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Weird Problem Merc 1997 165 Marinised Chev Str 6

N

northwind

New member
"20’ 1972 Bertram has 165 Mercruiser i/o, which I have about a year ago replaced with a recon straight 6 chev block. since then I have replaced; (correct)coil, condenser, fuel line, fuel filter, points, new fuel pump diaphragm, cleaned out heat exchanger and had the carby done up.I still have a weird problem that I can’t seem to conquer-HELP!!!
Predictably after 20mins of running at normal revs when it reaches approx 85 degrees, (100 for us is boiling) the engine falters for 30 secs and then cuts out. It wont immediately restart but after 30 secs turns over, after 5 mins it will restart and take revs but wont take any load in gear without choking.
It slowly regains and might run for 30 secs then a minute, then a bit longer, until after it cools down, it will run fine again for the same 20 mins and then back to square one.
Do you know if there is an (oil?) overheating switch fitted to the Mercruiser engine that could cause this problem?
I have had 2 mechanics and an auto electrician look at it to no avail.
I was thinking fuel, then electrics, then fuel and now I am at my wits end – !
Possibly it could be a broken ignition wire that stretches with heat(unlikely) or even fuel vaporising in line. I’m fairly sure its not a blockage in fuel tank or lines because its so heat related. Its not fuel tank pressurising - checked.
Any help is much appreciated before I rename it from ‘Northwind’ to ‘The Bitch’
Everyone suggests ripping the guts out and putting a pod & outboard which I am loathe to do. I'm sure its going to be a $5 problem but I cant find it.
What am I missing here?"
 
Also I have put new spark plug

Also I have put new spark plugs and all new leads.Changed metal fuel line (from pump to carby) from over top of motor to rubber slung under motor (cooler position)
 
What is 160-180 farenhiet in y

What is 160-180 farenhiet in your measurment.

Because anything over that is overheating.

So for this post i will assume you are not overheating.


When it shuts down do you pull a spark plug wire and insert a spare plug into the wire and hold it to the block and crank the motor to see if you are missing spark?
 
1.8 x 85 + 32 =185 deg`s F

1.8 x 85 + 32 =185 deg`s F so it`s running warm but not really overheating.
 
"Ok so lets say you do in fact

"Ok so lets say you do in fact have spark because you verified the moment the cut out occurs.

Then it is fuel related, so here is what i would do.

I would remove the fitting that enters the carb and clean the screen that should be there.

I would make sure the screen inside the fuel pump is clean, if there is one there.

I would remove the hose the enters the fuel pump, and plug the hose that runs to the pump.

I would run a hose from the fuel inlet to a external tank of fresh gas.

I would then run the motor, and it should not cut out see you have good spark, correct, because you verified that already, and you have good clean gas running to the carb.

It runs good doesn't cutout, then it's gas tank related; what follows is a post i made to a different website copied and pasted here.

I pumped all the fuel out of my onboard fuel tank when i got it.

You can do one of 2 things, pump the water out of the bottom, or all the fuel out and here is how.

If you just wish to pump just the water out of the bottom of the fuel, you will need to purchase a cheap electric fuel pump from any auto store dc powered.
You will also need about 15 foot of cheap fuel hose from the auto store and clamps to fit the fuel pump.

Install the hose on the fuel pump both ends and cut about five feet on the sucking side of the pump just look for the arrow on the pump.

Remove the fuel pickup tube it's the one where the fuel hose hooks to the tank a 90 degree angel fitting, it's a anti-siphon valve. Unscrew it.

Crank the bow of the boat all the way up, and stick the hose connected to the electric fuel pump 5 feet into the bottom and back of the tank.

Into a clear container pump the water out till you see clean fresh fuel and stop the pump.

Or into a large container pump all the fuel out.

Now check the valve by blowing thru it, check the screen thats its clear.

Install the valve and pickup tube your done.

Question do you have a fuel water separator on the boat, good to have.

