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1999 Corolla Code P0171.

by Bad_dude, October 19, 2013

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It would help a bit... Which state are you in, and what's your normal January temperatures? Have you tried high mileage oil yet? Although its viscosity is higher, Mobil Super High Mileage 10W-40 has a pour point of -38F... Any news on the Delphi IAT sensor?


I live in Orange County California. The Delphi IAT is a lost cause. Plus the code was fixed. It's was the injectors. I was using the oil that you listed and from Walmart too, where it's cheapest. Then the last oil change I switched over to Mobile One Full Synthetic high Mileage oil b/c of the rebate sale. Do you think that would cause the leak worse or consume worse? But I bought the 5 Qt Jug.

Now I used the Penzoil Platinum b/c of the rebate sale.

Should I switch back to the dyno one you recommended?


Some have slowed their oil consumption by going the other way - running a thinner motor oil viscosity. The idea behind that is if the oil control holes are not completely clogged, the thinner oil will be able to flow by and effectively wiped from the cylinder walls.

Some have had really good luck running diesel engine oil - like Delvac or Rotella. Those have a very stout additive package, that is tailored to help with metal on metal contact. The only drawback I see with those oils is their higher levels of phosphorus, which will shorten your catalytic converter lifespan. Usually a non-issue, but since you are consuming oil - you risk poisoning the converter much faster than normal.

Since yours sounds like the catastrophic amount of oil guzzling - if you are set on replacing it soon, just top off the cheapest oil you can find. At this rate, additives may not help you much - time to save as much cash as possible.

Assuming that you've already tried piston soaking and similar methods to try and crack those deposits out of the oil return holes.


I am debating whether this car is still worth keeping. Maybe any other used car is better.

Depends on your pain threshold. The 8th gen Corolla is a pretty reliable machine, aside from the EVAP issues that some have and the excessive oil consumption in others. Some have opted to fix the oil consumption by rebuilding the engine - running anywhere from $300-$400 for a re-ring, to as much as $3000 for a new or reman engine swap + warranty.

Could always get luck with a different used car - all depends on what you looking at and what is available in your area. My person record has been pretty decent so far - but I've tried to stick with ones that tend to be less trouble prone to start.

If you want to start with a Toyota - an option is to trade it into a 9th gen Corolla - as pretty much any tools, knowledge, even some parts you picked up on the 8th gen can be directly put onto the 9th gen.


I think I found the leak. Currently, I have to top of the car about one quart per week. There's no leak on the floor I know there's a leak by chain tensioner and the timing cover. I have photos below and the photos of the spark plugs. The mechanic keep saying that the car burning oil and the plugs have at least 2000 miles on them. I don't think, base on the way the plugs look, it's not burning oil. I will let you guys look at the photos and give me some ideas.

I also notice the power steering high pressure hose is leaking also. Any DIY and is it hard to replace the hose?



Timing chain tensioner leak.


Front of timing cover leak. The photos above, might have leaks also on the timing cover but the rear.


Spark plug condition.

Yup, chain tensioner leak - I don't I've yet seen anyone make it past 100K miles without changing that o-ring / tensioner.

Power steering hose DIY - I think I saw one one TN, possible there is one on here. Never changed one on the Corolla, so I can't really help out.

Plugs aren't too bad. The pic definitely shows oil consumption issue, but not really bad, yet. Plug is still able to self-clean, so that is a plus. Color on ground strap looks good as well - right in the middle where it should be.

My original timing chain tensioner o-ring still isn't leaking on my Canadian made 2004 at 179,300 miles, and I already removed and reinstalled it twice when I checked and adjusted valve clearances... You can replace just the o-ring if tensioner is leaking oil.

Follow steps 20, 31, and 36c only:

Toyota o-ring part # 90301-22013

O-ring dimensions are 22.4mm ID X 3.5mm thick (29.4mm OD)... You may find one at local hydraulics supplies distributor.

After you fix your tensioner leak, your 1 quart of oil consumed per week may be reduced to about 0.9 quart per week, then about 0.8 quart per week after you also fix timing cover leak.


Hey Dom,

So with the two fixes, 0.8 quart per week isn't that much less than a quart. So the oil loss isn't much from the leak but rather from the oil burning? Should I run thicker oil to slow it down? How about those oil additives would they help?


Wow Dom, that's incredible amount of life from the o-ring on the tensioner. I'm betting that you removing it in checking valve clearances actually extended its life. When I replaced mine, it wasn't touched in almost 130K miles, the o-ring was visibly distorted when I removed it.

Bad-Dude - be careful when playing around with oil viscosity. Depends heavily on how the oil is being consumed. Thicker oil might slow down the oil consumption, as it naturally resists being burned off, but it has a side effect of clogging those oil drain holes even faster. Quite a few owners on other forums have resorted to running thicker oil to help slow consumption, only to have it suddenly start guzzling oil.

