Signs of a bad head gasket - '89 Mariner 200

[tristanlee85]

Originally I was trying to troubleshoot a terrible hole shot after a new jack plate (see https://www.screamandfly.com/showthread.php?344021), but now I have a feeling there is more to not able to get up on plane than just my set back.

Last weekend, while trying to get up on plane with a steady 4k rpms, the motor completely shut down and would not crank over. I thought a ground connection was crap because I replaced the starter over the winter and figured I didn't get the main power cables tights. After messing around with that and knowing the connection was good, I tried again and it cranked over. Thought it was simply electrical.

Later that day, same thing happened while up on plane. After taking the hood off, there was a good bit of water in the cowling. I had a leak on one of the lower water lines and the seal around the regulator/rectifier was leaking. Fixed those and tried again.

Today, just as soon as I got out of the idle zone to take off, it struggled to get the rpms up and then just immediately died. No stuttering. Just completely shut down and wouldn't crank. I trimmed all the way up thinking it had to have been getting water in the cylinders and trimming would possibly help pour it back out through the intake. Well, something poured out anyway. I could see a mix of oil and some fluid (water or gas, assuming water) dripping from the intake. So I am thinking head gasket at this point. I had to bump the starter a number of times to finally get (what I assume) the flooded cylinder to finally clear and crank over.

It idles fine and has no problem revving up, but as soon as it gets under heady load it is done.

I checked compression (cold) after I brought it back and all cylinders were reading 120 - 125psi. Looking through the plug hole, all pistons look to be the same - oil on the plugs and on the top of the piston. None of the piston tops look washed out.

I was hoping to have crap compression in a cylinder to lead me toward an obvious bad head gasket, but I suppose there are other ways to have a blown gasket with compression.

I also feel like it runs hotter than it should. I don't trust my AutoMeter gauge to be terribly accurate, but the temperature will climb to 210 - 225* if I am cruising. The temp alarm has went off in the past and I babied it back (when the water pump was bad). The excessive heat also leads me to a head gasket that only may be leaking under heavy load.

All temp sensors and water pump are new (OEM), lines and cavities for the cooling system were flushed over the winter with no blockages at all.

Any reason why I shouldn't start replacing the head gaskets? I am not sure what else could be causing this.

[Merc 2.5]

Usually a comp guage will point u at a gasket but sounds like it's ok, 210 225 is way way to hot I thought the alarm was supposed go off round 180 190ish. What bout ur poppet ??

[flabum1017]

it's possible it's seizing from overheating. My 140 Johnson did the same thing a few times til I found the cause of the overheating. Take a good look at your cylinder wall for scuffing/aluminum transfer. Other possibility is something in the ignition system is getting too hot and shutting down. Need to address the overheating mainly, but also look for secondary damage due to the overheating.

[tristanlee85]

Usually a comp guage will point u at a gasket but sounds like it's ok, 210 225 is way way to hot I thought the alarm was supposed go off round 180 190ish. What bout ur poppet ??

That is why I don't trust the gauge reading. It may not be properly calibrated to work with the resistance range of the OEM temp sensor.

Here is the reading at idle with constant cold water from the hose using my nose cone adapter:



After I removed both the gauge and alarm temp sensor, using a Harbor Freight special infarad thermometer, I measured the 2 heads at the same spot:



Starboard is a bit higher than port side.

Here is a video of readings above each cylinder:
https://youtu.be/mzYcZwwfAug

And lastly, which is very surprising to me, is the result of unplugging each plug wire one at a time and listening to the difference. Notice the top 2 cylinders on both heads have very little change when the plugs are removed. Only the bottom 2 have significant idle change when unplugged. Maybe that is how the ignition system works... I don't know. I know on a typical 4-stroke engine in your car, idle will change immediately if any 1 of the plugs are disconnected. 2-strokes may be different. This is all new to me. Could be the other 4 kick in at above idle. I'm just spit-balling ideas at this point.
https://youtu.be/NZdZflgVJTM

[rock]

If it were mine at this point I would dial indicate and mark each cylinder on the flywheel. Then check each cylinder with a timing light. This will tell you if there is a spark or not and if it's occurring at the proper time. This will also expose possible cross firing issues.
You did amaze me by not getting knocked on your ass pulling those plug wires. I even look at them too close and I get nailed.

Rock

[Merc 2.5]

I'm with rock. Noway I'd grab those by hand and prob standing n water , u prob got sum switch box issues. sounds ok on hose but then again 2 or 3 of the plug wires didnt make any difference to the idle, grab a timin lite and see if it will lite up on all the wires. Pull plugs and see if u got sum really black ones

[tristanlee85]

I pulled all the coils and tested the primary and secondary resistance and they were all the same - not identical values but consistent. I swapped the plugs around and still the same with the bottom 2 making the most impact at idle. In fact, I pulled the wires from the top 4 plugs so it was only idling on the bottom 2 and while I could tell a difference in sound, it was still idling better on the bottom 2 cylinders than all cylinders minus one of the bottoms.

I used a timing light and it was flashing for all wires.


At idle, the starboard wires were all timing at 4* to the right of the 0. On the port side, I was only able to pick up the .462 all the way to the left of the 0. All wires on each head were consistent with each other.

I did notice this crack, which looks like it leads to one of the boxes on the starboard side. I couldn't find a diagram online as to what they 2 solenoids (?) do. Edit: these are for the trim

The other solenoid below what is pictured here isn't cracked. Not sure what this could indicate.

This is difficult to diagnose because none of this testing is happening under load where the problem occurs.

[tristanlee85]

Could this be a stator issue causing weak spark/no spark under load? I had replaced the voltage regulator/rectifier either last year or the year before using a new CDI unit.

[flabum1017]

That solenoid is for the trim/tilt..... blue wires are up, green are down.... the starter solenoid will have yellow/red wires. The cracked one may have gotten hit by the cover while being put on.

You will need either a spark gap tool or a KV meter to check for how strong the spark is

I like using the KV Meter because you can check the spark with it running.

[flabum1017]

As for the four being weak on power, I'd be doing a sync and link on the carbs..... the bottom carb might be cracked a little at idle making the other 4 cylinders seem like they are not firing as well.

[Motv18]

When you swapped the plugs did you see a different look on them after swaping.

I would start honestly whit number 1 and 2 pulling the wire and idle not changing means it wasn’t working.

[Motv18]

When you swapped the plugs did you see a different look on them after swaping.

I would start honestly whit number 1 and 2 pulling the wire and idle not changing means it wasn’t working.

[FMP]

How much are head gaskets , how many places could it be sucking or seeping water? Process of elimination.

[flabum1017]

How much are head gaskets , how many places could it be sucking or seeping water? Process of elimination.

I would think he would have clean plugs if he were pulling in water

[89Talon18]

7 pounds of water pressure at idle on the hose? Whats your water pressure when your running wide open