Period. Don't put anything heavy on them. They are ok, maybe if they are new, but if they've been in the weather or through cold winter, there are cracks in them that form, which can lead to sudden failure. Wood blocks are much better.

I made some wood ramps out of 2x6's that are heavy, but really solid. I have four of them. Two are smaller so that I can raise the car more in the front or back depending on the job. But I use all four at the same time. I use them on a cement pad so they are level and plumb.

DS
87 300D
Northern Iowa

The term "cinder block" implies a much weaker construction material when compared to what is termed a "concrete block". I have successfully used concrete blocks for this type of auto raising duty for years. Have always used the block with the holes pointed up and cover with a 1" x 8" piece of lumber to effectively spread the load out over the available top section of the block. Remember that industrial buildings are constructed of this material and it holds up very large loads, just need to keep it in compression and not have sharp load points.

Even large wood blocks should be topped by a sacrificial 1" x 8" to prevent the main block from being split by sharp load points.

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

The concrete/stone mix blocks I have are solid as a natural rock. They weigh about 45lbs (small one) and 75+ lbs (bigger one) They're extremely sturdy.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The concrete blocks I am using are setting "holes up" and the holes are filled with earth, so even in the unlikely event that the blocks crumble to dust, the tires are still supported by 8 inches of earth.

I understand what you are saying though. If used incorrectly, for example if a lot of weight was concentrated on one point, blocks could certainly fracture.

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

I took a 14mm hex key, put it into a 14mm box end wrench, and put the other end of the wrench inside a 4' length of pipe.

Wasn't too hard with that length of pipe as a lever, but I was wondering at the time what I was going to do if I twisted the plug out of it's threads

Of course I had it sitting on jack stands plus a floor jack, and the wheels chocked.

But it worked out just fine. So fine that I did my other car shortly afterwards.

- Patrick

__________________
1982 240D. 198k, Marine Blue/Blue, 4 Speed, Crank Windows, No Sunroof, No Rust, No Oil Leaks
2001 TDI. 197k, Lagoon Blue/Black, 5 speed, Chip, G60/VR6

Jeez... they're that tight? Looks like I'll hose them down with some penetrant first and perhaps add some heat to the mix to help.

The quart of Syn diff oil I have has been staring menacingly at me for about six weeks now.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]