MMO Piston soak Prius

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Hey everyone I'm chasing down a misfire on my wifes 2011 Prius. The issue is oil is getting into the combustion chamber and is coating the plug causing no spark/misfire. P0303 is the code. The plug looks like someone dipped the electrode/threads in a vat of oil. It's coming from underneath the plug so not an easy valve cover gasket fix
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. That means it's one of two things. The valves or the rings. I tried doing a piston soak on cylinder 3 only and still no go. I pulled the denso plug on cylinder 3, poured around 4 oz of MMO, let it sit overnight, came outside the next morning, looked down the spark plug tube, and the piston was bone dry. That means the mmo leaked past the piston. I cranked up the engine (with the plug out on cylinder 3) with a rag above the hole to see if any mmo would splash out and nothing. Is it normal for MMO to leak past the piston in 8 hours or so?
 
Prii are known for oil consumption as they get older - Toyota isn't really acknowledging the fact but there's reports of the 3rd gen cars using oil at lower mileages. The 2nd gen cars will start burning oil around the 150-200K mark. I suspect the piston rings and lack of engine braking are causes of this.

How many miles? If you're still within powertrain warranty, might be time to have the dealer document this and do their own oil "consumption" test which involves topping off and placing tamper seals on the oil cap and dipstick for 1000 miles. Rings don't create a perfect seal. 8 hours is a long time, if it runs out within minutes with MMO or any oil you have a problem.
 
Sounds like she's using oil at that age. Nothing you can really do except find a good used engine from a wrecker(not a pick and pull) or rering the engine. You can try a thicker oil to slow down consumption, my 2nd gen uses less oil on M1HM.
 
What is the condition of your other cylinders? If the problem only exists in one cylinder, I would possibly suspect a stuck ring and would consider trying more MMO. Check the spark plugs from the other cylinders, if they aren't looking to good, then it's probably time for some major work.
 
Hey Kool it's just cylinder 3. The plugs foul crazy quick on that cylinder. The plugs on the others have no issues. Should I do another piston soak with mmo at the tail end of this oil change even though mmo is already in the oil?
 
Try BG 109 or BG EPR

I had great results unsticking some audi rings that were seriously gummed up.

Amazon or ebay are your best bet.
 
Hey Nicholas I'll try that at the tail end of this change. Right now we are just keeping an eye on the oil level and color.
 
Probably coked rings and plugged oil drain holes in the piston, same as with many other Toyotas (e.g., 2007-10 4-cylinder Camrys) and others susceptible to that problem. What kind of oil has been used in it? Change intervals?
 
Originally Posted By: Rtstrider
Hey Kool it's just cylinder 3. The plugs foul crazy quick on that cylinder. The plugs on the others have no issues. Should I do another piston soak with mmo at the tail end of this oil change even though mmo is already in the oil?

In that case what I did was run Lubro Moly's engine flush with the car in maintenance mode for 20 minutes. I then changed the oil with Castrol Edge HM, the oil usage got better. About 500 miles out from an OCI, I ran a pint of MMO and changed the oil when it was time. This time I used M1HM and I saw a marked change in oil consumption.

I think running MMO in the oil will help it do its work longer than a piston soak. The Lubro Moly flush works in the same concept as BG EPR 109.
 
The car was new to us as of March this year. The previous maintanence was all done at the dealer. Since we have had it it's been on mobil1 0w20 for a 10k mile change (dipstick was bone dry but that was the recommended interval I found online), the next 2 changes were bulk oil 0w20 from a mechanic that was troubleshooting this issue for 5k miles, mobil1 0w20 high mileage for 3k miles untouched, piston soaked and ran a pint of mmo for 1k more miles. Oil was drained and it's now on 3.5 quarts supertech 5w30 high mileage and 1 quart mmo. This change is going to be run to 3k max or when the oil darkens (which ever comes first). The first mechanic supposedly did a compression test and said it looked good. The plan was to run mmo for the next couple of oil changes to see if that helps. I don't mind doing an oil flush at the end of this change. I had eyeballed kreen due to previous reviews on bitog but I'm game for bg and lubro moly if those are just as good.
 
With that kind of oil showing up on the plug I would suspect the rings are so bad in the cylinder that it would show much lower compression and if it does no matter of quick fix it going to solve the problem other than yanking out the bottom end and putting new rings in. If compression is fine suspect the valve seal is the culprit on that cylinder and that isn't an easy fix. You could try High Mileage oil in that situation.

I also wouldn't use thicker oil especially in a Prius if the engine isn't running all the time. (Not sure if that is the case with your model).
 
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Originally Posted By: CT8
Originally Posted By: andyd
Have you done a compression test?
This !


I agree with this, heavily coated plugs usually indicate poor combustion pressures. Or possible bad carbon buildup causing too rich inside that specific cylinder.
 
I have some bad news for you. I would get the head gasket checked. The gen 3 prius (2010+) are well known to cause misfires when the head gasket starts to fail. Check the prius forums, it is well documented. I have a 2011 prius and I am nervous about it.
 
You can try a relative compression test, but judging by the symptoms and what you have tried so far, I would plan on installing a used engine.

No amount of snake oil is going to solve the problems that you are experiencing.
 
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Start running a (copper) hotter plug like an autolite 3926 and Rotella 10w30... and bide your time.

It also wouldn't hurt to get on it once in a while, lots of people baby their priii trying for MPG but a good italian tune up helps shake things loose with increased cylinder side pressures.
 
I ordered the BG 109 and it should be in next week. I'll try that next weekend. Im afraid this is most likely something mechanical but figured I'd try the easy stuff first. If we go the copper plug route after this should I change all the plugs to copper or just cylinder 3?
 
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