Looking, considering this 1983 300TD - PeachParts Mercedes-Benz Forum

mannys9130 · #1 02-24-2014, 02:17 AM

Quote:

Originally Posted by Left Coast

Without any other knowledge of how the compression test was performed, IMO, the numbers are as good as no numbers at all. Someone recently posted that his compression test showed zero on 5 cylinders, but the next day his car was running beautifully. An extreme example, but I think you get the point.

I meant no insult to you personally, and it was poor judgement on my part to quote your post to make my point. Perhaps you didn't note that I agreed with your opinion regarding the numbers, and I agree with what you've written above. What we can offer here in response to questions like this one are cautions. There have been some good points made in that respect.

Ah, I see.

The numbers aren't to be trusted 100% as correct, but if they seem like they might be right I'd allow them to sway my opinion on the health of the engine a little. I wouldn't praise the engine or condemn it on principle of the owner's numbers.

It's a little harder to do a compression test on a MB diesel compared to a gas MB. Honestly if the engine starts cold with minimal glow, has an acceptable amount of blow-by, has a nice smooth cold idle, and has great power, I'd be satisfied without doing a compression test. I bet a bunch of people are going to be upset that I say that. That's ok.

eatont9999 · #2 02-25-2014, 08:49 AM

Quote:

Originally Posted by mannys9130

Ah, I see.

The numbers aren't to be trusted 100% as correct, but if they seem like they might be right I'd allow them to sway my opinion on the health of the engine a little. I wouldn't praise the engine or condemn it on principle of the owner's numbers.

It's a little harder to do a compression test on a MB diesel compared to a gas MB. Honestly if the engine starts cold with minimal glow, has an acceptable amount of blow-by, has a nice smooth cold idle, and has great power, I'd be satisfied without doing a compression test. I bet a bunch of people are going to be upset that I say that. That's ok.

Most sellers don't like the idea of you pulling the injectors off their car and doing a compression test. I can't blame them, either. I would not want some stranger and self-proposed MB guru removing anything from a car I was trying to sell. That said, I find it quicker and more prudent to judge the engine by how well it starts and runs. I ask the seller not to start the car before I see it so I can tell what a cold start acts like. The last 300SD I bought only had one working GP but it started up nicely (in the summer) and ran very well. After purchasing the car, a compression test showed 430-450PSI. Unfortunately, the IP was destroyed by a WVO project done by the PO. The symptoms were masked by a failed motor mount.