Topic: The official mileage vs. compression thread

[Lewis Hein]

We all know that our Toyota engines (like all others) lose compression with mileage. Many of us here may know exactly how much, but for the benefit of dummies (like me) who haven't been doing this for decades, I think we should consolidate some of this knowledge here. So, here goes. Please give as complete answers as you can so that the end result can be that much better. Also, let's keep it to Toyota engines for now.

What kind is it? 3RZ? 22R? 22RE? 3VZE? Something else?
What is the compression? (bonus points for listing all 4 cylinders)
What is the mileage (odometer, not fuel economy)?
Is the cam stock?
Are the valves adjusted correctly?
Edit: As Gnarly4X pointed out, you should mention elevation, too. The compression data are almost meaningless without it

If I get enough good and complete responses (Say, at least 10-20 per engine), I'll turn this into a graphic and post it here for all to see.

A big thanks beforehand to any and all who answer these 5 questions completely. Your response will contribute to making Marlin Crawler the home of the best Toyota tech in the world!

[Lewis Hein [OP]]

I would post my numbers, but... My mileage is unknown! I will, however, try to get some numbers of a 22RE of known mileage I have access to.

[cporche]

ill get some numbers at my next tank of gas, i had a lot of idles and test drive this tank, but after the auto to manual swap i went from about 12-14 to about 18. should need gas buy saturday or so.

[Lewis Hein [OP]]

Sorry if I was unclear -- I meant "Number of miles traveled" not "fuel mileage".

However, now that I come to think of it, fuel mileage would be interesting, too.

[Toybrota]

70K miles on a "remanufactured" 22R
120psi on all 4.

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[Gnarly4X]

70K miles on a "remanufactured" 22R
120psi on all 4.

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Hey Toybrota,

Did you get those readings with engine cold or near normal operating temp?  What is your elevation?

Gnarls.

[Lewis Hein [OP]]

Good thinking, Gnarls.

BTW, if you should care to. I know you've got a really nice, freshly rebuilt engine...


Everyone: We're off to a good start, let's keep that data coming in! Remember, this is information that may not be posted anywhere, so you are helping to create an original piece of Toyota tech that will be so valuable to those buying Toyotas, reconditioning Toyotas, or just wanting to know more about their vehicles.

[Gnarly4X]

Good thinking, Gnarls.

BTW, if you should care to. I know you've got a really nice, freshly rebuilt engine...

Hey Lewis,

Well... thank you, I appreciate the thought.

I "think" I have a nicely rebuilt engine, but I'm still tweaking it and have some issues I am working through.  I did not anticipate the delays and the extra costs of things not working after my truck sat in my garage for almost 4 years.

As I have mentioned many times, if you are not an engine builder or auto mechanic by profession, and just an average DIYer, you don't typically get much practice rebuilding anything on a Toyota truck.... they just don't break down that often.  So, consequently, my "rebuilding" experience with my Toyotas has been  limited.

Gnarls.

[Gnarly4X]

Good thinking, Gnarls.

Yes... gas mileage and compression readings will most likely be different from sea level to higher elevations, and for the EFI vs carb's engines.  So, if you are collecting data, the elevation that the vehicle is typically driven at should be part of the calculations...... that's just my opinion.



Gnarls.

[Lewis Hein [OP]]

Yes... gas mileage and compression readings will most likely be different from sea level to higher elevations, and for the EFI vs carb's engines.

Gas mileage, yes, although that is a side note to this thread. Compression reading is a new one on me, but makes lots of sense given that P1*V1=P2*V2 and all that jazz.

Of course, that equation doesn't apply here because the air in our engines is NOT an ideal gas, and won't behave ideally at the compression levels we expect in these engines. Off to my handbook of chemistry and physics...

Lewis

[Lewis Hein [OP]]

OK -- Back to the official thread, with an edit after valuable insights by Gnarls. Please add your elevation to your data, because it will make it so much more meaningful!

Temperature would be nice, too -- Charles' law doesn't go away because I forget about it, either.

Lewis

[Toybrota]

Hey Toybrota,

Did you get those readings with engine cold or near normal operating temp?  What is your elevation?

Gnarls.

I should've added more details.

4,200' elevation.
Engine was warm, throttle closed.
Used a HF gauge (just opened)

120 across all cylinders with no deviation what so ever.

Engine burns 1 quart ever thousand miles (doesn't smoke)

Engine was replaced with a "remanufactured" 22R short block of questionable quality at 265k miles back in 2001.

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[Gnarly4X]

I should've added more details.

Great post!

Interesting.... I'll post some comments later.

Gnarls.

[Gnarly4X]

I should've added more details.

4,200' elevation.
Engine was warm, throttle closed.
Used a HF gauge (just opened)

120 across all cylinders with no deviation what so ever.

Engine burns 1 quart ever thousand miles (doesn't smoke)

Engine was replaced with a "remanufactured" 22R short block of questionable quality at 265k miles back in 2001.

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I am sorry to read that your engine is burning a quart of oil every 1,000 miles.... I don't think that's good.

The top spark plug looks like it was not torqued and seated into the head and was leaking.  The other plugs don't look bad considering oil consumption.

Even at your elevation, 120 psi seems to be a little low.  Since your engine is burning that much oil, I would suspect you may have a cylinder/ring issue.

Gnarls.

[Toybrota]

Hope this thread doesn't die! I'm interested to see more information.

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[kneedownnate]

I will check my 91 when I can.  22re with nearly 284,000 miles, burns a bit of oil.  Very bad valve stem seals, fouls plugs quickly, but despite this it still had 185 psi minimum last time I checked

[Lewis Hein [OP]]

Hope this thread doesn't die! I'm interested to see more information.

