98 DOHC blown head gasket. opinions wanted.

[Evan]

the LGT just bought has a blown headgasket.

• i changed the oil (of unknown age) before i bought it and saw very few, very small coolant bubbles stuck to the bottom of the oil pan.
  
• there are air bubbles coming up from the coolant overflow tank, presumably bubbles getting circulated around the system.
  
• the coolant system will build pressure as soon as you start the motor
  
• if you open the rad. cap you can smell what seems to be exhaust.
  
• the radiator hose bumps if you squeeze it, from trapped air
  
• the coolant overflow tank has a bit of a brown haze at the top of it, probably oil
  
• the coolant overflow tank fills to overflow in about 20-30min of driving.
  
• i put about 65 miles on it on the highway (70mph, normal steady temperature) and then got off, let it idle for about 5-10min, then started the 10 min rural drive home from there.
  
• it started to overheat about half the way home and i had to pull over and let it cool off about every mile.
  

i'm thinking that the headgasket blew between the cylinder and the coolant jacket. the cooling system isn't doing its job too well with all the air in the system. i'm probably going to need to drive the car to work for the rest of the week, do you think that will be ok?

do you guys agree with my analysis?

 

[Lawdawg]

I am not a mechanic, but used to work in ship engines rooms on large deisels and whatnot. Here goes, generally speaking, air is bad in water systems because water pumps can become vapor locked when air is introduced and the pump loses suction. Water then stops moving around, which can ruin water pump and engine. I also think air will affect the t-stat as air does not conduct heat as well as water. All in all, air in water systems sux and I would be leary driving around like that.

On the diagnosis, from what you are describing, yes, you have a breach in your gasket, likely causing the higher pressure from combustion to enter the coolant system, then when you are not running and things cool down, a little coolant gets into oil when coolent pressure exceeds oil system pressure. That's my theory anyway....

Short answer, I agree with your analysis. I am not willing to say it will be OK. With an air bound water pump or even close to vapor lock with intermittant waterflow, you become essentially air cooled

 

[Rightseat]

yer motor is fooked pure n simple, laddie

mixing between oil and coolant isna good. the coolant in the oil has now very likely cooked yer bearings, depending on how bad the overheating was

if'n ya donna do yer bearins when ya do the head gaskit, the motor will only lasst a few hunnert miles. ask any tech at a scooby dealer, they know this

don't ask how I learned this. was an expen$$$ive lesson -- "rebuilt" 2.5 in rally car after head gasket failure DNF, then another very expensive DNF in a rally, another cooked engine, it's a vicious circle

Dave G

find another 2.5 and drop it in, toss yer cooked one

 

[Runnah]

Put the "superman" engine in it!

 

[Evan]

keep in mind the coolant in the oil was very slight, probably as much as a beer bottle cap full in 4+ qts of oil. that's not really a concern for me. i drove it 75mi after the oil change and saw no coolant at all in the oil.

brett when you say the pump can be vapor locked you mean that it still spins but doesn't pump anything (because its surrounded by air)?

i have noticed what seemed to be a couple air bubbles going past the temp sensor, the gauge would jump up from 9 o'clock to about 10 o'clock then right back down. i've been keeping a pretty good eye on it. it stayed dead center at 9 o'clock the 4 times i drove it today (dads house and back, work and back, 20mi total).

 

[gearsoup]

Dave G

find another 2.5 and drop it in, toss yer cooked one

Put the "superman" engine in it!

Problem solved!

 

[Mr Mike]

I agree with the superman engine drop in... once you over heat some thing your just asking for problems. I could see if it was cast iron block and head (like my old fj40) but... if you just fix it your gonna be fixing it for ever..

Get the engine, we'll all help you put it in, it will be fun.

;D

Mike

 

[Lawdawg]

Yeah, that is what I mean by vapor lock. Water pumps don't like too much air. A few bubbles here and there not a problem but too much air and they lose prime then make steam before bearing/impeller fails. Sometimes can happen when you flush coolant--you need to make sure all air slugs are out of system. What is worse, as I mentioned, your t-stat will not work properly if affected by too much air or oil. Oil coat or air will affect the ability to transfer heat to t-stat, which is a problem in a cooling system because t-stat may not open when it should....

What about this

http://forums.nasioc.com/forums/showthread.php?t=965031

 

[Evan]

it looks like i'll be driving it till the weekend then i'll switch back to the red legacy.

i'll drive the red legacy till i replace the HG on the new one, then again switch back to the new one.

also, i've been thinking about the coolant flow of the whole system. the air-filled water coming from the motor enters the radiator at the top left then exits at the bottom right. it goes through the termostat and then through the water pump and into the motor, correct?

so for it to pull an air pocket into the motor, the air would need to be at the bottom of the radiator. unless the water is moving at a pretty quick CFM i would imagine all the air would quickly rise to the top of the radiator and possibly head over to the rad. cap and overflow tank (which was bubbling with air remember?) where it would basically filter its self out once the pressure became great enough.

but who knows.

 

[gearsoup]

the vapor lock could also take place in the engine........

 

[Mr Mike]

If your bubbling with air, even cold. chances are your pumping it in there via the head gasket(s). We over heated a VW golf to the point of thermal nuclear melt down at the objiway rally (spelling way off!!) and actually had cold water shooting out of the over flow when you cranked it.

but a small crack would let air get pumped in on compression stroke.

 

[rallyXcramps]

Do the head gasket and timing belt. Flush coolant. Change oil. See what you have after that. I bet it'll be all good.

 

[gearsoup]

not after overheating it several times....

 

[Evan]

well i didnt 'overheat' it, i just 'heated' it. it never made it past 3/4 the way up the gauge.

 

[rallyXcramps]

When you have the head off check for warpage on the deck and head with a straight flat bar with a machined edge on it. Put the machine edge down and use a feeler guage to see if theres any gaps. Hold it long ways and short ways and diagonal on the cleaned surface. I also use a flash light to see if light can get under the straight edge. That will tell you if things need to be decked or shaved. I bet the boxer can with stand way more heat than you gave it. WAY MORe! 8)