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

MercFan · #1 02-23-2014, 10:04 PM

On the compression he wrote: "* I don't have the numbers right in front of me for the comp test but they came out pretty well. #1 was 320# and #2-5 were at 365+#. "

mannys9130 · #2 02-23-2014, 10:14 PM

That's kind of bad. You ideally want high compression and EVEN, EQUAL numbers for all cylinders. Even if the compression numbers are a little low, as long as the cylinders are equal across the board the engine will run well. Perhaps he's remembering wrong, or cylinder 1 has some carbon on the rings.

MercFan · #3 02-23-2014, 10:20 PM

Quote:

Originally Posted by mannys9130

That's kind of bad. You ideally want high compression and EVEN, EQUAL numbers for all cylinders. Even if the compression numbers are a little low, as long as the cylinders are equal across the board the engine will run well. Perhaps he's remembering wrong, or cylinder 1 has some carbon on the rings.

Maybe... I will need to get the actual numbers to be sure but going off the numbers he gave the variance (per my calcs) is about 14% and that's under 15% that MB gives as maximum variance - not great but still under max variance.

Another question: I don't see the blue saucer vacuum modulators that I had in my '85 - is that normal for '83?

Left Coast · #4 02-23-2014, 10:27 PM

Quote:

Originally Posted by mannys9130

That's kind of bad. You ideally want high compression and EVEN, EQUAL numbers for all cylinders. Even if the compression numbers are a little low, as long as the cylinders are equal across the board the engine will run well. Perhaps he's remembering wrong, or cylinder 1 has some carbon on the rings.

There's a number of reasons why someone else's compression test numbers are worthless to a potential buyer, as are opinions solicited on the internet. Those are not such good numbers, but they may not be very accurate either. It does look like a nice example. If you have doubts, then an independent PPI is the best way to resolve. No blue saucer in the '83.

mannys9130 · #5 02-23-2014, 11:08 PM

Quote:

Originally Posted by Left Coast

There's a number of reasons why someone else's compression test numbers are worthless to a potential buyer, as are opinions solicited on the internet. Those are not such good numbers, but they may not be very accurate either. It does look like a nice example. If you have doubts, then an independent PPI is the best way to resolve. No blue saucer in the '83.

#1 - Someone else's numbers are better than no numbers at ALL. If they are GREAT for the engine's mileage, be skeptical. If they are low, be cautious of the health of the engine and use it to your advantage if you decide to buy. If you are serious about the purchase, a PPI is a no brainer.

#2 - The op is SPECIFICALLY ASKING for opinions on the vehicle.

So why the snark?

The op posted the numbers, so I gave my opinion on what they mean if they are accurate.

Left Coast · #6 02-24-2014, 12:25 AM

Quote:

Originally Posted by mannys9130

#1 - Someone else's numbers are better than no numbers at ALL. If they are GREAT for the engine's mileage, be skeptical. If they are low, be cautious of the health of the engine and use it to your advantage if you decide to buy. If you are serious about the purchase, a PPI is a no brainer.

#2 - The op is SPECIFICALLY ASKING for opinions on the vehicle.

So why the snark?

The op posted the numbers, so I gave my opinion on what they mean if they are accurate.

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.

mannys9130 · #7 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 · #8 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.

toomany MBZ · #9 02-25-2014, 09:00 AM

Quote:

Originally Posted by Left Coast

There's a number of reasons why someone else's compression test numbers are worthless to a potential buyer, as are opinions solicited on the internet. Those are not such good numbers, but they may not be very accurate either. It does look like a nice example. If you have doubts, then an independent PPI is the best way to resolve. No blue saucer in the '83.

The blue flying saucer was introduced in 1985.