I am curious about how to properly do this and not get falsely high numbers. A recent experience with a local JDM importer ended turning out not so great. They gave us, my brother and I, very high numbers which according to the FSM are higher than even possible with a new engine. Their process is to fill the cylinders with transmission fluid prior to doing a compression test. Once the engine was in our possession my brother did a leak down test and the BEST of 6 cylinders had a leak down of ~42% and I think some others were in the 80% area. I was pretty much told tonight that my brother “did the leak down test improperly” and I personally know both peoples background and experience with cars and believe my brother is much knowledgeable but figured I’d ask.
so are you talking about compression testing or leakdown, I’m confused.
Compression, I am curious cause they put tranny fluid in the spark plug holes first for every engine they test. My brother never asked how they did their test to get 180psi+ but did the leakdown himself just cause he thinks it’s a better method to tell the health of an engine. I’m just confused how the FSM says the max is 171psi, which we found out later, and he got higher and then the leakdown shows the engine is in need of a rebuild?
Them adding fluid to the cylinder bores masks ring/bore damage. They should only be giving each bore a very brief bust of WD40 to just barley lube the walls of the bore. Hydro fluid helps the bores seal increasing the comp numbers. They’re bs’ing you and doing shady work/sales by adding hydraulic fluid IMO…
COMPRESSION!
Yes a leakdown was done.
I am curious about how to compression test engines that are not in a car since you are supposed to warm it up. I guess I’m confused as to the purpose of putting tranny fluid in the engine mostly. I don’t get how an engine sold with such “solid” compression test numbers would have such poor leakdown results.
I guess I’m trying to figure out how honest these people are. Unfortunately due to certain reasons I thought I wouldn’t really have to wonder this.
Comp numbers are taken cold, LD is warm to check for ring sealing after the motor expands to it’s clearances.
I want to know how they did a comp test out of the car, unless the motor was attached to a tranny or jig with a starter motor to spin it over:ponder
It had the tranny on it
So is it pointless to do a leakdown out of the car?
no, you CAN do a leakdown teat you just won’t get the results you’d get if it were warm, when it’s supposed to be done.
a compression test can be done by just turning the motor by hand afaik
Compression and leakdown tests are best done on a warm engine, however the numbers are still fairly accurate on a cold engine. For example, an engine can test 140 across cold, and 155 across warm-both sets of numbers would indicate evenly worn cylinders/valves/etc with no apparent problems.
As far as testing out of the car, you’d have to rig up a starter to an engine on the ground/stand for a compession test, where as with a leakdown, all you need to do is find TDC on the compression stroke, which can be done by hand.
As others have said, pouring any heavy weight oil into cylinders is typically a way to trouble shoot worn rings. If you do a dry test and get bad numbers you try to narrow down where the gap is. If you pour oil and numbers are healthy then it’s the rings.
The importer just made sure that rings were not going to be a problem.
there is a lot of variables when testing that needs to be taken into consideration . like said above a comp test is done cold with no intake restrictions and so on .leakdown is better done warm so tolerances are tighter but still not a bad idea cold ,leakdown could be a worn ring ,valve burnt ,chipped and so on even a h/g leak can affect it the only reason for oil into cyl is to make a tighter seal at the rings and thats only after it failed a l/d test
Another thing to note is the fact that extra fluid in the cylinder will increase the compression which is why they got higher than normally possible compression figures.
point