300SDL Idling 10 months after runaway
 

Well, my dad and I finally decided to start the car up after it had been sitting in our driveway since December, when we replaced the shut-off valve damaging the IP and causing the engine to runaway for about a minute and half. The IP was replaced, and when the mechanic started the car and let it idle, the cooling system started to pressurize very quickly. So either the head is cracked, or the head gasket is blown; since the car still has all 270,000 miles on that #14 head, it wouldn't be surprising if the head was trashed. The mechanic was leaning towards head gasket, but we won't know unless we pull the head. Anyways, here are a couple videos of the engine running.

OM603 after runaway - YouTube

http://www.youtube.com/watch?v=eIjoMHpZtPo

Edit: Cooling system still pressurizes. A lot.

Any thoughts?

If the engine was performing fine without excessive cooling system pressure prior to the runaway, it;s unlikely that the runaway cracked the head.

The mechanic is probably correct in that the issue is simply a head gasket.

However, the head could also be cracked from a previous overheat and the limited symptoms wouldn't manifest themselves to a point where the owner takes any action.

As mentioned, it's all conjecture anyway. When you remove the head, you'll have your answer.

Before the runaway, the cooling system worked perfectly. The car ran great, except for it couldn't get out of it's own way power wise.

The car hadn't been overheated in a very very long time, so that isn't an issue. One thing that concerns me is the sound of the engine at idle.

The head is going to come off soon, and I'll post the updates on that when it happens.

Yeah, I dont like the way it sounds either. Good luck with it. They're called "rod benders" as water doesnt compress, so don't take any chances!

My hearing is poor but I don't pick up anything more than a lazy lifter once it's warm.

If the head isn't off yet, hook up a mechanical oil pressure gauge and compare with Jeremy's readings. Do you have oil analysis results from the past for comparison?

Sixto
87 300D