Ok now lets say you do have the problem it cuts out.

Another rebuild of the carb done by someone who knows what they are doing.

Run the boat. Should now have good spark, good gas. Should run good.

If it still cuts out then i would redo the valves.

When i say redo set it up with proper lash adjustment, run the boat.

Now i am going to have to believe, that the boat is tuned up, timed correctly. Before anything is done to it.

Please keep us informed after you try all the above, good day's work.

I didn't post all my little tricks so do inform us of the outcome."
 
All above sounds helpful but i

All above sounds helpful but it sounds heat related. I think the engine is too warm. When was the impeller last changed? Change the T'stat to 165 F. or 74 C.

Was the distributor rebuilt or serviced? Some of the wiring may be old and corroded. When it heats from current flow it can open the circuit. Check the battery connections for corrosion and meter them for voltage drop. Don't just look at them; remove them and inspect them. Old wiring will be corroded internally and brittle. It can be cracked and heat affects continuity.
 
"plenty of boats run 185. But

"plenty of boats run 185. But it could be the heat exchanger needs cleaning, could be the flapper / shutter fell down is partly blocking the exhaust.

Could be the riser is half clogged, or could be the t-stat is half frozen closed " i run without a t'stat "

Could be that the main ground needs cleaning, the connections on the block. Who knows first lets see what i posted before works to see if he has spark when the cutout occurs, then take the fuel out of the equation.

See if no spark and he posts that, then i say run a jumper wire straight to the coil, will take out the main harness out of the equation and any other wire that might be internally corroded. The main harness plug also could be the problem.

Could also be a corroded connection in the main fuses. Could be the slav. Could be the ignition key. He have a kill switch.

He posted the problem is ongoing from the moment he installed the new motor.
The valves being to tight could be the very cause, my friend received a fresh motor, the valves were to tight, way tight drive us crazy had the same symptoms. Maybe he should try reseting the lash on the valves first and run the boat. The to tight valves could cause the motor to run hot also.

But in the end we don't know for sure till we find out, if it's spark or fuel thats causing the problem.

Guy your good very very good. Don't want you to think i'm jumping on you or anything, you have my deepest respect."
 
"Use a P of E (process of

"Use a P of E (process of elimination)
One item, and one item ONLY as you go through a list as you diagnose for the problem.


FYI, fuel related issues generally do not require 20 minutes to raise their ugly heads.
Me thinks ignition.... possibly a coil issue. But again, this is just simply too difficult to diagnose via a forum.

While throwing a few ignition parts at it may not be a bad thing...., generally speaking, if we throw enough parts at a problem, we will eventually solve it..... <font color=""ff0000"">and I am NOT suggesting this!</font>

What I am suggesting, is to use the P of E.
If you do this, it will better prepare you for future similar issues.

You've been given a few things to check..... that's what I'd do!
."
 
chiefalen:

Thanks for the v

chiefalen:

Thanks for the vote of confidence; your methods and ideas are fine w/me. My head told me to check for a defective wire and impeller. I'm weak on engine inernals.
 
"Everything i posted wont cost

"Everything i posted wont cost a dime, if the boat is already timed and tuned.

I once replaced a coil that wasn't the problem, not bad for 45 years maybe more turning wrench's."
 
"Ah but it can! If it takes 20

"Ah but it can! If it takes 20 minutes for your engine to warm and open the choke fully if it's even operating right. It kind of sounds like a lean running condition, even the running a bit warmer than it should. Also check your timing. But that's just where I would start. I'm sure there is long list of eliminating processes."
 
"I think the int/exh manifold

"I think the int/exh manifold is warming up with the rest of the engine, letting a crack expand releasing water into the engine and killing the spark. Checking the color of the plugs and just pulling them and turning the engine over watching the plug holes spew moisture. I had a new manifold on my 165 not even 8 hours and it cracked. 185f isn't warm for that engine but air temp and air circulation does have an effect.
An Old Riser will cause the engine to run hot, can also let water back into the engine.