I really hope so too. Right now, I have two data points, yours and Nate's. That's not enough to draw any meaningful conclusions.

[Lewis Hein [OP]]

I will check my 91 when I can.  22re with nearly 284,000 miles, burns a bit of oil.  Very bad valve stem seals, fouls plugs quickly, but despite this it still had 185 psi minimum last time I checked

At what elevation?

Thanks.

[Gnarly4X]

For those interested.... to calculate for the difference in elevation when reading your compression, you can use a close estimated number of 5.25 PSI lower compression reading for every 1,000 feet rise in elevation from sea level.

In other words, if your engine  (1986 22R/RE) compression is spec'd at 171 psi, and it reads 171 PSI at sea level, and your actual elevation is 4,000 feet, your compression reading will be 4 x 5.25 lbs less, or 150 psi.

Another example.... if your reading at 3500 feet elevation is 152.6 PSI, your reading at sea level would be about 171 PSI.                                                                                                                                                 

Gnarls.

[Lewis Hein [OP]]

Or if you don't like approximations, use Boyle's law

P1     V2
--- = ---
P2     V1

V1 is the volume in the cylinder at BDC, V2 at TDC. P1 is local atmospheric pressure, P2 is pressure inside the cylinder at max compression (I.E, P2 is what we measure with a compression gauge).

V2/V1 is constant with respect to altitude, and therefore P1/P2 is, too. Thus, if your local atmospheric pressure is 75% of pressure at sea level, your compression readings will be 75% of what they would be at sea level, too.

So, if you are at 4000 feet elevation, air pressure is ~12.7 PSI rather than the ~14.7 at sea level. Your compression reading would go down from 171 to 147 PSI.

This is an approximation too, of course, because air is not an ideal gas.

[kneedownnate]

At what elevation?

Thanks.

Below 1000 feet

[Lewis Hein [OP]]

Thanks, Nate.

Now everyone else, don't be shy...

[Toybrota]

Wish I had paid attention in junior year math, stats would've been nice! I know 2 different people with these trucks, I might be able to talk to them about doing some compression tests.

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[fasterspider]

I did a top end overhaul in my 22R a couple of weeks ago and did NOT do a compression test before hand because I could tell it was down a bit but, the issue was bad valve guide seals and cheap fuel.
The bad seals let oil into the combustion chambers and the cheap fuel left huge deposits on the exhaust valve seats and on the valve faces. That in turn causes lower compression to occur because the valves can't seat 100% so they leak.
I want to adjust my valves again because after the job was done and I've put a few miles on her, the valves settled in and are making noise in a few places I won't tolerate so when I do, I'll do a compression test and give you numbers.
The engine is only a two year old eBay long block and the seal failure is not surprising, gasket kits do not include quality Viton valve guide seals, they contain garbage Chinese seals that are almost free. The guys that rebuild engines on the cheap use the cheapest kits they can acquire so they can make some kind of profit, my engine cost $1100.00 delivered so there was no complaint when said seals failed.
Oil burning is a huge cause of lagging performance in any 4 stroke internal combustion engine that has endured years of on/off hot/cold cycles and rubber sitting in petroleum based fluids turns the rubber into plastic that lost its pliability.
Pliability is what keeps the oil out of the combustion chambers, lose pliability and start buying a lot of oil.
It may seem like a huge PITA and well, it is a huge PITA but, changing out the valve stem seals gave me back what feels like brand new engine performance.

[Lewis Hein [OP]]

I want to adjust my valves again because after the job was done and I've put a few miles on her, the valves settled in and are making noise in a few places I won't tolerate so when I do, I'll do a compression test and give you numbers.

Thanks, fasterspider. I will eagerly await your numbers.

[Mudder]

An important piece of info you do need is if it's mated to an auto or manual tranny. I say that because my 89 22re was mated to an auto, had 210k miles and 175 as it's compression reading

[Lewis Hein [OP]]

Here are what numbers I have for the '85 of unknown provenance:

It's a basic 22R with manual transmission
Compression: 140 +/- 2 on all 4 at 5300'. At sea level, this should be 170 +/- 2.5.
Mileage: Unknown, but see notes. Based on the history of this truck as told to me and the condition of the timing chain, either ~30,000, ~150,000, or ~211,000
Stock cam.
Valves are adjusted correctly -- this was a big help!

Notes:
First the valves. Adjusting them made a big difference. The first time I tried it, I got about 128 (155 after correcting for elevation). The engine runs better now, too.

Mileage. Looking at the plastic timing chain guides, I estimate that they have used about 1/4 of their life or maybe a bit less. Assuming "life" to mean 120,000 miles, that means they were brand new about 30,000 miles ago. This gives either ~30,000 or ~150,000 miles. Currently the odometer has ~211,000, but many of those were (supposedly) towing miles. Brake & clutch pedal rubber would suggest 150,000 rather than 30,000 (comparing to a '93 pickup of known mileage)

For good measure, here's the spark plugs, in order:

[Lewis Hein [OP]]

I promise that someday I'll get that '93 of known provenance checked...

[Gnarly4X]

For good measure, here's the spark plugs, in order:

I can't tell by the photo of the first two plugs, but the third one looks like it *may* be showing that cylinder has a leaking valve guide seal on the intake valve.  I can't see the 4th plug.

Do the plugs show fairly even carbon browning around the ceramic insulator tip and center electrode?  Or does the carbon/browning appear on one side of the ceramic insulator tip?

They look like they are firing a slightly rich mixture, which may be normal for your elevation and a carb'd engine.

Your compression reading looks right on for your elevation, and I agree that at sea level you'd probably get a 171 psi reading or very close to it.

Gnarls.

[Lewis Hein [OP]]

Carbon browning is only on one side -- I tried to photograph the brownest side on each one.