Matt M replied:

Ian, do all the obvious things first, like ensure the engine is running at correct operating temp etc! If all is fine then I would look at insulating or upgrading the insulation under the body of the veh. To help remove some of the exhaust heat, get rid of the standard manifold and thermal tape the extractors before you fit. This would surely reduce some of the under body heat.

Goodluck

Matt.

Member - Peter replied:

Ian when I got my humvee it had no under body insulation or soundproofing at all so I started with a clean slate so to speak.
Firstly I painted the underneath with one of the generic underbody sound deadeners, they come in spray and brush on containers, the spray being good for hard to get at places. I would imagine that the L300 probably has some on it already.
Firstly make sure the underbody is clean and dry, degrease the whole thing with truck wash if it isn't too bad, degreaser if it is very dirty.
Then apply the deadener if required.
Then buy some firewall insulation from Trufit down in Dandenong (www.tru-fitcarpets.com.au they make the fitted car carpets and advertise in most of the mags). This stuff has a reflective foil like skin then a tough woolly stuff about 10mm thick, then a peel off sticky back which you stick under the floor, firewall etc. You can't tear it and it won't hold moisture and it makes a huge difference to the heat transmission. You can cut it with sharp scissors/industrial cutters etc
Then on the inside go down to Kmart or similar and get a couple of those cheap sleeping mats, they come in all colours and are about 10mm thick, cut and fit them to the floor under the existing mats using contact gel to stick them down. They also won't hold moisture.
If you still require more soundproofing/insulation you can get from the same place in Dandenong sheets of interior felt/bitumen/felt stuff which you can put on top of the mats but if you get too thick the mats won't fit real well.
I've done the cheap sleeping mat trick to several troopies over the years and it works well, Glue it down unser seats, the sides of footwells, firewall etc and just lay it loose under the footwell bits for cleaning and then put the original mats back over the top.
Peter

Eric Experience. replied:

Ian.
There are a couple of ways to solve this one is to get more air through your radiator, do you have any shade cloth over you radiator? if so remove it. the other thing is to make a heat sheild over the motor, I used .5mm stainless and riveted it to the body with 6mm spacers between to allow some air to pass between the heat shield and the body. Eric.