Compression On Yaris 1.0

July 19, 2015

Hello guys

Yesterday i got a Yaris1.0 2000 year.

The compression on all 4 cylinders is 10atm. So..i think its low for this engine but im not so sure. The car have 155 000km. on the odometer. The top speed is about 160km/h and i really like the car. Im just worried about the comression..

Sorry for my bad english, its not my native :(

Best regards, liceto !

July 20, 2015

Did you do a wet test as well, example: couple of squirts of thin oil down the plug holes, spin it over a few times and test again. If there is a big increase in atm then it's likely that the bores and rings are worn, if there is little or no increase then look to the valves, they may be badly seated because of carbon.

If the valves are the problem then start the engine, keep it at a high rev and poor some thin oil slowly down the throttle opening until it starts to choke, stop the oil and give it even more revs, this is known in the trade as a "liquid decoke", it breaks the carbon from the valves and helps it seat again. You then do a dry test again and see if the atm has increased.

NOTE: make sure you are in the open air when you do a liquid decoke as the smoke from the exhaust is quite a lot. Also when you drive it again it will smoke for a few Kms.

July 20, 2015

I believe the compression ratio of the Mk1 petrol Yarisuseseises is 10:1 so that'd be about right.

The only engine that isn't is the diesel, which is something like 17.5:1

July 20, 2015

Thanks for the replies guys ! I will do a wet test as soon as possible.

@Cyker: Yes the compression ratio of this engine is 10:1 , and i was thinking it should have at least 12 atm. in the cyl. , but maybe im wrong about this engine :) The engine start perfectly in the cold weather, no smoke from the exhaust either. Some guys said to me , that this car can go to 180km/h , but i dont really believe this - its 1.0 after all :) So i should think that the compression is good ?

Best regards , liceto !

July 20, 2015

Thanks for the replies guys ! I will do a wet test as soon as possible.
Yes the compression ratio of this engine is 10:1 , and i was thinking it should have at least 12 atm. in the cyl.

A normal PSi test for a low Kms car would result in 170 to 200 as the norm (12 to 13.5 atm) as yours has done a lot more Kms, perhaps 11 atm would be a good result.