Coolant and Fuel Hoses - pitfalls and solutions
Coolant hoses
There are several vendors who offer ‘Kevlar reinforced’ replacement coolant hoses. In our experience these are of poor quality, and far from offering long life are in fact much shorter-lived than the original manufacturer’s hose.
We experimented with these from a well-known Jaguar parts specialist in 2008 and were horrified to experience a severe hose-burst on a motorway necessitating an expensive recovery of the client’s car (an XJ12 Series 3). We narrowly averted similar problems on a number of other cars when we found the bends in the hoses were badly formed resulting in the hoses abrading through against sharp bits of engine. Anyone who has worked on the V12’s hoses will know that space is at a premium in the engine bay, and the position taken by each hose is critical to ensure it does not hit anything.
On investigating the damaged hoses and others in stock we found that the bends were very inaccurate, the reinforcement fibres were either not really Kevlar or were just too weak – or maybe not bonded well inside the rubber so that they could work loose.
We can’t say that all Kevlar-reinforced hoses are substandard, but KWE would never ever take the risk again. A burst on any hose on a V12 spells almost instant curtains for the engine.
The best hoses are the cotton-reinforced oem hoses available only from genuine Jaguar parts counters. However, we have experienced some faults even on oem hoses used on the 4 litre 6 cylinder engines, where at the reinforced unions on multi-branch hoses the joins are not waterproof and so they leak. We have worked with Jaguar to correct this and we note that later hoses all have an inspection mark.
It’s important to use the right sort of hose clip too. The relatively sharp-edged wide band ‘Jubilee’ clip is not ideal as the edges can bite into the rubber. We prefer to use Norma clips (from Wurth for example) which are thin and have a partly rolled edge.
Always use rubber grease (red) on the inside of the hose at the union so it slides on easily, and on the inside of the clip, and lubricate the clip’s worm drive with a rubber-friendly grease (not mineral oil) so that the clamping force is applied evenly around the hose. On the metal hose unions make sure the union is quite clear of sediment build-up – usually to be found on the most inaccessible side! – otherwise it will leak here. We find nylon scourer material such as Scotch Brite very good. You may also find a build-up of hardened coolant sealant which can be tough to remove. (Watch out for our forthcoming article on the horrors of using such sealants. In the meantime, don’t)!
KWE offers a special package for changing all the coolant hoses, drive belts and ignition leads, including a chemical flush of the cooling and oil systems and a full 15,000 mile service (upgradeable to 30,000 miles) for the whole car.
Fuel hoses
There are various grades of fuel hose and it is very important especially on pre-1991 engines to use the correct type. The issues involved are temperature, pressure and fuel additives.
Outside the engine bay fuel hose need only be fuel-proof (but see below) and able to withstand at least 8 bar (112psi). But in the engine bay it must also be able to withstand around 100degC, and, most critically, the fuel injector stub hoses on the pre-1991 V12 injectors must be able to withstand at least 120degC. These hoses were well-known to burst (until Jaguar got the formulation correct) spraying high pressure petrol all over the (sparking) distributor. Inevitably the XJS gained a reputation for catching fire.
With all these injector hoses being at least 24 years old now (at 2015) they will be stiff and cracking with age. Some garages will fit ordinary fuel injection hose but this is very likely to burst – we have experienced this first-hand. It is thus vitally important to replace the injector hoses, and to use only the correct hose material.
A further complication is that petrol now contains a significant percentage of bio-ethanol (up to 15% and likely to rise) which attacks certain types of rubber. Accordingly, KWE only uses ethanol-resistant high temperature, high pressure hose which is very expensive and quite hard to find. It is also vital that the original Jaguar hose clamping method with precision-fit ferrules is retained – conventional hose clips are not suitable as they leak after the pipe hardens.
KWE offers a complete fuel injector rail reconditioning service which includes a re-plated rail, reconditioned injectors and new hoses, all pressure-tested.
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