Specifically it is the potassium 2-ethylhaxanoate (E-2A) used as part of OAT additive pack that eats silicone. There are a few OAT coolants appearing on the market that don�t contain E-2A and have added silicates (like old style blue IAT coolant), but almost all OAT coolant currently contains E-2A. The factory issue Yamalube/Motul Motocool is an E-2A based coolant and isn�t compatible with silicone based gaskets, sealants and hoses. Fortunately all the OE gaskets and hoses on the XT motor are silicone-free and OAT safe.

Incidentally OAT-grade silicone hoses are made from a more complex fluorosilicone elastomer, are harder to get hold of and are a lot more expensive.

Blissfully unaware of the OAT/silicone incompatibility, last year I rebuilt a Land Rover V8 engine refitting the valley gasket (waterways), water pump and inlet manifold using RTV silicone sealant. I thought it would be a smart move to refill with long life OAT coolant (rather than the Bluecol IAT I�d always used) � only it wasn�t a smart move! Three weeks having first run it coolant started weeping out of every joint. On inspection, the RTV sealant had gone soft and lost all structural integrity. After doing a bit of research, I remade all the joints again (with the same stuff), flush the cooling system and refilled with IAT coolant. Result � no leaks. Turns out I was lucky getting shot of the OAT coolant after just three weeks because the vast majority of all the gaskets used on pre-2006 Land Rovers are silicone based and would have gone the same way as the RTV over time. Interestingly the Blue Hylomar I�d used to help the thermostat gasket seat was unaffected after three weeks but that�s not to say it wasn�t on its way though, given more time � Hylomar seems to be a bit more resistant. Morals: (1) Stick to the coolant type recommended by the manufacturer; (2) Don�t mix OAT coolants (contains E-2A) and silicone compounds.

There is loads of stuff on the web about OAT and silicone, just Google it. In the US there have been numerous lawsuits involving Cummins, Chrysler, GM and Ford over gasket failures subsequent to their blanket switch to OAT based coolants.

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