itsdaveman
Member
So I'm new to this diesel thing. Picked up an older tdi with over 400k miles on it. Previous owner kept it up but got rid of it because it's due for a timing belt, and its got coolant mixing with oil. So he called it quits. I was just dumb enough to buy it off him
I want to run a compression test to see what I can't decipher about the overall health of the engine, but I don't own a diesel compression tester, and local parts stores don't seem to have them on hand for rental. I could send it to a shop, but I'd rather do it myself for the learning experience.
This brings me to my question. From what I understand, compression ratio tells you how much the engine will increase the pressure of air during the compression stroke. Googling around says the tdi makes around 19.5:1, and if air at sea level is about 15psi, then wouldn't you expect to see a reading of about 290 psi? Gas compression testers could handle that. But searching around this forum, I see folks posting numbers in the upper 400s. Why is the theoretical pressure so vastly different from what people are actually reading? Thanks in advance for the help.
I want to run a compression test to see what I can't decipher about the overall health of the engine, but I don't own a diesel compression tester, and local parts stores don't seem to have them on hand for rental. I could send it to a shop, but I'd rather do it myself for the learning experience.
This brings me to my question. From what I understand, compression ratio tells you how much the engine will increase the pressure of air during the compression stroke. Googling around says the tdi makes around 19.5:1, and if air at sea level is about 15psi, then wouldn't you expect to see a reading of about 290 psi? Gas compression testers could handle that. But searching around this forum, I see folks posting numbers in the upper 400s. Why is the theoretical pressure so vastly different from what people are actually reading? Thanks in advance for the help.