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hydrolocked engine

H

HollywoodXJ

NAXJA Forum User
Location
Manhattan, KS
a couple of weeks ago i hydro locked my 4.0l in my cherokee. i pulled all the spark plugs out shot quite a bit of water out of my #6 cylinder. drove back to town chained oil and my TPS sensor went out and i replaced it. now i have a very fast tick it seems to be worse when i start the engine after it has been heated up. is there anyway to fix the tick? a friend suggested to tighten the rockers but i dont know how to do that any help would be great.
 
what kind of rpm's were you running when you locked it?

When I did mine I changed the oil twice within a week to be sure. Try some Marvel mystery oil in the oil to see if you have a stuck lifter. I doubt that your rocker ams will have anything to do with it, to check you would pull the valve cover and give them all a feel for tightness. You could be hearing a bearing, lifter, or possibly just some valvetrain noise that you had gotten used to and now stands out since you are looking for problems.

btw: the clock has started ticking. I give you 4000mi give or take 500mi till you toss the number 6 rod out of the side of the block. I have known 5 people who have locked one, including me, and all failed within 3000 to 5000 miles of the hydro incident. Mine ran great for 4k. It was a reman with only 50k miles on it. So I would start keeping an eye out for either a block crank and rods to make a stroker, or a complete block to swap in, cause the odds are against you keeping that one for long. water is the one sure weakness of a 4.0.

good luck.
 
wolfpackjeeper said:
...,water is the one sure weakness of a 4.0.
Click to expand...
Water is one sure weakness of ANY piston engine. Any sudden stoppage event is bad for an engine, hydro-locking it is probably the worst.

As wolfpackjeeper said, start planning for a short block soon.
 
HollywoodXJ said:
a couple of weeks ago i hydro locked my 4.0l in my cherokee. i pulled all the spark plugs out shot quite a bit of water out of my #6 cylinder. drove back to town chained oil and my TPS sensor went out and i replaced it. now i have a very fast tick it seems to be worse when i start the engine after it has been heated up. is there anyway to fix the tick? a friend suggested to tighten the rockers but i dont know how to do that any help would be great.
Click to expand...

Start shopping for an engine NOW. It's not a matter of If you ruined the motor, It's a matter of when it grenades. There are plenty folks on here that thought there motors were OK, weeks later they post up a WTB 4.0 thread.
 
he would have to change all the rods, it is not the bearing, but the stress cracks on the rods that are going to cause one to let go. The shock force of hydro'ing the motor produces cracks in the castings of the rod and they fail later, RPM not dependant.

My #6 rod let go at about 1400 RPM cruising at about 45mph. BAM! gone. Then it sounded like a couple of squirrels playing with ball bearings and firecrackers in my block.
 
wolfpackjeeper said:
he would have to change all the rods, it is not the bearing, but the stress cracks on the rods that are going to cause one to let go. The shock force of hydro'ing the motor produces cracks in the castings of the rod and they fail later, RPM not dependant.

My #6 rod let go at about 1400 RPM cruising at about 45mph. BAM! gone. Then it sounded like a couple of squirrels playing with ball bearings and firecrackers in my block.
Click to expand...

It doesn't stress fracture the crank as well?
 
not sure, I have never reused one. But it is almost always a rod that lets go. I would not reuse the crank, might as well get a 258 crank and rods right?
 
Yeah, that engine's time is limited. Did the same thing on mine. Hydrolocked it, started to tick. Thought it was a lifter. Replaced them and the sound stayed. Only happens when hot too. Several thousand miles later the #5 piston decided to move to the oil pan.
 
When you hydro lock your engine, the connecting rods are very susceptable to bending.... It may be only a slight bend but it is very serious none the less..... the tapping noise you hear is because the rod length is now shorter and the piston skirt hits the crank shaft counter weights at bottom dead center..... Once a rod is bent it will do several things like make the piston ride crooked in the bore, which is another potential knock, put a side load or crooked load on the respective crank journal and cause premature bearing failure, and a bent rod is no longer strong..... compare it to having a long thin piece of steel rod.... If you exert pressure to the ends of the steel the thin rod will be strong until it gets to the point where it bends, once it bends it will continue to bend very easily..... A bent rod has a great deal less strength than a straight one, this is why they have a limited life and will break..... a hydro locked engine is repairable if you do not continue to run it and further the damage....
 
