How would I check to see if the head is damaged?

[newton22]

I did a quick search, didn't find anything.

I'm looking at a 2001 530i that I really like. The current owner is a certified BMW tech and he said that the previous owner had driven it until the car overheated (not surprised, just negligence of replacing the cooling system). He took the engine apart and replaced the head gasket and said that the head looked fine. I looked under the oil cap and dipstick and found no sign of any milky substance or anything that showed damage.

So, obviously without taking the motor apart, how could I tell if the head or any other other internal component has been damaged due to overheating? Can valves and seals be damaged due to overheating?

Edit: I drove the car and the engine pulled fine. No noticeable issues.

[Jackcat559]

Have a compression or a leak down test done. The shop can interpret the readings for you.This will tell you the general condition of the mechanical components.

[newton22]

Okay, yeah I was thinking about getting a compression test done.

I don't know too much about these tests. Should have either one done or both done? Would either tell me the general condition of the components?

[Jackcat559]

A leak down test is similar to a compression test, but more though. They will come back with hopefully numbers +/- 7 psi max, around 160 psi. An older engine can have values as low as 140 psi. This is not great, but as long as all 6 cylinders are in the same ball park it's technically OK.

The shop doing a leak down test will be able to determine weather the piston rings are worn, valves are bad, or the head gasket is compromised.


At 156,000 my 2003 530 ran great with numbers ranging from 142 -167psi in the cylinders. The test let me know if I was going to be a responsible owner I needed to address the issue. Nothing could have happend for a few years, or maybe tomorrow.

[newton22]

Well, since he works at the dealer, I called the owner and told him to have a compression test done for me. He said that BMW charges $300 for a test (sounds steep) and that he'll do it for me for $100.

160 psi sounds low to me, but we'll see. I am too, more concerned that the cylinders have consistent numbers.

And hopefully he's not a shady mechanic who would make up the numbers. Any way to check?

[Jackcat559]

$250 to 300 at the dealer sounds about right. No way to check to see if the numbers are made up, besides standing over his shoulder. The minimum compression specs are 142-156 psi with a variance of 7 psi