Oil disaster puzzelah

[MichaelP]

About thirty years ago, I forgot to replace the oil cap on our Citroen 2CV after adding oil. It was a messy and impressively smoky mistake I swore never to repeat.

Until I did it again yesterday on our '91 328ic (m42). Oil friggin' everywhere under the hood and real-time rustproofing along the underside of the car. Stupid.

I was about 15 miles from home when the smoking exhaust manifold made me realize what was going on* and I pulled into the next driveway I saw, which happened to be a tiny auto parts store out in the middle of nowhere. It was pretty much a pick up truck and farm equipment shop, but the two guys there were great, and got me a one-size-fits-all gas cap for an oil cap, some shop towels and a quart of Mobil1. So I cleaned up as best I could and headed for home.

After a mile or so, the temp gauge rose to the 3/4 mark and hung there for several miles. Distressing, but not the end of the world. Yet. Then all hell broke loose. Sizzling noises started inside the dash, which I assume was oil on the heater core, followed by smoke (steam?) rolling out of the exterior vents at the base of the windshield, and the temp gauge headed into the red. Crap.

Shut her down and rolled to the side of the road. Smoke continued to waft out of the steering column into the car and the vents. AAA'd her home (flatbed!).

I'm at a loss where to start with this. First of all, why did the car overheat? Would oil getting to the heater core do it? Maybe it wasn't actually overheating -- maybe oil on the temp sensor made it read false? Should I Gunk and gently hose down the engine compartment to clear out all the oil? It's a depressing mess.

Thoughts (aside from me being a moron)?

*A hose vacuum leak started a few days ago so that car wouldn't idle 'til it warmed up, so I didn't notice the lack of pressure due to the missing oil cap. Cluster@#$%.

[sh123]

Pressure test it. Sounds like heater matrix gone.

Not sure how this relates to the oil.

But that would be my first step

[colin86325]

Did you lose only 1qt of oil?  If you had spilled more oil it would suggest that the engine overheated because of oil starvation.
Perhaps one of your belts (for your water pump) came loose due to slick oil?

[MichaelP]

Pressure test: There was no major loss of coolant, aside from a little bit that expanded out of the overflow.

Oil starvation: Less than a quart of oil was lost. The dipstick read about a quarter way above the low mark when I stopped.

Water pump belt slippage: That's a great idea - hadn't thought of it.

Thanks for the ideas. I'll get under the hood tomorrow after I stopped being pissed off.

[MichaelP]

Well, it appears the heater matrix is broken somewhere. Idled it up to operating temp today, and there were hissing and spitting noises coming from inside the dash and vents. The temp gauge rolled just past the 3/4 mark when I shut it down.

I don't know what the non-catastrophic  oil loss had to do with the matrix blowing, but there it is. Also, why would a compromised heater matrix cause the car to overheat? Pressure loss in the system? The coolant system is full.

In case this matters: I recently R+R'd a failed t-stat, drained the non-BMW coolant that was in there, flushed the system (including the removal of the rear plug), filled it with BMW coolant and bled it. Worked great for about 100 miles before I @#$%ed up with the oil cap.

[sh123]

I might be going on a tangent here(cant say much without looking at the car personally). but i previously had a land rover v6. cant remember the symptoms but it had a headgasket fault. and it blew the resevoir bottle twice. im thinking your heater matrix.

If you have the tool do a quick compression test on the engine to be on the safe side.