I am looking for some input from anyone, but especially factory trained techs who might have picked up some information in the initial factory tech training on the X350.

What are the technical reasons for the large plastic undertray on the X350, the one that stretches from the bumper skidplate to the midpoint of the transmission (and covers the oil filter)? What if this tray was permanently left off? Any negative impact to anything? Or, put another way, did the factory give a technical explanation for this tray.

Thanks,

 

The technical explanation was increased aerodynamics and improved fuel economy. This is the reason given for all three of the undertrays.

 

Thanks Real Tech, I appreciate the answer. I wanted to make sure there were no temperature related issues or component cooling or heating issues. I might remove it on my X350 which is nothing more than a city car and daily driver. It doesn't get used much on the highway. I find myself doing more things with it where I am R/Ring this cover mre than I want to do.

BTW, isn't one of the three undertrays the cause for the safety recall - corroded brakelines? Moisture or snow accumulating under the tray?

Best,

 

The right side tray has an insulator pad at the rear which is mounted where it contacts the brake lines. The pad likes to hold water and road debris builds up here making the problem worse. We've probably checked at least 400 of these at the shop and they seem to be running about 50% requiring replacement of the brake lines. I am in the rust belt so southern or south western cars may have a lower replacement percentage.

 

My left and right undertrays are shot and the dealer quoted me $510 for the parts and labor. They claim that the parts alone cost more than $400. Should I call BS or are they in the right ballpark?

In addition, does anyone have the part numbers handy so that I may do some independent research to see if I can locate used covers.

Am I playing with fire if it takes me a couple of months to get these fixed?

I would greatly appreciate any recommendations or other insights....

 

These items should be showing up in scrap yards about now. That's the only source, short of the OEM, that might have them.

 

Ebay should have them.

 

Nevermind, just checked eBay, they don't have them.

 

What's wrong with them? A crack or hole is easily repaired with a fiberglass repair kit available at any auto parts store.

 

at $400 Ide leave em off, but they also protect the brake and gas lines from road debris like rock etc... the engine/trans under tray is fantastic and holding(hiding) leaks too
another benefit to the factory for reduced warranty comcerns. if you dont see drips on your floor from your car then it does leak now does it.............

 

I imagine that the fuel savings due to the undertray is negligible. From the looks of the things with their insulation pads they also dampen road noise on the aluminum chassis. The high tensile aluminum is bound to be worse for noise transfer than the old steel underpans. I can see no critical reason to keep them either. If I had a problem with one, I would dump it in the trash. If I didn't like the results, I would replace it when convenient. I have already had the problem of the side underpanel bolts corroding and turnign the captured studs on attempted removal so that I have had to cut them out and refasten elsewhere to get to the fuel filter. If I have to mess with one again it's gone.

 

I bet it has most to do with cooling air flow, keeping the engine bay cleaner, and protecting from debris in the road. Why do people insist on removing such an important item for the vehicle?

In the X350, doesn't the undertray (at least the front one under the radiator) also kind of hold the front bumper together?

 

I'd replace them if broken. Buy them from a Jag parts discounter and anyone can mount them. The aero is important especially at highway speeds.

 

When I bought my car the front tray was cracked. I removed it and repaired it with a fiberglass patch. No issues since. I also have one of the brass thread inserts that just rotates in the frame. Now I just use a plastic panel brad to hold it on. The kind that spreads when the center button is pushed in. It is reusable and works fine.

 

My vote is for high speed stability. I remember seeing a TV special on the early years of Jag racing/development. The Le Mons racing team was able to get quite a bit more speed out of the Jags by installing full belly pans. If I recall, they then had some heat problems to sort out.

Given how interrelated this all is (air flow, heat, stability, speed, etc.) and how much money is spent getting it all optimized, I would keep it as stock as possible.

 

yeah, I would put them on, its not a huge cost really.

 

Thanks all. In response to Lew's question, the driver's side undertray is torn and a large portion is hanging underneath the car. The right side has tears, but is in much better shape and still fully attached. From the back of the car, I can clearly see the white mesh (?) covering the bottom of the car near the driver's side exhaust, but it is not as visible on the other side.

At some point, I need to fix the driver's side and might as well take care of them both at the same time. I was hoping to save some cash, but could not find them on eBay. I also cannot locate the part numbers and the dealer writeup does not list them.

Thanks again for all the commentary. You guys are awesome!

 

Just saw the earlier post with the attachment showing the part numbers. Very cool.

 

$400.00 for both trays sounds right to me. Hell being a Jag tech myself I've seen part prices that are insane. I'm actually surprised they are not more then $510.00 parts and labor. Alot of time the bolts and nuts that hold those trays on strip or rust and wont come off. how bad are the trays. Those covers protect the fuel filter and lines on the left side, and the brake lines on the right side. They're pretty important.

 

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