Was a marine cam used in the rebuild? or is it a truck/car cam.. (there is a slight difference)

It could also be water in the fuel. I would touch or use a Laser Temp tool on the Coil to see what it's doing.."
 
"Gentlemen - I am overwhelmed

"Gentlemen - I am overwhelmed with you help and advice - Firstly a big "THANK YOU!".
Secondly I will take all of this info to an old salty boat mechanic out on one of the Islands near here.
Also in answer to a couple of things that I can reply to without sounding too ignorant. Yes I did check the tank vent. I am worried you may be correct about the water entering the engine and killing the spark. The reason I had to replace the old block was exactly that. The people that replaced the block claim to be Mercruiser 'specialists', but what happened the first time I took it for a run after the new block was put in it ran fine up the river but immediately it stopped it over heated - the mechanic claimed he had the tolerances too fine. They rebored it. Next run (this will amuse you all) I just got out of the bay 5 mins and the engine shut down, I opened the engine cover to see a bilge full of oil. I didnt even look at it I just took it back - they claimed a drip of paint prevented the oil filter from seating properly. Strangely I haven't been back to those cowboys once they fixed up their mess. I am unsure if a truck or marine cam was used in the rebuild.
Anyhow timing is all just checked and OK.
I will take it out again to get it to this point check for spark and check it with a plastic fuel tank. This boat has always seemed to have an overheating prob. It takes in salt water and runs it around a heat exchanger which I dont think copes very well. Also the cowboys took out the thermostat and shut off two of the circulating water vents that are on the pully end of the motor claiming they weren't necessary. I was going to join them with a piece of hose again to improve water flow.
This thing has a diesel motor type fuel filter with a glass bowl underneath, which is new, the flame arrestor filter on top of the carb is clean.
The impeller is less than a year old but I will check and replace that - and yes the distributor is the ancient original brown bakerlite which I have wondered about. I did put new points and condenser in but wondered if on heating and expansion a wire was separating there. Maybe Sherlock Holmes is available!
Batteries are less than a year old but wiring on the motor is original so maybe I will take out an auto electrician for a spin with his tools.
As I said earlier I have replaced the coil and it had no effect on problem. The problem first started showing up when I went flat out trying to keep up with a friend in a faster boat and immediately on lowering revs it faltered and stopped making an interesting arrival in port. It seems to have gotten worse and showing up sooner and at a lower temp ever since. Thanks again guys."
 
"THis " and immediately on

"THis " and immediately on lowering revs it faltered and stopped " and this "shut off two of the circulating water vents that are on the pully end of the motor " .. concerns me.

lowering revs then faltering says water injestion... I'd have to see the vents that are plugged.. you can see pics of my engine here.. I know of 1 vent but can't think of the other...

I'd need a pic. I know the inline 6 pretty good.. but I ain't no Inline Racing Mechanic.

http://gallery.kainonmedia.com"
 
"Thanks Brian, I will snap a p

"Thanks Brian, I will snap a pic and post it - I'm about to head home, my engine is similar but has fresh water thro the engine. Is the water ingestion
a matter of replacing head?"
 
"This is the view of the close

"This is the view of the closed water ports at each of my thumb & finger the ports aim left and right
374760.jpg
waterports
 
"There is also a red reset but

"There is also a red reset button to the left of the radiator cap - could this be the thermo problem?
374763.jpg
Red Reset Button
 
"You can see the small heat ex

"You can see the small heat exchanger here too - Any further help & comments are much appreciated and welcome. Again Thanks
374769.jpg
spagetti coils
 
"Anthony: i wish you would hav

"Anthony: i wish you would have included all the info of the last post sir in the original post.

I have been studying your pictures,i lost count how many straight 6's i had my hands on. Was actually the first motor i rebuilt. I was 16 at the time, i posted about it on another website maybe if i can find the post latter i will copy and paste it here.

