what are the causes for a blown powerhead?

[aNNieNsaLTIE]

so many rebuilt or blown powerheads out there. from my understanding this isn't cheap to fix either.

why do they blow and how do you prevent it?

Steven

[fishinfool74]

runnin lean, weak water pump. Someone tell me if I am wrong.

[aNNieNsaLTIE]

how do you run to lean? oil mixture?

[Guyle]

Last winter when a bunch of us blew our motors, it was most commonly blamed on not warming up your motor before taking off.

[MikeD]

how do you run to lean? oil mixture?

yes - oil to gas mixture ratio, or just not enough fuel into the cylinders when running WOT/WFO

also not warming up the motor all the way will cause pistons - they have not expanded as they do when they do once they fully heated up - to rock in the cylinders enough so that they leave metal on the cylinder walls - seizure is imminent

or a water pump not pushing enough water thru due to blockage or broken fins on the impeller will overheat the motor causing the oil to breakdown and provide insufficient lubrication

[Slippy]

old age.

[201Pro]

old age.

Hey now, I resemble that remark!

Ken Hitorri at the Boat Dock once told me that the EFI's were 'bulletproof' ... "IF you don't do anything STUPID" with them. I always warm up my motors plenty and my first run of the day is usually at mid-range RPM's (3-4000) ... I would usually make a short run and fish then make a longer run if necessary. Then again, I'm no "pro" ... just a weekend-warrior!

[Dewayne]

Here are a few tips that will significantly reduce the probability of a blown power head. The are opinions based on my experience, feedback from marine mechanics, and talking to people who have blown engines.

Always allow at least 5 minues when motor has been off for more than ~4 hours for the motors temp to rise and the heat to evenly distribute through the motor before running it about 3000RPMs. This is speacially critical in water temps below 50 degrees or on really cold mornings. This is probably the lead preventable cause of engine failures.

Have you water impeller replaced annually. More critical in the Delta or other waterways where you have dirty water, weeds, and sand bars.

Use quality oil.

Do not run a higher octane fuel then the recommended for the motor. Higher octane burns slower and produces more heat.

Keep the motor/rings from sticking due to carbon buildup by burning good quality fuel and running Sea Foam or other system cleaner through on a regular basis.

[TonyL]

how do you run to lean? oil mixture?

Bad , or restricted fuel injector , will do the job ! This should cause a rough run condition . Need ta pay attention ta how your motor is running, if not well , may not be a good idea ta run it till it's checked out.

[drrakruz]

Faulty thermostats is another one to add to DeWayne's list. I've heard conflicting opinions regarding warming up engines.

Think about this. If you warm the engine up before nailing it, the t-stats are designed to open at a specific temperature. If the motor is, in theory, "warmed up", the t-stats aren't necessarily opened. When they do open, a rush of cold water circulates around the power head, thus engine block heat meets cold, circulating water. This is know as "thermal shock". Theoretically, over time, this expansion/contracton of a cast iron block will warp the cylinders and heads, thus, leading to a blown powerhead. This is what I was told by my Merc mechanic.

[David Rogers]

I think Dewayne hit it on the head, exspecially the warm up part, I see so many guys start up the motor and with out a blink they are putting the hammer down, you need to give that motor a second to warm up and get lubed. I know a few guys that had new Opti Max's blow up, I think one of the problems there was that these motors run so lean due to new mfging regulations that the slightest clog not even a full clog in an enjector and there goes one piston!! I can see if you are sponsored or have a waranty but the thing is you are still down for who knows how long. I use Merc oil, the correct Octain and always let my motor run at least 1 minute before I hit the throttle and even than I slowley pick up speed, if I am fishing a tourney I may go a little faster on the take off but not much, you may save 30-90 seconds but this may cause you to be down 30-90 days!!!

Just my .02

[Joe Bruce]

aluminum pistons warm and expand faster than the block. to much oil also causes a lean condition.

watch your temp, know how warm normal is and be carful untill you get there.

any loose bolt, nut, washer, hose clamp, acorn can get sucked into a cylinder. pull the cowell often and look around

most failures are temp or oil related

[tunaman]

watch your temp, know how warm normal is and be carful untill you get there.

Temp is key, not time... it will take longer for the engine to achieve normal operating temperatures in colder environments than it will in warmer environments. It may only take 30 seconds or a minute to get up to temp during the peak of summer, but it can take several minutes to get properly warmed up at Shasta in January.

Roger

[SHAFT]

I posted this last time this topic came up , it's from a Mercury Master Tech. Well worth posting it again .

