Suddenly Loud valve noise and poor mpg and power

What was the oil level before you changed the oil?

 

I too have this problem with my 06, idling really loud at low rpm. Also my 06 burns oil, about 1 qt every 2-3000 miles. However I don't have hybrid battery issues, mine always charges up to the green level, rarely reaches purple.

On your car, the reason you don't have power is because the hybrid battery charge is low. It's not providing power to the electric motor to help you accelerate, you are mainly using the ICE engine to drive.

I would first check your 12v battery and make sure it has proper voltage. That can cause many unexplained problems.

 

Check the 12v first. If it's the original, then it has done well to last this long. The 12v is also a relatively cheap fix. Otherwise it could be the HV battery (expensive, but not as expensive as people worry).

 

Since the OP complained of an unusual sound that appears to be related to excessive valve clearance, then the obvious thing to do would be to remove the engine valve cover and measure valve clearance. If the OP wants to do that, I suggest he subscribe to techinfo.toyota.com to determine the exact procedure and the valve clearance specs.

I did that procedure on the 2001 several years ago and it is not too hard to do the measurements. You have to rotate the crankshaft by hand as you perform the measurements.

The hard part would be if you decide you actually need to change the clearances, which require removing the camshafts and replacing the bucket "lifters" which define the clearances.

You'll need Toyota black FIPG sealant and a new valve cover gasket when reassembling.

While the valve cover is off, the valve train can be inspected closely. You might also replace the PCV valve on the valve cover while you are at it.

 

Given the loss of power and the sudden onset of the noise suggest something more fundamental than just tappet (lifter) noise. Loose tappets do not usually greatly affect performance.
We are shooting somewhat in the dark. This could be an engine problem such as a broken valve spring, but why would this affect the HV battery state of charge? Unless the battery is worked hard to compensate for the lack of engine power, but battery/transmission problems may also produce the lack of performance.

John (Britprius)

 

well he's only at 95k miles, even if the HV battery would be the issue and hopefully it is, he's covered under the emissions warranty.

 

Yes, maybe a camshaft lobe or a bucket spacer has fractured, so that a valve or two is not opening. That would have a big impact on engine power. The engine valve cover would need to be removed to determine whether this is the case.

 

If you do tear it down and repair, please post what the bad part was you found. Sounds like you have it narrowed down to the top end as far as the noise in concerned.

On a different tune, your 12 volt is getting pretty weak. You will need one of those before long also.

Best of luck to you. Hope you can get it fixed cheap. One question, what kind of oil has the engine been fed during it's life time? I understand you have stayed on top of it as far as oil changes. Sorry to hear the problem, don't see this very often here on this board IIRC.

 

Mines got a similar problem; 07 @ 115k. MPGs ok and no codes. No CEL. Rough as ball bearings on idle; not noticeable at speed/accel. Is it ok to drive as is? Will the engine be damaged?

 

It is not OK. You need to have the unusual noise investigated. Further damage may result to the engine.

A mechanical issue with the engine may not produce a DTC.

 

Yes, there isn't much demand for used Prius engines because they rarely fail, so the pricing is extremely attractive. Please make sure that you are getting an engine from a 2006-2009 Prius and not one from another Toyota using a 1.5 liter engine, such as Echo, Yaris, Corolla, etc.

 

It's a shame to lose the engine under 100,000 miles. Did you buy it new or used?

 

My 2006 is similar to what you had experienced with the old engine. It seems to run ok but at highway speeds, it just seems like it doesn't have much power. It has a loud knocking sound at idle. This past weekend I drove to Las Vegas, a 270 mile trip. Normally I can get over 50mpg going there but this time around I was lucky to get above 40. Many of the hills I climbed, the engine seemed to struggle and the mileage on the mfd showed 15mpg when I was climbing. Many times when I traveled 70mph the car would show mpg in the 20s and 30s. I can't remember ever seeing that on my 2008 going the same route. Sounds like I'm going to need an engine to solve the problem.

 

Sounds like my car, how much did they charge you for a diagnosis?