At wits end with overheating problem!

[DannyChaos]

The car:1991 240sx
The motor:Ka24de-twin cam
The problem:F'ed if I know but it ends up overheating.

Car has 130,000 on it and compression check shows 160ish across all four cyl.
About a year ago a new water pump and stat were installed due to the car running a bit hot.
Cooling problem was solved and the car was parked for about 6 months after that ,being started about every other week and run till stat opened than shut down.Car is now back on the road and has had a few new parts put in it.Parts are:clutch kit, tps,fuel filter,plugs/wires,oil change and cleaned maf.After the parts were installed I took her for a spin and all seemed on the up and up.Drove the car for a good 150miles through a 2 day span with no problems at all,stock temp gauge sitting at 1/4 and not going any higher.Now here is where shat gets tricky.I drove the car over the weekend for about 5 hours straight with no issues and than when I was pulling into a parking lot it decided to jump fast into the red about to overheat.I shut it down and popped the hood to find the coolant bubbling into the overflow,grabbed the upper hose it was red hot and hard,lower hose was piss warm and soft and while the temp gauge was climbing the heat coming through the vents was getting cooler and cooler. I let it sit until the heat dropped and the overflow dropped back down,popped the cap off and it was still full.I figured I had a bum stat and went n grabbed a new one and some coolant.I blew all the hoses out through the motor ,rad etc,every thing seemed to flow nice with no clumps or chunks of crap.Tossed the new stat in and filled her up,with the front end nice and jacked up burping out what I believed to be all the air in the system.I took the car for a test run and the problem seemed to go away.3 days of no cooling problems and than at random after a nice long drive it jumps way up again! I do the same thing again,figured I may have got a junk stat and swapped it out for another,flushed out the system again burped it again etc etc...Long and the short of it is this,the car will randomly overheat at no specific point of driving every now and than and I can not for the life of me find another case like this.You can leave the car idle for hours and it never gets above 1/4 the way up on the temp gauge "yes I understand that the stock gauge is crap and should not be trusted" You can drive the car hard,soft for 10 min or ten hours and it never has any issue.But the lower hose never seems to get hot ,just piss warm,the upper hose gets red hot and full,the heat works till the temp gauge goes up,Im not leaking or burning anything,I burped and bled the air out and still at random it overheats.I am at the point that I can not keep pulling all nighters trying to figure out what the hell is going on.If you guys have any ideas please feel free to throw um this way.Sorry for the long write up ,just wanted to make sure I gave a full run down so we are all on the same page.Thanks in advance
Dan

[sx moneypit]

You have all the symptoms of a head gasket that is seeping.

[DannyChaos]

What would be my best way of testing for seeping? Other than the compression test that I already did?
Would there be any other symptoms if it was in fact the head gasket seeping?
Thank you

[Steady_One_S13]

What would be my best way of testing for seeping? Other than the compression test that I already did?
Would there be any other symptoms if it was in fact the head gasket seeping?
Thank you

Try the dye test using fluorescent dye, and then shine an ultraviolet light on the system; rad, hoses, block etc. Check for a cracked or warped cylinder head. This requires taking the head off and visibly checking for anything out of the ordinary. Check w/ the FSM on the process of checking a warped head. My 2, g/l.

[DannyChaos]

I am trying to avoid pulling the head if I don't have to.I understand what your saying though and it makes perfect sense.I just do not understand how the car can run fine for long periods of time showing no signs what so ever of a coolant issue than out of nowhere for no reason at random over heat only to go right back to fine after that.I want to say it seems like air in the system,but I have bled the s*** out of it.Unless there is a head gasket leak the is forcing air into the system the whole time its running making an air pocket that ends up sitting in front of the stat.
Im lost.I have worked on cars most of my life and know my way around um pretty well,but this is messin my head up.Thank you.

[Steady_One_S13]

The smallest leak in the head gasket can wreak havoc. How's the water pump?

[DannyChaos]

Water pump is less than a year old with less than 6 months of use on it.I know the rad cap off trick to see if the coolant is moving but with this rad I don't see a whole lot of movement.So your saying die down into the cyl, pressurize it and see if the die ends up in the coolant correct?

[Steady_One_S13]

Add to the rad, run engine and check for any leaking dye using a fluorescent light. You can also pressurize the system using air at the opening of the rad.

[DannyChaos]

But that would only show me external leaking unless I ran it and pulled the head right after.Can I not just do a compression test on each cyl and watch for bubbles in the coolant? Or run a die down in the cyl pressurize it and see if the die makes it to the coolant? Im not trying to half a** things I just do not want to put the cart before the horse and pull the head only to find out that it was a 15dollar part that I some how over looked. Thanks again man.

