Underside Trim Damage

Interior and Exterior bodywork Faults and Fixes
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BRC
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Re: Underside Trim Damage

Post by BRC » Thu Jan 17, 2019 7:26 pm

I'm still confused Paul, why would the diesel fuel be hot in the first place unless there is a mechanism for it to be heated before it reaches the engine. The only thing I can think of is that re-circulating fuel on a flow and return basis can create heat from the pump especially when the pump is bypassing or dead ending but surely not be enough to warrent a heat exchanger to cool it.
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ChrisGB
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Re: Underside Trim Damage

Post by ChrisGB » Thu Jan 17, 2019 7:50 pm

You'd be surprised at how hot diesel fuel gets when it's being pumped around a common rail system. Even on the old VAG PD engines, the diesel in the tank could be visibly fuming when refueling.
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BRC
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Re: Underside Trim Damage

Post by BRC » Thu Jan 17, 2019 8:08 pm

Many thanks Chris, making more sense now. Guess the initial concern about putting a cooler in such a vulnerable location is still just that. I should have thought most cars at sometime or another are going to grind their undersides but perhaps there simply isn't enough room in the engine bay to house the cooler. Certainly looks pretty crammed in when you lift the bonnet. Ah well fore warned is fore armed.
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Re: Underside Trim Damage

Post by PaulC » Thu Jan 17, 2019 9:02 pm

The extremely high pressure used during injection generates a lot of heat, here's a long read if you fancy it: http://forums.tdiclub.com/showthread.php?t=20401

The location may seem daft, however, there's not really anywhere else they can put it - the optimal temperature for diesel is around 45C (which helps them keep the emissions so low), however, the engine bay is often hotter than this. Even with the current position, people experience issues with "misting" when refuelling due to the heat, so it could potentially be even worse if the cooler was in the engine bay.

If you think about it, most cars run the brake pipes under the floor pan with no problems, so I assume Jaguar took a similar calculated risk with their placement :-)

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BRC
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Re: Underside Trim Damage

Post by BRC » Fri Jan 18, 2019 6:54 am

Cheers Paul and I'll certainly have a read of the article. As you say brake pipes are also run underside and when you think about it much else besides. Timely warning to treat speed humps with a bit more reverence. :roll:
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PhilB
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Re: Underside Trim Damage

Post by PhilB » Fri Jan 18, 2019 7:14 am

A lot of people straddle speed bumps (the square ones) to avoid the bump but this in itself is potentially dangerous as the hump can cause damage to the inner sidewalls which you won't see or be aware of.
The advice from many sources including "Honest John" is to go over slowly using one set of wheels.
Domfow's damage was caused by road debris (Please correct me if I'm wrong) so people shouldn't be too worried and I've never encountered a speed hump that has scraped the underside.
If they do then they aren't to spec.
The plastic undertray on the XE gives a good deal of protection in normal circumstances and as far as I'm aware brake pipes are made of galvanized or stainless steel which is far stronger stuff than the aluminium fuel cooler mentioned here so no cause for people to worry or get paranoid.
:D
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BRC
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Re: Underside Trim Damage

Post by BRC » Fri Jan 18, 2019 7:32 am

You're absolutely right Phil and in practice I'm thinking of 2 speed humps I am sometimes obliged to "engage" with, both okay on the approach side but severly dipped on the exit. This as a result of a neaby local company driving their very heavy and fully laden dump trucks along that road. Been mentioned many times to our beloved Surrey County Council and met with their usual indifference!
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Re: Underside Trim Damage

Post by ant_in_wales » Fri Jan 18, 2019 8:30 am

Interesting about Good Speed bump strategy!
I'll have to change my way of doing this, plus parking further from my in-laws risky drive.
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Re: Underside Trim Damage

Post by PaulC » Fri Jan 18, 2019 9:45 am

I believe speed cushions were originally designed to be 2 traffic calming measures in one. Firstly they're a speed bump, but secondly they act as a chicane as traffic in both directions was supposed to use the middle cushion (or the centre of the road if there isn't a middle one) - that's why they're marked in the way that they are, you're supposed to hit the arrows with your wheels:

0bd323af0c8e9511c9f02cd3fb9e3295.jpg

The reason for cushions rather than a full speed bump was for the emergency services to be able to pass with a wheel either side en-route to an emergency (or an ambulance with a patient in the back).

Like most, I go over just the one, but I'm always wary of ones I've not encountered before as although there are specifications they're supposed to meet, they don't always. There's a road near me with 4 along the length, 1 of them feels "normal", 1 of them is so small you can fly over it without any wheel touching it, 1 is quite wide so you hit it no matter what, and the last one seems to be taller than the rest as the top of it is full of scrapes from the underside of vehicles.
Cambridgeshire are starting to introduce 1.7m wide cushions on their roads as they slow down both cars and HGV's, so if you see one and think you can go over it at 30Mph, think again as if it's one of the wide ones you're in for a bit of a shock.

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PhilB
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Re: Underside Trim Damage

Post by PhilB » Fri Jan 18, 2019 10:57 am

I think those arrows are also luminous to make the humps more visible in unlit areas.
:D

One thing about humps is the old pedestrian protection system or the pop up bonnet which fires if you hit someone to reduce injury.
Bloke on the F-Type forums had his fire just going over a full width ramp you sometimes see.
According to the manual it should only work between 16 and 31 mph and on a frontal impact but he says he wasn't going over 15 mph and didn't hit anything.
Either way he had a terrible row with JLR trying to prove it must have been a fault as the car apparently recorded an impact of over 80G.
According to a member over there who is also a doctor, over 80G would be fatal.

Just something to bear in mind before you bounce over those ramps as apparently the cost of fixing it after activation is 4 figures !
:shock:
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