Quick "clunky" start-up.

Mine does the same thing. Check your oil level but otherwise, I suspect it is just winter gas. Speculation on my part, I've been thinking of trying a tank of 89 octane just to see if it is a winter-gas, knock. I just haven't tried it yet because it doesn't seem that big of a problem.

Bob Wilson

 

Yup, mine sounds like that whenever it's really cold. Thought it was the gummy throttle plate but now I agree with Bob. Been doing that now for four years. Just had 120,000 mile service and got away clean. I have had other non-hybrid vehicles that had similiar "clunky" starting symptoms. So enjoy your ride.

 

87 octane fuel (regular grade) is recommended for Prius. Higher octane may cause engine problems.

If you wish to experiment with midrange or premium I suggest that you buy just a couple of gallons so that you can easily reverse the experiment (by filling the rest of the tank with regular) if you need to.

 

Patrick is right, a partial tank of higher octane fuel for experimental use makes sense.

I had the clunks Thursday after using the block heater. A 'thin' oil hypothesis also makes sense.

Bob Wilson

 

Mine does it too. My guess is valve train noise. Possibly the chain or a sticky lifter. viscous oil can make the valve train clack a bit when cold. Happens on many cars. Nothing to worry about.

Bob's thin oil idea sounds like the most likely though. The oil on the chain and lifters dampens noise. Although there is a thin layer still present when you start a car, it takes a couple of seconds for the oil to soak everything. Good, fresh oil will be better at protecting your engine during those moments.

Our 1959 Meteor has sticky lifters that do this sometimes when cold from gummed up valve guides. I took off the valve cover to watch. A few squirts of WD40 on the stems got them moving almost instantly. Most modern engines don't have the sticky lifter/valve problem anymore.

 

There are no hydraulic lifters in a Prius. My Prius engine is a little noisy when cold but fine once warm so I'm not too concerned. One day I'll check the valve clearances.

 

yes i would agree with all above. I am almost certain is valve clearance noise. Mine does it same as everyone else. Lasts maybe 2-6 seconds on initial startup and then gone. Has anyone on here ever set the lash? I looked it up through the mainenance manuals and looks like you have to have the correct shim buckets. Its not a easy service to have done and it would probably cost quite a bit to have done. Each bucket needs to be checked/ measured and replacements depend on clearances for each bucket on intake and exhaust. I have been curious if anyone had it done at dealer and price?

 

Ignition timing is retarded upon cold startup for several seconds. The purpose of this is to help heat up the catalytic converter. Maybe this is causing the engine noise reported in this thread.

I removed the valve cover on my 2001 at ~60K miles and found that out of 16 valves, 4 had slightly more clearance than spec. However it looked like too much trouble to remove the camshafts in order to access the buckets, so I contented myself by replacing the PCV valve and reinstalling the valve cover.