Except when it is mis diagnosed as a hydraulic lifter failure. I'm sure my failure could have been prevented by replacing that single piston/rod.

Couldn't the only damage to the engine after hydrolocking be the piston though and not the rod? They are fairly brittle pistons, so I see that them failing prior to the rod easy. Either way repair is necessary and being that since you already have the engine open the cost to replace a rod and piston vs a piston only is small.

-Chris
 
Why do you keep talking about a single rod & piston. In a hydrolock situation there are more than one piston and rod moving upwards on the compression stroke.

Remember air/ fuel mixture compresses, water does not. With the momentum of the engine turning, the water isn't gonna give so the rods bend.
 
You are right.. multiple pistons/rods could be damaged. I was thinking about my situation where only one piston/rod had the problem.

Edit: BTW, my engine lived for 7800 miles before it died after hyrdolocking with the sound. When mine let go I was going 70 mph. No noticeable sound... just lack of power and a big black cloud. It was the piston that fell out, the rod was still intact. It actually ran with #5 piston in the pan and the rod and pin dangling around in the cylinder.
 
Last edited:
Talyn said:
You are right.. multiple pistons/rods could be damaged. I was thinking about my situation where only one piston/rod had the problem.

Edit: BTW, my engine lived for 7800 miles before it died after hyrdolocking with the sound.
Click to expand...
Don't get me wrong, I have hydrolocked two motors in my life. One was an army truck, one was a customer's truck. Both were diesel's(witch I feel are over-engineered anyway). Both had the injector's pulled before attempting to re-crank.
 
Talyn said:
Except when it is mis diagnosed as a hydraulic lifter failure. I'm sure my failure could have been prevented by replacing that single piston/rod.

Couldn't the only damage to the engine after hydrolocking be the piston though and not the rod? They are fairly brittle pistons, so I see that them failing prior to the rod easy. Either way repair is necessary and being that since you already have the engine open the cost to replace a rod and piston vs a piston only is small.

-Chris
Click to expand...
Damage to the piston is rare..... It is the rods that bend that is the problem....

If pistons were "brittle" they would never survive the violence of combustion....

It is kinda funny to see this thread..... My 17 year old son just hydro locked my cherokee and actually broke 2 rods..... Yea, I said broke, not bent....
 
boojo35 said:
Damage to the piston is rare..... It is the rods that bend that is the problem....

If pistons were "brittle" they would never survive the violence of combustion....

It is kinda funny to see this thread..... My 17 year old son just hydro locked my cherokee and actually broke 2 rods..... Yea, I said broke, not bent....
Click to expand...

Actually the stock pistons are considered brittle. They are hypereutectic pistons, which aren't as durable as forged. The combustion process is a pretty much controlled process. Its when you get into uncontrolled events like pinging and hydrolocking that they fail. These pistons are far from forgiving. Also they don't lend themselves well to forced aspiration.
 
ia green96 said:
Don't get me wrong, I have hydrolocked two motors in my life. One was an army truck, one was a customer's truck. Both were diesel's(witch I feel are over-engineered anyway). Both had the injector's pulled before attempting to re-crank.
Click to expand...

Did they survive for any length of time after that?
 
Talyn said:
Actually the stock pistons are considered brittle. They are hypereutectic pistons, which aren't as durable as forged. The combustion process is a pretty much controlled process. Its when you get into uncontrolled events like pinging and hydrolocking that they fail. These pistons are far from forgiving. Also they don't lend themselves well to forced aspiration.
Click to expand...
Sure stock cast pistons are not as durable as forged pistons..... sure hypereutectic pistons are more brittle than their all aluminum counterparts due to the added silicone.... You are correct that they don't like turbos, blowers, nitrous, etc..... I have never seen a piston that was broken in a stock engine..... I have seen them with holes melted in them etc, from preignition and lean fuel conditions..... I cant even begin to count how many hydrolocked engines I have worked on and have never seen a failed piston from and engine being hydrolocked..... if you continue to run an engine that has a bent rod from being hydrolocked you may have a piston failure but that failure would be from the bent rod..... I have been an auto tech for almost 30 years and spent many years of it doing mostly trans and heavy engine repair....I've seen the inside of about a gazillion engines...
 
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