The first thing I want to talk about is cold water through a cold motor..
1) A outboard motor does not warm up very fast if at all at an idle in cold water.
2)Thermostats can only help it warm up so fast if you have 40 +/- deg. water running through your power head.
So how do you run a Opti or other outboard under these conditions?
1) Idle at least 3-4 minutes minimum.
2) Take off easy.....Do NOT hammer down from an idle while still cold. Take it easy for a ways. Increase the RPM's gradual.
3) Make sure your thermostats are working properly!
* This one is very important ... (I had this happen to me) I was running a 2004 225 Opti in 40 deg. water, motor was running at 130 deg range it picked up a pebble and stuck it in a thermostat (held it open) I had Smart Craft gauges and always have it on eng. temp in cold weather/water..
When the thermostat got stuck open it cooled the motor down to less than 80 degrees!...It would NOT go above 80 degrees even at WOT!
So what's the problem??
First you have a certain amount of clearance between the piston and cylinder wall.
example... cyl bore on a 200/225 Opti is 3.6265 in. (std.) The piston has approx. dia. of 3.6210... So you have approx. .0055 piston to cylinder wall clearance...
Now when a motor heats up it expands...So when it's up to normal operating temp. the piston and cylinder wall are both a larger diameter.
When you run a cold motor hard or up to WOT real quick what happens is the piston gets hot much faster than a cylinder wall that has cold water against the outside of it....The hot piston expands but the cylinder wall hasn't yet....What happens from there is called a Cold Seize.. The expanded piston don't have the .0055 clearance needed and it will seize or stick to the cylinder wall. If it seizes/sticks running @ 5500 RPM + it just rips the wrist pin/connecting rod right out of the piston...The connecting rod will go out of control and end up out through the side of the block...At this point the power head is destroyed...This is one of biggest failure issue of a Optimax and one that can be avoided by just following the above info.by making sure it warms up and has time to warm up right ........Sherm

[mark poulson]

As a new Opti owner (March 08) I want to say thanks for this thread.
My old 50 horse 4 stroke didn't have any problems, but I'm new to the Opti, and really appreciate all the info and advice.

[barse41]

all i can say is make sure you keep that oil tank full or youl learn the same costly mistake as me

[bustout]

i have a 95 efi merc, 200hp ...knock on wood still running like a champ...when it idles a little rough i add "ring free
' fuel additive ...

i never hammer the throttle and increase my rpms gradually, also when slowing down gradual as well.

i think of it like a car...cars last longer if you dont pedal to the metal from a dead stop

also, i rarely run WOT. back to the car...if it is in the redline most of the time...then probably wont last as long ....greater than 5k rpm is fast moving metal !!!

[bustout]

i have a 95 efi merc, 200hp ...knock on wood still running like a champ...when it idles a little rough i add "ring free
' fuel additive ...

i never hammer the throttle and increase my rpms gradually, also when slowing down gradual as well.

i think of it like a car...cars last longer if you dont pedal to the metal from a dead stop

also, i rarely run WOT. back to the car...if it is in the redline most of the time...then probably wont last as long ....greater than 5k rpm is fast moving metal !!!

[aNNieNsaLTIE]

are these blown motors usually the motors that are 150hp and up? or do all motors apply?

i normally warm up the motor while doing some reting of rods in the morning. i tend to even let the motor warm while parking the truck. I respect the no wake zone and idle all the way out.

i do notice my motor run higher RPMS on the delta but i thinkit is due to the current......

[Pat]

Right now and for the next couple months is "blown powerhead season". This is the time of year with cool dry air that is rich in oxygen. This leans out the motor due to higher ratio of oxygen to fuel. Engine will run super strong till it burns a piston. This may be less true with newer motors that that have O2 sensors giving feedback to the computer, as they will richen the mixture some, but it still can be the death of one. My trusted old mechanic Joe White once told me, when you get up on a fall morning and it's nice and cool and there is no dew on the dock, don't run it hard!

I know the first time I blew one up it was running like a scalded dog till I heard that awful sound.

Pat

[bassindon69]

What make and year is the motor?

Don.

[civicrr]

Shaft,
Good info there. I read that on another forum. From that guys posts on that forum, you can tell he knows his stuff. In fact, there are a couple of Master Mech on that forum & all are helpful.

I will add to keep an eye on your water pressure. Recently running in the Delta, I slowed to make a sharp turn. Got back on the gas & it felt weird accelerating back up to speed. Thought I might have imagined it. Glanced @ the water pressure gauage....& it was @ 12psi. Normally, @ 4k rpm, I am running well over 20psi (no jackplate - Ranger 520 w/ 225 Opti). Somehow, I picked up a plastic bag on the lower unit blocking the water intake. Lucky for me, the Opti has the water intake @ the front of the nosecone too. It wasn't blocked. Must have picked it up during the turn.

[aNNieNsaLTIE]

my boat don? I got a 89 merc. 90hp.

[bassindon69]

It's only on every one of your posts (stupid me)
You don't feel it's just old ? I have a 2000 Evinrude 90 Ficht it has been rebuilt half of the motor and the lower end also. There is NO WAY my motor will last another 11 years like yours


Don.

[Dave Wilson]

Also- stuck rings- hence Yamaha's "ring- free" additive. Failed oil injection pumps, and in tons of the mid- late 90's Envinrudes we had wrist pins going through the walls too- can we say "factory defect". I find it amazing that all of them don't grenade the way we run them on bass boats. Lots of great advice offered on this post!!

[YZKEN250]

Yes it can be costly. I blew my 03 Merc Opti 225 last year in Jan. Didnt let it warm up properly. Was going to run me $9600 to fix it but found out it was still under warranty.

[rexford]

The guys that race these engines take the oil injection
systems and throw them in the trash. Premixing fuel
removes most lubrication failures.

[aNNieNsaLTIE]

not rebuilt once yet. wanna keep it like that to!