Ok if it were my boat i would yank off the heat exchanger,and all related hardware, and set it aside, and place a t'stat housing on the manifold where it usually sits. No t'stat in the housing.

Side note any 4 cylinder 2.5l or 3.0l or straight 6 t'stat housing will fit they are all the same. Doesn't matter if it's a omc or merc housing.

It's actually easy, run a hose straight to the t'stat housing from the transom, in effect turning it back into a raw water cooled motor.

The hose you need are already installed on the motor.

Run it to see if the overheating problem has been resolved.

Not resolved off comes the riser. Check the riser to see if it is all plugged up. While off i would see if the flapper / shutter fell down and plugged the exhaust.

Now lets assume the riser is good or you replaced it. And the flapper / shutter is good or you removed it, i would re-install the riser.

I would run the boat again.

Ok riser replaced or good , you run it and it still overheats, then it's time to remove the manifold.

Manifold has to be pressure tested.

May i ask a question? How does the oil look thru all this overheating? Is it overfull, water in the oil?

The more i read about your woes with this boat and motor the more i feel for you.

Want to enjoy your outings on the water, and all you get is grief. Let's see if we can get you sorted out, see i have no financial gain trying to help you, and the other, better, mechanical minds on this forum have the same goal.

All i can do is post what i would do if i were in your shoes, concerning this motor.

Good luck ! Keep us posted."
 
"First Pic, Pinky - in a car/t

"First Pic, Pinky - in a car/truck that's where the water would normally go to a heater. The thumb port is where water exits the thermostat housing and goes to the Riser and exits the boat.

The Red Button is MAIN POWER Breaker/Fuse.. It could be your problem and is easily "Temporarily" Bypassed.

The Thermo Thingy below the Flame Arrestor Warms up with warm air going up through the tube in the Intake/Exhaust Manifold to Open the Choke.

Since you have SEA Water Going through the Intake Exhaust Manifold and Riser I would Suspect they are letting water into the engine, I wouldn't suspect the head at this time..
As you dont have Water in the Oil.. Though to much water injestion from the INT/EXH mani & Riser will put water into the oil too.."
 
"As to your "broken down o

"As to your "broken down out in the islands picture"...It really doesn't seem like a problem...it is 17 degrees here and, as I look into my backyard and see my snow covered boat, I can't help thinking that being stuck on a warm island would sure beat this...Good luck with your motor and "come on spring"!"
 
"I once owned a Bert 25 w twin

"I once owned a Bert 25 w twin 165s... When I first got it, the engine started ok when cold (in warm weather) then got hinky as it warmed up. I fooled with it a bit and got nowhere. Then I went to the boat one cool morning and removed the flame arrestor. I looked down the carb bore and found... choke totally open, i.e, vertical. I cycled the throttle (engine off) ... no change. I put my finger on the choke plate thinking it was jammed.... it wasn't. I could close it, but as soon as I let my finger off, it snapped back open.
I checked the other engine... choke closed.

I took off the black plastic cover from the choke bimetal spring housing and discovered.... spring in backwards... No choke when engine cold... 100% choke when it heated up.

I found the receipt in the paperwork that the old owner gave me... a month before he sold the boat, he paid a real marine mechanic to "rebuild" the carbs... :)"
 
"heated and unheated can be se

"heated and unheated can be setup to go in either direction, remove the spring and turn it around. (maybe not applicable in this instance though)"
 
"Ha - I feel for you guys unde

"Ha - I feel for you guys under all that snow, while we are burning our feet on HOT sand. Just doesn't seem like Christmas here tho!
OK., first I will go with the easy option and check the choke spring. - If the heat sender from the i/e manifold was out of whack could it also be a candidate for throwing out the choke setting?
Red Main Power button doesn't seem to help even when by-passed.(If it's working at all...)
Chiefalen - the oil is just normal black I would assume if it had water -it would be a coffee colour? Would that show up on the dip stick or would I need to take out the sump plug to check?
As I am strict about flushing out (+ using coating treatments) after salt water use could I just get rid of the whole fresh water exchanger and run outside water through the motor? I will follow your advice(s) as above and let you guys know the hopefully positive results - This has all been a REAL help to get some hands-on advice, as I was at my wits end with knowing where else to turn with this motor. Once again 'THANK YOU!' By the by, I have the original mechanical servicing books for the 20' Bertram which cover absolutely EVERY aspect - would be happy to scan any info people might need."
 
