motor...I'll have to ask

what you indicate makes sense....we may be chasing the ghost of a bad snap switch coupled with the original 160 degree stat

I went to the Mecruiser web site for the specs of the engine...I couldn't find a rating for the temp switch, but some were I saw one that I thought was 200 deg F..maybe 'm wrong..I couldn't find a part....I did find plenty of temp senders for he gauge, however

I am not saying the temp switch is bad...it could be but if it is design to alarm around 180 or so and you run a 160 thermostat you could have been on the edge.

If original motor had 140 stat and the same temp switch the i would guess after installing a 140 stat you should be ok...

I will see what i can find on the temp switch snap temp...

kghost said:

I am not saying the temp switch is bad...it could be but if it is design to alarm around 180 or so and you run a 160 thermostat you could have been on the edge.

If original motor had 140 stat and the same temp switch the i would guess after installing a 140 stat you should be ok...

I will see what i can find on the temp switch snap temp...

Click to expand...

Thanks.....mechanic just called and informed me he is taking boat out at high tide tomorrow with heat gun.....new 140 T-stat and he replaced the pump with OEM Mercruiser instead of the new Sierra he installed this spring and replaced the riser gaskets (I wonder why??)..he says he checked everything else thoroughly and can't find any obstructions or pinched hoses

I asked him to check snap switch.... I have a new temp gauge and sender I'll put in this week end.....gauges are all 10 years old so I got a new set I replaced oil gauge already because it was bad

Fingers crossed...if it heats up again I'm in for a long argument (I'm sure) with Mercruiser

Once again, thank you for the input... appreciate it greatly

Could not find a spec anywhere...

Best I found was the same as you. A reference to 200 degrees..........

But I cannot confirm that is the spec for all or any.

Up date...and thanks to those that replied

mechanic ran boat and used IR temp gun ...stat housing running about 110 degrees +/-...warms up...stat kicks in and temp drops back to the 100-110 range and then continues to cycle

Starboard manifold is running (when hot) about +/- 125......port is running about 10-15 degrees less.....I called Mercruiser tech support...they confirmed that starboard will run a little hotter on his engine with raw water cooling

He replaced stat to 140 and changed pump from Sierra that he put in to a Mercury OEM (he indicated the Mercury pump had sturdier gasket assembly)....he also changed riser gaskets...he indicated that temp sender and temp snap switch were both new and came with engine

Temp gauge didn't go over 150....I'm changing it (all) anyway to match the new oil gauge

I have a "gun"...I will repeat his tests tomorrow....I'll run the boat "hard" (within break in specs) and keep fingers crossed At least my tow plan up to date