4 blown headgaskets in 7 years on same car, why?

[xirdneh]

my friend bought a tercel 7 years ago that had recently had a "crate" engine installed
about one year later the headgasket went (coolant leak)
i helped him replace it and we used a different head
a year or so later the headgasket blew again (coolant leak)
i replaced it for him and re-installed the original head
early this year it blew again (coolant leak)
i gave him a genuine toyota headgasket and he installed it
three weeks later guess what ? (coolant leak)
both of us checked the block and the head with a straight edge and feeler gauge and did not see a problem
i have done quite a few head gasket jobs on tercels over the last 15 years with nothing like this happening
any ideas?

[Notmikeb]

Does it keep blowing in the same spot? Overly tapped threads in the block allowing the bolts to loosen? Something blocking one of the head bolts so that it seems to torque down but isn't providing any clamping pressure?

[irowiki]

Where is the coolant leaking, is the important question?

[dlb]

does the engine run hot habitually?

[xirdneh]

the engine runs at normal temps after gasket change for several years at a time, until this last one which was three weeks or so of normal
when he does start having problems it's a fluctuating temp gage, steam out the exhaust and water shows in oil
i have never been able to see where the leak was after pulling a head except for coolant in a cylinder or two

[dlb]

does your friend drive the car really hard when you're not looking, and overheat it that way?

[irowiki]

Radiator fan not working right?

[Petros]

Did you replace the thermostat with a quality or factory one? that may have caused the first failure, only buy good quality ones, the communist made ones are crap. the temp "fluctuating" is a big clue the t-stat was bad.

Also, that imported engine may have high compression pistons, and using pump gas regular will damage the head gasket just like you describe. I had this problem with a "performance" 3ac I rebuilt with ported head, resurfaced block and head, and flat top pistons. I improved the coolant circulation around the exhaust valves, which is where it always failed (see my thread in the repair guilds section on head gasket replacement), and than ran ONLY premium fuel. even one tank of regular will blow the head gasket (sometimes someone would borrow my car and I tell them premium only, but when they see the cost they think one tank of regular will not harm a thing and I will never know-ha! I will know!).

you can manually check the compression ratio when the head is off by using a graduated cylinder and measure the combustion chamber volume on the head, and than calculate bore and stroke. if it is over about 10:1 it will have to run on premium fuel only. You can lower it a bit by grinding material away from the combustion chamber, but if you do make sure you do it exactly the same amount in each chamber.

The other thing might be coolant blockage in the water jacket of the block or the head, creating a hot spot.

It is very important that the cooling system is in perfect operating condition. that the rad hoses do not collapse when the engine is reved, and all the system components are operating properly.

[dlb]

the temp "fluctuating" is a big clue the t-stat was bad.

he said the fluctuating temp only occurred once the other head gasket symptoms (steam in exhaust, coolant in oil) appeared.

[xirdneh]

Also, that imported engine may have high compression pistons,

with head off can this be determined by looking at top of piston?

[Petros]

yes, the high compression pistons are flat top, with only "eye brow" valve cutouts in the top, the low compression pistons have a full "dish" top, lower in the middle of the piston crown than at the perimeter. The low compression pistons will also have the valve cut-outs, but they will not be as deep.

also, you might visually compare the combustion chamber size and shape in the head, the high compression head would have lower "clearance volume", the volume in the combustion chamber will be noticeably smaller.

[xirdneh]

i have had two different heads on the car with same result

[irowiki]

Has the radiator been replaced? Radiator hoses?

[Mark]

Out-of-calibration torque wrench?

[Petros]

good point Mark. i happened to check the calibration on an over the counter auto parts torque wrench (I put the end in a vise and hung a weight on the handle, calcuated the exact toque on it), and found it was off by over 17 ft lbs. I took it back (it was new out of the box). you can use this method to to mark exactly where 43 ft lbs is on the scale with tape (the torque value of the head bolts).