"Red main button is a breaker,

"Red main button is a breaker, It is supose to open when over current is sensed. It is a normally closed breaker as it is now and is working correctly.

If you have a delayed stalling condition as you say after 20 minutes then I would look at these,
Some or all may have been mentioned allready.

1. fuel issue, either vent clogged causing a vacuum condition on the fuel tank keeping fuel pump from sucking fuel.
Fuel line pick up going into tank getting clogged up and it happens around the same amount of time when under power.
fuel pump is failing and needs a fuel pressure guage installed inbetween fuel line and carb and monitored when running.

Ignition, Is coil getting HOT to the touch in this short period of time?
Look closely at the points, are they clean or very pitted from used or over current,

One other issue that maybe woth looking at and is a problem with inline six and inline 4 cylinders. The distributor is mounted on an angle because of this the dist shaft bushings wear out and allow the dist shaft to wobble inside the housing, If this occures then your point dwell will change and the warming up of the motor will make this condition worse. When the motor is cold the housing and bushings shrink a small amount and the shaft will sipn truer until warm.

To check this, remove the dist cap and rotor and get the points on the top of one of the high points of the dist cams, push and pull (not twist) the dist shaft and watch the points, if they open and close a lot with this movement the the distributor MUST be replaced.

Also when it stalls you must remove the flame arrestor and see if you have fuel squirting down the throat of the carb when activating the throttle linkage and as said before that the choke is fully open. This will eliminate a fuel issue.

You must also check for spark as soon as it stalls, Remove the coil wire from the dist cap stick a spark plug into the wire end and hold it near a good ground ( engine block or screw head) and have someone crank the engine and if the point ignition is fuctioning then there will be a spark jumping the spark plug gap, this will eliminate the ignition from bieng functional or not, It does not say it is working corresctly though!!

Well that is enough for now, let us know what you find out......"
 
"[b]If the heat sender from th

"If the heat sender from the i/e manifold was out of whack could it also be a candidate for throwing out the choke setting?

The Heat sender is a open tube, that when the manifold warms up, it warms up the air inside it, there by warming up the Choke Coil. If the Choke is not set Properly or is Not Working Properly or the Choke Coil is Wrong/Backwards then there will be problems.

to Test the choke coil let the engine sit over night, take the flame arrestor off, without starting the engine, and with out touching the controls see if the choke plate is OPEN or Closed. Then Move the Throttle ONLY lever to MID Position then Back. The choke should close (almost) completely If it closes completely or not at all it needs to be adjusted. There should be a small 2mm-3mm Gap between the choke plate and the side of the throat of the Carb. To tight and it will be too rich startin or be hard starting.

If it doesn't close try to move the plate and see why, could be sticky linkages could be the choke coil is not adjusted enough or is the wrong one or is broken.

Red Main Power button doesn't seem to help even when by-passed.(If it's working at all...)

If you put a 12v Meter to both sides(terminals) on the Red Power Button, you should have 12v, when the engine shuts down, have that be one more thing to check. Mine is 1974 vintage and still working. In Fact I've had a couple instances where it Shut off Power and I had to push it to start up and run again."
 
"re: "If you put a 12v Met

"re: "If you put a 12v Meter to both sides(terminals) on the Red Power"

To clarify.... Black meter lead to ground, use red lead to check both sides of button."
 
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