[Steady_One_S13]

I never tried putting dye into the cylinder. But try the compression test first.

Something has to give. G/L.

[DannyChaos]

Will do,thanks

[DannyChaos]

Compression test done.
Cyl 1:170psi and holding
Cyl 2: 170psi and holding
Cyl 3: 175psi and holding
Cyl 4: 175psi and holding
Plugs looked clean and even on all four cyl.
No air bubbling out of the coolant while any of the cyl were under pressure.
So again,Im at a loss.
Dan

[DannyChaos]

Is there any way for a water pump to work intermittently? hahaha dumb question but thats about all I can think up.
I know that the cooling system is clean and clear..I flushed the F out of it,all of it.

[Second Shadow]

if your pulley and/or belt was in crap shape, or the belt was loose, it could be intermittently slipping. I would think you would notice that kind of thing pretty quick though....

[DannyChaos]

Forget that idea than,belt is new,tight and everything is turning..

[Agent]

I'd change the upper and lower hose. Very cheap, very effective. Willing to bet the leak is there.

[sldewyz]

what kind of fans are you using....are they electric? if your driving and its not over heating it might be cause by the movement of air againts the radiator. check and see if your fans are still working good. and if your using the factory clutch fan make sure you use the factory fan shroud. are you seeing any leaks of coolant anywhere on teh outside of the motor?

[DannyChaos]

The car is 100% stock. The whole cooling system other than the rad has been replaces with factory parts.
hoses,water pump,gone through 3 thermostats..boiled the last one and it opened,fan clutch,sensors etc etc etc.
Whole cooling system has been flushed and is free flowing.
Car is not losing any coolant. Has no leaks what so ever.
I am just about ready to pull the head and chalk it up as a bad head gasket.
I have none of the tell tale signs of one though. No fluid mixing or burning. No major loss in compression other than cyl 2 being about 8psi under the rest that are holding for up to a half hour under a compression test at 165psi.
The over heating is happening more often now and takes longer to cool back down. I know beyond a shadow of a doubt that it is NOT air..I am still at a loss and so fed up it's unreal.
Let me know what you guys think and thank you all for your ideas.

[sx moneypit]

You have all the symptoms of a head gasket that is seeping.

Pull the head .I believe you will find your problem.

[fallingxlove]

hey im having the same problem.
just bought my car.
and it randomly over heats then after liek 2 seconds it goes back to normal.

sometimes when i shut the car off u can hear coolant boiling back into the overflow. coolant looks kinda dirty.

did u ever figure out what happend if u ever fixed it let me know

[nigel34]

I Have the exact same problem... its been going on for about 2 months, and the more i drive it the more often it happens and the longer it takes to cool down. Im very confident its air in the system because when i stick a straw in the upper hose where it comes to the head, only air comes out. So im not even sure if the block is actually overheating, may just be when the bubble passes the sensor. But every time i bleed it it gets better with no issues for a day or two, then it starts back up. Really frustrating >< can you have a hole in the radiator that doesn't leak? only lets air in? i know a dumb question but air is getting in somehow.... No other symptoms of a BHG, compression is even.

[dgms240]

what condition is your radiator in? i noticed you said it was the only thing that hadn't been replaced. sometimes they get corroded on the inside, you may have crap in the radiator that is blocking coolant flow part of the time. i had the same problem on my old s14 (random overheating, boilong over coolant res, hot upper hose, warm lower, etc.), after flushing and burping who knows how many times and checking the stat i switched out the rad and the prob disapeared.

[nigel34]

I probably should replace my radiator. it is somewhat new... 3 years. but i had the motor sitting with just water in it for a wee bit. would that still cause it to jump so fast, it takes about 5 seconds for it to get super hot. and about 3 for it to cool all the way back down.

[youngun21a]

Does it still get hot with out the thermostat..or you haven't tried that yet..

[nigel34]

I have tried that and it runs fine without the thermo, but it never gets up to the operating temp it seems.

[nismoracingsx]

ha ha, I run w/o a thermostat as well..I do believe you have a slightly leaking hg. But, on the brighter side, i've been driving w/o a thermostat for like....1.9 years? Have yet to pull the head, lol. Car runs great.

One more test you could test is the gas test on your cooling system..you get the little plunger tube and fill it w/ the chemical and stick in into the rad neck while running and it will change color if combustion gases are detected. Kit is cheap and quick to use..GL

[SullivanRacing06]

you can also drill two 1/8th inch holes in the center of the thermo to allow it to get up to operating temps and but still slows the coolant so it dosent pass thru the rad to fast,