08 Prius tapping noise increases after warming up

Hi folks - I have an 08 prius with 136K miles on it. My wife also has an 08 with 165K on it. My engine has always been slightly more noisy than hers. Recently mine seems to have escalated in the noise level. When I start driving the noise is more refined and blends more with the overall engine and exhaust sounds. But as it warms up instead of quieting down it gets louder and then levels off and stays at that level until it is turned off. Also, as it begins to warm up the sound source is still the same but the noise begins to have more of an edge on it. It is most noticeable when accelerating between 0-30 mph and when climbing hills. When not accelerating or on highways it is not very noticeable at all. I have tried higher octane gas which didn't make any noticeable difference. I have not replaced spark plugs but it's probably time.

I had a leak in my water pump the past winter which allowed some coolant to escape. I didn't notice the leak and I am in the habit of checking the garage floor for leaks. I did experience some sloshing noises which I ignored for longer than I should have. I added a little less than 1/2 gallon of coolant and ran it in inspection mode until the sloshing noise was gone, I have since dilligently monitored the levels for over 3 months now without needing to add any coolant. The water pump has seemed to heal/sealed itself.

I suppose one of my thoughts about why the sound increases after the engine warms up is that maybe the engine is not properly cooling. I did not do any bleeding to the coolant loop because I am only now realizing from reading the forum that there is an easily accessible valve and I also figured that the absence of any sloshing noise was sign that the coolant loop was good. I am wondering if perhaps there is still air present or partially blocking the flow of coolant ? I have not seen any CEL or warnings. Would higher than normal engine temp cause pre-ignition / ping.

Could some of the increased noise be coming from the water pump. I doubt a bad water pump can make a pinging noise but wouldn't the sound it produced repeat faster as the car accelerates. I do notice slight noise localized to the pump area when listening in inspection mode. There is also pinging coming from top of engine but not more than on my wife's car.

The other points worth mentioning are that my car was in an accident in 2012. The front clip of the car was damaged requiring replacement throttle body and condenser. That may or may not be relevant. Also, I noticed 2 years later that something didn't look right under the hood. When I looked at my wife's car I realized that that black plastic cover that connects via the front radiator support was missing. Thats the cover you'd have to remove to get to the radiator fill. They auto body shop said that it was not them and another shop or dealer must have failed to put it on. I'm not sure what purpose it serves but I didn't give it much thought until since this noise began.

One last thought- if there is anything easy to pull off my wife's car that would help troubleshoot this let me know. You might have some ideas that might not cost anything to try since I do have access to another 08 prius.

Thanks in advance for any feedback.

 

Good question based on the fact that I'm still running the same water pump although it did seep out coolant in the past. Seemingly a while back both our cars started using oil more than they had prior to hitting 100k so I've been keeping a closer eye on them. Before this realization, I did have one change where the oil was possibly down 1.5 quarts in my car. It was kind of a shocker when they had not been losing any oil prior. I don't believe this would have caused any damage that is only now showing up however.

 

Thank you for your response. So I take it that your prius does not see any improvement on premium gas ?

 

Understood and thank you ! Would I be correct in assuming that my hybrid battery is in decent shape if SOC consistently stays 3/4 to completely charged and my mileage is mostly showing 48-52 on my typical trips which usually are 15-20 mph of mixed driving conditions ?

Also, no one has spoken to my conjecture about higher than normal engine temp since coolant replacement and water pump leak or aging spark plugs ?

I believe I read somewhere that a hot engine is conducive to premature detonation ? I think I have the coolant situation stable and check it frequently. I'm not sure this is typically what one would expect but although the level in the coolant reservoir tank fluctuates which is normal when I open up the radiator filler cap the coolant level is always about a 1/4 inch from the top of the tube. Unlike the reservoir level ... I never see it's level change. I find that to be a bit odd. Maybe air blockage below it somewhere ? Do you think there is any point in opening the radiator bleed valve to allow any trapped air to escape.

I plan to order a mini vci device to scan for codes and hopefully find something that can be going wrong that can be remedied. With that I should be able to get a read on the engine temperature. Anyway, the ones that are available on amazon are inexpensive and have a few laptops I'm not using. The software is pretty powerful. Just need to be careful not to inadvertently upload any mods to the car with it.

I'm not ready to surrender to the probability that I've damaged my engine from one low oil event which didn't trigger a warning. I will probably go ahead and put in some new Denso spark plugs and change the PCV valve in the next week or 2. Can't hurt and should be done. I'm also not ruling out any contributing noise coming from pulley and water pump but will start at the top of the engine with things I can easily do myself first.