If the head is not milled flat (shaved) for head gasket replacement, the leak can return. I had this happen once, and have always had the heads shaved since w/ no more failures.

Another cooling system leak test is necessary. A small hose may be weeping, or the water pump leak might have escaped notice on the previous leak test.

good luck

 

Topped off my radiator, got another oil change just to flush out my system and it overheated again.

My mechanic did a test of my radiator fluid and found no exhaust fluid in it, so he says the head gasket should be working.

When I overheated, the heater only pumped out cool air even though the coolant levels were fine.

He felt the air coming out of the fans and it was cool but the hoses were hot.

I seem to be the owner of an automotive oddity, which is not awesome.

Any thoughts?

 

You're losing coolant. You need to find out why. A cooling system leak test should hold pressure:

‪How To Diagnose A Cooling System Overheat‬‏ - YouTube

Even then, the cooling system leak test is using only ~15 psi during the test. A carbon monoxide test of the coolant, which your mechanic did and what ETCG shows in the video, may be a fairly reliable way to test for combustion chamber leaks, but putting 90 psi pressure in each cylinder @ TDC and seeing/hearing if air is going anywhere (a leakdown test) is the most reliable way to determine if there's a combustion chamber leak.

 

Any water/coolant on the carpets ? Check up around the back of the glovebox are at the floor and under the dash...could be a faulty heater core. You mentioned no hot air from the heater/fan, that would be my best suggestion. Was the thermostat replaced as well ??

 

I think I found the problem, by process of elimination, and it sounds like what @Roader had.

I've been putting coolant down the radiator and within a few hours of driving it vanishes. I ran the car for hours in my garage looking for an external leak and found nothing. Yesterday we drove 9 hours to West Texas and the radiator was dry again, and my oil was milky. So it must be a head gasket leak, then, huh?

How long can I keep driving and filling up the radiator for before all that radiator fluid in the oil causes serious damage to the engine? We have another 1k miles to go. Would getting an oil change buy me some more time?

Btw, thanks everybody for all the help, it has sincerely been appreciated.

 

Did you stop during those nine hours driving to check the coolant level? It's a pain in the *** to let the car cool off for a half an hour at each gas stop so you can add water but, considering the route you're taking will probably have 100+ degree temps, you should be really careful driving from TX to CA with a leaky head gasket. I drove mine 1500 miles in similar circumstances, adding water every 250 miles or so, but I never had water in the oil; it was just burning water, not dumping it into the crankcase.

If you can't get the head gasket replaced/head surfaced/block checked in TX then definitely get the oil changed, add water at every gas stop, and keep your cell phone charged.

 

My biggest concern is water in the crankcase...It will eventually lead to burning up the bottom end/crank bearings/connecting rod bearing failure. Change the oil and check it every couple of hundred miles. Keep extra oil and coolant with you. Get the head milled and new gasket installed before you need to replace the engine block.

 

@bigpat - how do I know when the engine block itself has been damaged? Do I have to take it apart to see that or will the car begin to idle rough or lose performance?

 

Damage is mostly noteable upon teardown and inspection for signs of bearing failure on the crankshaft, connecting rod bearings and main journals. Evidence of damage while running the engine can be in form of knocking noise (rod bearing) and excessive smoke in the exhaust. Unfortunately at this point, the engine is heavily damaged and will likely not be rebuildable due to excessive wear and scoring damage to the crankshaft and possibly the block itself. The point here is to get the head milled/resurfaced and replace the head gasket now, to avoid a complete replacement of the engine block and cylinder head.