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Roker

Plastic Cover Underneath

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I was driving along yesterday and I heard clunk and then a heavy scraping sound. The air pressure in the engine compartment at a 100 km/hr was sufficient to blow the plastic cover under the engine out and it doubled back under the car scraping on the ground. This is the front cover that is attached to front bumper/skirt.

The problem was due the fact that during the last service they had not replaced all of the fixing bolts and I also scraped it on a high curb, The Avensis seems to ride on but grabs coming off the curb.

The hole were elongated so I made a couple of rectangular washer to fasten it up, one of the bolt holes under the engine area did not seem to have a thread, so I tapped out a larger bolt size.

I wonder are these plastic guards necessary? Will it alter the air flow if they are removed? It certainly makes maintenance more difficult if you do not have ramps or a pit, it will keep a lot of rain water out of the engine area but older cars did not have this.

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do not remove the cover as it helps airflow around engine to help cooling

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do not remove the cover as it helps airflow around engine to help cooling

Thanks davegooner7 for your reply, but this does not make sense, The radiator cools the engine, the plastic panels will direct the hot air from the radiator around the engine. I would have thought that the panels may be to prevent air resonating or to keep water from aplashing into the engine bay effecting plugs and sensors etc.

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do not remove the cover as it helps airflow around engine to help cooling

Thanks davegooner7 for your reply, but this does not make sense, The radiator cools the engine, the plastic panels will direct the hot air from the radiator around the engine. I would have thought that the panels may be to prevent air resonating or to keep water from aplashing into the engine bay effecting plugs and sensors etc.

The main reason for the lower cover is sound insulation- it stops the engine noise bouncing off the road surface back up to the cabin floor

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It's there for various reasons.

It protects the lower parts of the engine and creates an aerodynamic, flat, underbody which is supposed to produce less drag, less turbulence, less noise and better fuel economy.

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This seems to be a common enough problem to cause concern. My plastic undertray suffered a similar collapse on my way home from buying the car (a 55 plate D4D 2.2 diesel Spirit). I took it back to the dealer who refitted it. Two weeks later and the same thing happened again. The car came with a full service history and it seems that the undertray was replaced two years ago (the repair was described as damage to the undertray). Prior to my acquiring it, the car was a fleet lease vehicle and was professionally serviced, so it hasn'nt been bodged by an amateur mechanic. There is another thread on this forum, describing a similar problem which advises that a new plastic undertray costs around £200 - not cheap for what it is.

I put the car up on a hoist so that I could see the problem for myself. The undertray is secured with a mottley collection of bolts, plastic buttons and self tapping screws. The problem appears to me that the washers under the five self tapping screws that support the front of the undertray are only a little larger than the holes in the plastic. The plastic is thin and if it cracks along the mounting holes the undertray can be blown out from under the front apron and it then folds itself under the engine. From the look of the front apron, it is evident that this area is highly susceptible to damage from speed bumps which may be the initial cause of problems with the undertray.

My solution was to get a piece of 1mm alloy sheet. I used this to cut large support washers, shaped to fit into the recesses moulded into the plastic of the undertray to fit under each of the five self tapping screws. This gives the front of the undertray far more support and should ensure that this problem does not recur.

If I were an Avensis owner who has never suffered this problem, I think that I would be sufficently concerned that I would remove the original washers under the five front self tapping screws and replace them with larger diameter items for a bit of peace of mind. A cheap and easy fix that may save hundreds of pounds in the future!

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This seems to be a common enough problem to cause concern. My plastic undertray suffered a similar collapse on my way home from buying the car (a 55 plate D4D 2.2 diesel Spirit). I took it back to the dealer who refitted it. Two weeks later and the same thing happened again. The car came with a full service history and it seems that the undertray was replaced two years ago (the repair was described as damage to the undertray). Prior to my acquiring it, the car was a fleet lease vehicle and was professionally serviced, so it hasn'nt been bodged by an amateur mechanic. There is another thread on this forum, describing a similar problem which advises that a new plastic undertray costs around £200 - not cheap for what it is.

I put the car up on a hoist so that I could see the problem for myself. The undertray is secured with a mottley collection of bolts, plastic buttons and self tapping screws. The problem appears to me that the washers under the five self tapping screws that support the front of the undertray are only a little larger than the holes in the plastic. The plastic is thin and if it cracks along the mounting holes the undertray can be blown out from under the front apron and it then folds itself under the engine. From the look of the front apron, it is evident that this area is highly susceptible to damage from speed bumps which may be the initial cause of problems with the undertray.

My solution was to get a piece of 1mm alloy sheet. I used this to cut large support washers, shaped to fit into the recesses moulded into the plastic of the undertray to fit under each of the five self tapping screws. This gives the front of the undertray far more support and should ensure that this problem does not recur.

If I were an Avensis owner who has never suffered this problem, I think that I would be sufficently concerned that I would remove the original washers under the five front self tapping screws and replace them with larger diameter items for a bit of peace of mind. A cheap and easy fix that may save hundreds of pounds in the future!

It sounds a good fix, and is certainly a week point, not good enough for a car with only 45,000 mile up, even if it was partly my fault, it seem to be lower than other cars and catches the curbs, and is capable of riding on but grabs when reversing off.

.

I actual had two pieces of steel about 25mm by 75 mm long which I used to secure the under tray at the front. My car has a full Toyota service history but it looks like some of the other screws were missing. I notice that there are two machine bolt holding the rear part of the front tray, and although they screwed out, one had no mating thread in to the chassis. (Is this correct.) I am in the process of tapping this with M10 taps that I have and putting in an M10 bolt.

The whole thing needs some thought from Toyota designers.

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