Topic: blown head gasket, what to do

[spitfire1]

I have no coolent lose oil is fine no coolent in it
 have air bubbels in the rad when running replasted thermastat
the preshure will bild and it will get airlocted  and overheat and backflow the coolent to overflow bottle
is it the headgaskit or cracted head help me
thank you
Rob

[Tr00b]

No way to tell until you take it apart. Luckily... these jeeps are pushrod engines and you won't be messing with timing like an sohc motor.They are also cast iron which is less prone to warp. They are also easy to take apart you have less bolts to remove because the exhaust and intake are shared on the same rail and are often lubricated by leaking valve covers.

If you take it apart its easy to see the gasket is bad you are safe and reuse the head.. if the gasket is OK... your head is probably bad.

[VA_YJ]

You should check the thermostat before going into the motor.  You can test the thermostat in a pot of hot water to make sure it opens properly.  Even a new thermostat can fail.  Make sure it's not upside down as well.

Look at the spark plugs.  Is one of them wet looking?  Any white smoke in the exhaust?

There is a test kit that can be used to check for exhaust gases in the coolant.  For example:

http://www.napaonline.com/Catalog/CatalogItemDetail.aspx/Leak-Detector-Kit-Engine-Block-Test-Tools-Inc-/_/R-BK_7001006_0361181638

[spitfire1]

I checked the therastat it was good no smoke out the exost and no coolent in the cylinders
 had to put a 140 thermastat with a 3/8 hole in it driled in it
to let out the air as a temp fix to stop it from air locking till I can pull the head
ps did head gaskit 3 years ago engine has 280,000 k on it did timing set 6 months ago after it whent pop in little
bits

[sharpxmen]

do you get bubbles right after starting it or only once it overheats? if the former then your assumption is correct (head gasket or cyl head), if the latter it could be a cooling issue (water pump, fan, rad plugged, thermostat - although you mentioned replacing this one you could just remove it for testing to take it out of the equation).

you could also pressurize the cooling system with the spark plugs pulled and listen for air escaping (with a hose pointed to the spark plug hole and the other end to your ear) - you can pressurize at 3 to 5 psi, don't go over 10 psi - if you see the pressure dropping rapidly then you have a leak - you can do this thru the overflow tank tube and with the rad cap in place, you'll need a radiator cap with a rubber gasket at the neck (i believe stock ones are not like that and only have a gasket at the bottom seat). If you hear air hissing out thru the spark plug holes then you got your answer.

[Jeffy]

So you replaced the thermostat and now see bubbles?  Did you purge the system when you put it back together?  Are you seeing the flow start when the thermostat opens?  The radiator will most likely overflow from the opening when the cap is off.  This will tell you if the thermostat opens and if the pump is pumping.

You can rent a coolant pressure tester.  It will attach to your radiator and you pump up the pressure and watch the gauge.  Or you could rent a compression tester.  You'll have test each cylinder to find the one leaking.

[spitfire1]

with the hole in the thermast get air bubbels right at the start
 the hole is to stop the air from billding in the head and forcing the coolent though the botom rad hose into
the rad
 with a 195 thermast with no hole drilled in it the air bilds up and it air locks and overheats
the hole lets the air out and the coolent to flow properly sow it dosn't air lock
ps new waterpump and rad replased in the past year

[Jeffy]

Are you sure you purged all of the air out of the system?  If so then pressure test the system.

[spitfire1]

ya got all the air out

[spitfire1]

did preshure test it holds constent no preshure loss

[sharpxmen]

did preshure test it holds constent no preshure loss

1. take the thermostat out,
2. make sure the coolant is flowing (so the pump pushes coolant as soon as you start the engine, you can see the coolant flowing with the rad cap off - make sure to take it out when cold and not hot so you don't get burned).
3. verify the rad fan clutch

I assume the belt is ok but i'll mention it just in case.

[spitfire1]

1. take the thermostat out,
2. make sure the coolant is flowing (so the pump pushes coolant as soon as you start the engine, you can see the coolant flowing with the rad cap off - make sure to take it out when cold and not hot so you don't get burned).
3. verify the rad fan clutch

I assume the belt is ok but i'll mention it just in case.

did all that when it overheated
thank you sharpxmen
all i can do now is pull the head and get it inspeced and hope for the best

[SamsonJR]

I  rebuilt the head on my '93 and had a hell of a hard time getting the air out after i put it all back together, on the back of the head there's a temp gauge sensor, i was able to bleed it a bit from there, then left the rad cap off over night, woke up topped it off and it stopped getting hot. You can try to get air out from one of the heater core hoses too. you need to find the highest point on the system. also, after a few days, the temp gauge was going up high again, I took a multi meter to the rad when the thermostat opened and it was right around 210, turns out the sensor was bad. Not sure if any of that helps, thats just my experience with overheating a yj

[spitfire1]

got used head today going to send it out to get checked to see if it is ok
it is from a 95 whith 250.000 k on it
it looks good but I whant to be shure it is

[RNandKT]

Just redo the headgasket, it's a very quick easy job. I took mine apart in about 1.5 hours dropped the head off at the machine shop, picked it up later and like 2 hours back together. Plus good time to replace the lifters in your motor.

If your motor has 250K miles, you might want to consider rebuilding the rest of the motor too. Mine was my wifes and only had 160K. So I was done in a few hours, spent less than $100 (including the new lifters) and it runs quiter than the motor in my Jeep that only has 80K miles on it.

Plus you should know for sure if it was a head gasket by finding the leak on the gasket.