Thread: LT95 extended cooling sump

Originally Posted by JDNSW

I know it feels as if the heat is coming off the transmission, but I strongly suspect that most of the heat actually comes from the engine - the hot air from the engine is pretty much channelled alongside and over the gearbox by airflow blocker called a gearbox crossmember. Some air goes below it, but most of the hot air, preheated by the radiator, heated by the external surfaces of the head and block, and superheated by the exhaust manifold, is confined by the bonnet, inner mudguards, chassis, and sideways sump extension (especially on the left) to flow through the gap either side of the bell housing and between the gearbox and the floor/transmission tunnel.

If you think about it for a moment, of the energy from burning fuel, about 25% is converted to mechanical energy, of which only 1-2% is lost as heat in the gearbox. The remaining 75% remains as heat and is transferred by the cooling system to the air flowing past the gearbox, except for a relatively small proportion that is still retained in the exhaust.

This strongly suggests that improved gearbox cooling will not have a noticeable effect on the floor temperature! (It might help the gearbox though, as the 'cooling' airflow round the top and sides of the gearbox is probably above coolant temperature in hot weather)

As suggested, managing airflow is likely to give better results (or simply use thermal insulation).

John

After running an Engine Watchdog temp sensor on the back of my transfer case for a few months, my rough observation was this:
- 30deg day, highway driving, towing approx 1.5T
- it takes about an hour for the transfer case temp to reach a stable temp - in this case around 80deg.
- engine temp was stable at around 80deg 10mins after starting
- maximum transfer temp recorded around 90deg (extended winding uphill section), and engine temp slightly lower
- transmission tunnel temp definitely increased more in line with the transfer temp rather than engine temp, but as you suggest, it could well be a case of the engine heats the air, the whole area gets hot so the transfer cant shed as much heat and everything pushes up to a higher temp.

Personally, I'm going down the thermal insulation path - exhaust wrap, seatbox and trans tunnel insulation etc. Will be interesting to see if the exhaust wrap makes a difference to the transfer temp.
If one was available, it would also be very interesting to run a finned sump to see what (if any) difference it made to the transfer temp. If, as you're suggesting, the air around that whole area is already at a high temp, it may not.

Steve

I'd be hesitant to wrap the exhaust if you do any off road work. The trapped dirt and moisture will would increate the corrosion rate a fair amount. The best option if you have the space is heat shields. The exhaust wrap is generally used where space it tight, or a heat shield isn't practical. Also the main source of in cabin heat is usually hot air entering the cabin through open holes and gaps in the floor and firewall, although most counties would be quite well sealed.

The corvette guys talk about this a lot as the 70's vettes have a tight footwell with a large hot V8 and gearbox close by, and two exhausts running right under the floor.