Hood Vibration Observation

[thejuice]

I was tinkering around in the engine compartment. There's this plastic cover that extends from roughly the engine to the front of the engine compartment, hiding the top of the radiator. I couldn't find it in any of the parts diagrams (maybe it's the sight shield), but it's held in place with about 10 fasteners.

I removed that plastic cover and had it out for about a week. I noticed that driving down the highway I had a LOT of hood vibration, and when I returned the plastic cover the hood vibration stopped.

I know there's been a lot of discussion on hood vibration, and I wonder if one culprit isn't air getting blown into the engine compartment and rattling the hood from underneath. Thoughts?

 

[1engineer]

I was tinkering around in the engine compartment. There's this plastic cover that extends from roughly the engine to the front of the engine compartment, hiding the top of the radiator. I couldn't find it in any of the parts diagrams (maybe it's the sight shield), but it's held in place with about 10 fasteners.

I removed that plastic cover and had it out for about a week. I noticed that driving down the highway I had a LOT of hood vibration, and when I returned the plastic cover the hood vibration stopped.

I know there's been a lot of discussion on hood vibration, and I wonder if one culprit isn't air getting blown into the engine compartment and rattling the hood from underneath. Thoughts?

Jtraskell has this idea also. I don't know if he put it in a post or just in pm's to me though. It is entirely possible. I know we compared hood gap measurements on our 4Runners though. This is the gap between the grille front facia and the leading edge of the hood. I think mine had less gap and I explained that there are adjustable hood stops located on the inside of the front of the fenders that he could adjust. Problem is that adjustingthese also means the hood latch striker will probably need adjusting and you also have to look for level alignment from the hood to the top of the fenders.

 

[Jtraskell]

Thanks for opening the door 1engineer:biggrin2:. OP, your observations and conclusions are spot on. I have not posted my findings until now, since I was waiting for this issue to reappear.

As you know, hood flex has been talked about a lot over the years. I too had the concerns. Here is what I did quite by accident! But this stopped the hood flex completely. First, for completely other reasons (mostly aesthetic), I bought a AVS bug shield. After installation, I noticed the "gap" between the top of the front grill and the bottom of the front of the hood had been almost eliminated. (It looked better). But I also noticed that the hood flex had been greatly reduced!

I then bought a hood liner that normally comes standard with the limited model and installed it on my SR5. After that, absolutely no hood flex. Again, I purchased the hood liner for aesthetic reasons, but this was the additional benefit. Yea!

So I got to thinking as to the possible reasons why. I always noticed that some of our 4 runners have a large gap at the front hood area, others did not. Fit and Finish issue that I was surprised to see on a Toyota. (See posted photos of the various members vehicles). Now, with your observations OP, I think this clinches it. Too much air flow coming into the engine bay here it was not designed to come in, is at least one cause of the flex. Filling in the gap, (with my bug shield) and putting a little more strength or thickness to the hood itself (hood liner), solved the problem with mine.

If others here have hood flex concerns and you have a gap between the top of your grill and bottom of the front center of your hood, (say more then 1/2 inch, mine was over an inch I think) try this. Get a piece of foam pipe insulation. You know, the foam tube with a slice down one side.

Get a piece large enough to fill the gap of your hood. Get up to speed where you normally see the flex. (Make sure your on a smooth road) See if stopping the air flow from that gap doesn't help or maybe even stop the flex completely.

If so, you can adjust the hood as 1engineer suggests, or maybe there is a way to adjust the grill? Or fill the gap like I did. OR? Be safe.