Another option is to try running a thinner oil and break up those deposits around the oil drain holes. Of course, this assumes that the holes are not completely clogged with deposits and that the cylinders are not too scuffed up. Some have gotten really good results with piston soaks to help break up those deposits - some having to run MMO or Kroil to help break those deposits up.

Same with oil additives - anything that is to added to the crankcase is hit or miss. Some have had luck with Lucas and MMO. Some swear by Auto-Rx, to which I actually had to tried out and see for myself ($26/bottle) - results were disappointing, found that it did squat. Engine deposits are too variable in composition - there are some that Auto-Rx will readily dissolve and some that it cannot. It will also swell up certain seals, depending on their composition - which is not unheard of for any solvent, but something to watch for in certain cases. Seems to work best if it stays in constant contact with the surface to be cleaned, but in an engine - much of the lubrication is splashed on components, which doesn't give this solvent much seat time to work.

Something like MMO (~$3-$4 a bottle) IMO, works as well if not better. I'd even use a flush over Auto-Rx - sure it would be very aggressive, but I'd also understand it better.


Hello Fish,

What's MMO stands for? What would you do in you were in my shoes?


MMO is Marvel Mystery Oil... I'd just trade it for a new 2015.


MMO is Marvel Mystery Oil... I'd just trade it for a new 2015.
So how to use this stuff? Do I add it to the engine, run it a little bit then drain and replace oil or just replace one quart of the oil change? How well does it work in the gas tank?



Added to gasoline, diesel, or engine oil... It's also used for piston soaks. ATF works as well.

Have you tried high mileage oil?


I am running Mobile one high mileage oil. That burns just as fast. I am thinking of 10W40 Maxlife blend since Walmart doesn't have full synthetic Maxlife 10W40. How's the brand Rotella T6 full synthetic brand at Walmart? It's just a few dollars more than the Maxlife blend.

As for ATF, what's in it that would work to clean the motor? Some on suggest in the link below.


ATF is high in detergents, and a bit lighter in viscosity... I sometimes add up to a quart of ATF as a crankcase cleaner, without overfilling just before an oil change to clean dirty engines. An Italian tuneup helps as well.

Rotella T6 5W-40 is better suited for diesel engines.

Try Castrol GTX High Mileage Part Synthetic 5W-30 oil. Its viscosity at 100°C is relatively high, while your Mobil High Mileage is relatively low. Pennzoil High Mileage 5W-30 is also excellent if they have it in stock.... As Fish mentioned, 10W-40 may be overkill.$File/BPXE-9TFDD6.pdf

Bar's Concentrated Rear Main Seal Repair- Stops all oil leaks-


If 10W-40 is overkill, Dom, why did you recommended in your post #51? Lol.

Would the Rotella T6 5W40 reduce the oil consumption?

Do you think the ATF, being high in detergents, cause the leak in the power steering hose?


It may be overkill... It'd be better to free up the rings and piston oil holes.

Not really. T6 is better suited for diesel engines. I'd try high mileage 5W-30, 10W-30, or 10W-40 instead.


Do you ever give your engine a good Italian Tuneup? Wide open throttle to as high as she will rev?

Once you're due for an oil change and 1 quart low, throw in a quart of ATF and give it the ultimate Italian Tuneup... Drain the oil, change the oil filter, replace your timing chain tensioner o-ring, throw in a bottle of Bar's Concentrated Rear Main Seal Repair, and top it off with Castrol GTX High Mileage 5W-30.


What's an Italian Tuneup?

The car only consume oil recently about 3 months or so. Before that it barely consume any. If I remember correctly, since I started using the high mileage Mobile one Synthetic.


Italian Tune-up - make sure the car is fully up to temperature and run the nuts off it on the highway. Lots of WOT (wide open throttle applications) can also couple it with some engine braking (ie, put car in 2nd gear, run it up to redline, let off the gas and let it coast down, repeat).

The basic premise is to put the engine under load, preferably under WOT conditions. Really helps blow off any deposits in the engine, running it under heavy engine braking can also help loosen some deposits around the rings.

I agree with dom, for high mileage oils - pretty hard to beat Valvoline Maxlife High Mileage and Castrol GTX High Mileage. They run sales on them from time to time - good idea to stock up when they do.

There are a lot of good articles on TN on piston soaking. For some owners, it completely reversed oil consumption - others it slowed it down considerably. For the unlucky ones that didn't seem to get it to work, nothing short of a engine rebuild will fix oil consumption. Might be worth a shot to do some piston soaking - if are lucky you have a chance to slow this down long enough to get you to a new car.

As for oil consumption starting with the switch to Mobil 1 HM synthetic - probably just coincidence. Lots of the owners reported that their cars were running perfectly, no to little oil consumption - then almost in an instant they found themselves 2 quarts down on oil.

What's an Italian Tuneup?

The car only consume oil recently about 3 months or so. Before that it barely consume any. If I remember correctly, since I started using the high mileage Mobile one Synthetic.


See my first link in post # 69.

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