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๐ Diagnose like a pro, avoid costly repairsโdonโt let engine leaks catch you off guard!
The ONDY TU-21 Leak Down Tester is a precision diagnostic tool designed for gasoline 4-stroke engines with standard spark plug sockets (10-14mm). It accurately measures cylinder leakage and compression, helping identify engine faults such as worn rings, valve leaks, cracks, and blown head gaskets. Featuring easy calibration with shop air and a durable carbon steel build, this compact tester is perfect for professional mechanics and DIY enthusiasts aiming to maintain peak engine performance.




| ASIN | B08225M7VC |
| Best Sellers Rank | #461,715 in Automotive ( See Top 100 in Automotive ) #3,681 in Diagnostic, Test & Measurement Tools |
| Brand | ONDY |
| Brand Name | ONDY |
| Customer Reviews | 4.2 out of 5 stars 448 Reviews |
| Item Dimensions | 11.81 x 11.81 x 1.97 inches |
| Item dimensions L x W x H | 11.81 x 11.81 x 1.97 inches |
| Manufacturer | ONDY |
| Material | Carbon steel |
| Material Type | Carbon steel |
| Number of Items | 1 |
| Part Number | 29-0629 |
| Thread Style | Npt |
| Thread Type | Npt |
| UPC | 016071508109 |
| Unit Count | 1.0 Count |
P**L
A handy diagnostic tool
I read most of the reviews. It seems that if this tool arrives undamaged then it should work. Yes, I had to change the regulator air fitting. And, yes, it's cheaply made. If you think you need a better quality tool than this, you better just pay up for one. But this tool helped me diagnose both broken compression rings and which valves were leaking. For the price, if I used it only one time, it's worth it. And to clear up the confusion, if you run 60-100 psi air TO the regulator then you should have plenty of volume to calibrate the leakdown gage, which should read 25-30 psi AFTER the regulator. Yes, the directions provided are not as clear as they could be. But these were probably written by someone with limited skills in English language.
D**H
Tester quickly identifies all types of head gasket failures
OEM makes a great line of reasonably priced, reasonably well made and reasonably accurate tools for the DIY automotive mechanic. Their Cylinder Leakage Tester is no exception. This tester has two different connection, Input air and Output air to cylinder. The Input connects to your 90-100psi shop air compressor with NPR Quick connect couplers and the Output connects to the cylinder under test a special Test Hose. The test hose has 14mm male threads to screw into the spark plug hole (hand tighten only) and a NPR Quick connector to connect to the Tester's Output port. Disconnect the Test hose to quickly calibrate the tester, then reconnect the Test hose and you will immediately see and hear results. Keep the ignition OFF. You may need to manually rotate the engine crankshaft with a wrench to bring the cylinder under test toward the TDC of its Compression Stroke so that the valves will both be shut and a "Good Cylinder" should not leak high pressure air being fed through the spark plug hole. Under this test condition, a blown head gasket will let high pressure air leak to either or both coolant passages or oil passages. Coolant expansion tanks may overflow as a result. Pressurized air may leak (and whistle?) from oil filler caps and /or Air-Oil separators. This tester can readily locate a blown head gasket that a Compression Test will completely miss.
G**G
Works good but no orifice adjustments.
Works good, but would be nice to replace the orifice size for different diameter cylinders.
C**K
It works, just read the instructions first.
I liked this product. I don't know if they've changed the instructions and put better directions in there because of what other reviewers have said, but I followed the instructions and got the job done easy.
J**S
Excelente producto
Funciona muy bien
S**0
Bad product...
I tried hooking this up to my compressor and discovered that I needed to swap out the input fitting...not a big deal. However the input fitting on the product was screwed in with some sort of permanent thread locker and the threads snapped from the body of the fitting when I put pressure on it to unscrew it. Of course, this made the product unusable. The instructions shows this input fitting to be a separate part and actually does say "not included" therefore it was meant to be removed however the thread locker insured that it stayed in place. Since I went to use the product some months after purchase, I didn't bother to try and return it, especially since I had to destroy the input fitting. All in all, I guess "you get what you pay for".
C**U
Cylinder Leak tester
My husband used it, it worked really good for what he needed on his car.
C**G
Made it work despite poor air connections
I like that this product worked (eventually), but the air connector was an ODD size. The male connector on the gauge side of the tool would not fit in the female side of either of my air hoses, so I had to squeeze the tool on the hose and hold it while a friend helped me connect the spark plug hose adapter. It was a PAIN! If I wasn't in a hurry to so the job I would've returned it for a properly fitting one but I needed to get the car back together. I don't have any idea why it didn't fit together, as you can see by the pics it looks like it should fit. My guess is the tolerance from the factory is off by list enough for it to work. Overall you get what you pay for but I made it work well enough
S**P
BROUGHT IT FOR OUR BIKE SERVICE TEAM WITH POSSITIVE FEEDBACK
VERY GOOD PRODUCT
Trustpilot
2 weeks ago
3 weeks ago