today i was driving my mustang (67 289) on the highway. i took it a little farther out than usual and was going around 60ish...i noticed the temperature started slowly rising and finally i was able to get off the hwy and pull into a parking lot. i killed the motor and popped the hood and everything seemed ok...the temp gauge however said 200 then two minutes later it said 220...usually it runs at 189ish. i then checked the dipstick and noticed the oil was kinda milky. should i automatically assume i have a blown head gasket? i ran it with the radiator cover off for a bit, and it ran at 195 the entire way home, which is better than 220 at least. does anyone have any ideas? thanks

 

do a cyl. leak down test

 

how exactly do i do that?

 

Do not run the engine anymore, or you risk seriously damaging the engine. You've got oil and coolant mixing somewhere. Could be head gasket, could be a cracked head, could be intake gasket or cracked intake. You need to figure out where the leak is, fix it, and change the oil a couple times before you drive the car again.

Pull the plugs and start with a compression test. Follow up with a coolant system pressure test and leakdown test. Unless you have a compressor, you're not likely to be able to do the leakdown test by yourself.

 

ok ill do that, i checked the oil today and it just looked kinda dark, idk if there was definitely coolant in there or it just started breaking down due to the heat, i am going to drain it to check...i still have some marvil mystery oil in there too so its all gotta come out

 

water will settle out of oil (oil is lighter than water)

so if you havent run the car since it overheated then you should be able to unscrew the oil drain plug while keeping pressure on it, hold the plug in the hole so that a little oil can come out

if there is water/coolant in there then it will drain out first