Disco II as described in my signature. Head gaskets done 2 years/20k ago.

Yesterday I was driving in 30 degree weather in the highway in Dallas and I looked down to see my temperature needle shooting up. I pull over expecting to find a hose problem and I see a needle thin spray of antifreeze and steam coming from the passenger head gasket, spraying on the firewall. Not good. I'm away from home so I let it cool off and drove a mile to an auto store. I got 10 gallons of 50/50 antifreeze and filled it up, thinking I would make it to the hotel and hire a wrecker to get me home today. While I was in the auto parts store it made a huge puddle of antifreeze.

Today is the icepocalypse in Dallas and I saw NO MORE LEAK so I set out for home. It took me two hours to get out of Dallas at 5 mph and another hour or two down the interstate and it is not leaking a drop. Temperature gauge fine.

What the HELL? I obviously need to put a new head gasket or two in and I can manage that, but I don't know why that would happen nor why it would clear up. I have no misfires or other indication of cracked heads. Antifreeze and oil look fine and codes are clear.

Could my expansion tank cap be bad? What would cause it to be okay the next day? I'm befuddled.

 

Drove an hour farther at 75 mph and the heater went cool. Sure enough, the temperature gauge started to climb. I pulled over and now the front is wet. There is a small pool under the alternator (top of engine). I let it cool and put a gallon of antifreeze in it, which topped the radiator off. The radiator is not leaking but the top hoses have coolant on them, probably thrown by the fan. I could not see where it was coming from.

The hoses were not especially hard as I would expect if they were over pressurized.

Anyway, not good but I'd appreciate any diagnosis or way to diagnose the real problem.

 

I don't know what antifreeze you are using but some are very corrosive and have a detrimental effect on older vehicles but not on new/modern vehicles. It's worth Googling the problems with antifreeze to find out what is good and what isn't in older vehicles. I use diferent mixtures in my 20 year old Pajero to the 12 year old D2 and completely different in the 5+ year old RRS. Problem is some AF mixtures attack brass and soldered pipes, alloy heads etc whereas they are fine in later vehicles.

 

If you can not find an obvious leak, then you need to have the system pressure tested, or use a dye in the water and trace with a light. Your leak could be anywhere from how you describe....

 

I've been using Prestone (green) for a few years.

 

Are you thinking a cracked head? I have a pressure tester if you mean the kind that screws on to the spark plug hole.

I arrived home and it is wet on the front cover but even letting it idle and revving it for 30 minutes I see no stream or drip. It is bizarre.

I'll check the cylinder pressures after it cools down and after I pull the fan so I have a better view of the front. I'm sure the passenger head gasket is toast but I don't want to fix it until I figure out the problem.

The only thing relevant that I have done recently is replace the water pump. Maybe the gasket was faulty or I was faulty putting it on, the coolant is leaking, and when it gets low the steam creates too much pressure. Heck I don't know. I have another water pump gasket so I can't give that a shot too.

I checked the oil again and it looks perfect, and so does the antifreeze. I'm not a mechanic so this really vexes me.

 

I was refering to pressure testing your water system...Your looking for a water leak correct?

 

I am. I thought maybe you thought a bad head gasket or cracked head might be transmitting pressure from a cylinder to the water jacket.

Im afraid I don't know what a water pressure tester looks like or how it works. I'll Google it.

I just tried to replicate the issue by taking the fan off and driving it but it wouldn't come close to getting hot.

The upper hoses do develope some pressure when I Rev the engine but I assume that is because the water pump is spinning faster.

I can find a leak. I'll Google the pressure tester you mentioned. Sorry for my confusion. I know how to do some big things but that's the extent of my mechanical knowledge.

 

Harbor freight sells a pressure tester or you can borrow one from local parts store.
Just a little pump and caps ( for different systems) that you can add pressure with.

 

Just to mention the obvious: you are bleeding the air out of your system, right? If you did a water pump and didn't bleed, you could definitely boil over.