I think I finally found the reason C43's seem to run hotter compared to other similar cars (W210 E55 and W208 CLK55).

The C43 has two coolant bypass's running of the back of the heads rather than the usual one only. The normal bypass is used for the heater. In the C43's the second one is used for the transmission cooler. Most engines need one bypass line to stop hot spots and uneven temperatures, nothing unusual here.

I had a theory that having two bypass hoses instead of one was making it even easier for coolant to go "round in circles" rather than go through the radiator. I initially had an idea of running the return from the transmission cooler to the inlet side of the radiator so it could be cooled. The problem was potential overcooling under cruise conditions or a potential reducing of transmission cooling if I put a inline thermostat in the coolant hose (VW's with DSG had the perfect thermostat).

After a embarrassingly long time staring at problem (literally) I came up with the idea of using as much of the factory setup and simplifying the problem as much as I could. The result was using a normal lower radiator hose rather than the C43 specific hose, rerouting the heater return line to a t-piece on the inlet side of the transmission cooler. The return from the transmission cooler would then be connected to the inlet of the water pump (where the heater return line would normally be). This setup required only 1 inline joiner, 1 t-piece, 1ft of 1/2 heater hose and some braiding to put over the existing heater return hose incase of chafing.

The idea is that there may be 2x 1/2" hoses coming in but if there is only 1x 1/2" hose going back to the engine like any other M113 then the flow should be reduced. There is no additional thermostat and the coolant flow to the transmission cooler hasn't been reduced, any reduction in flow to the heater would be counteracted by the heater valve opening more and boosted by the heater booster pump anyway.

The end result that I have tested in 37C/100F+ temps is a more stable engine temp, slower temp rise when stationary in traffic, faster temp drop once moving again. There has been no change to gearbox temps, the heater seems to work fine (limited cold temp testing so far). I wish I had done this before I upgraded the radiator, I may not have needed to

For those in hot climates this is a cheap and easy mod that might work for you!

 

Great write-up and recommendation. I may go down this way as we also get hot temps in summer, together with mountain drive conditions which always increase engine temps.

 

can you tell us what parts we need?
and the partsnumber for extra hoses
and a step by step instruction?

thanks

 

All you need to perform this modification is a new lower radiator hose (A202 501 5082), a few quality hose clamps, about 3ft of heater hose (1/2"), a 1/2" hose joiner and a 1/2" t-joiner.

The hose from the aux pump to water pump needs to be cut. The water pump end is reused as pictured, the aux pump end is now rerouted to the inlet side of the trans cooler. It's a bit hard to take a picture that shows all the connections so I drew a basic coolant circuit diagram to help show the changes.
See pics for more details.

It's a little tight with the front bumper still installed but it can be done.
It won't suddenly make it run cold but it does help get the most out of the cooling system we have.

 

This is quite interesting. I haven't had too many issues with heat & don't have any canyons to take, but still might take this on if I'm bored this winter. Thanks for the write-up :thumbsup:

 

moderators can put this thread in the stickies DYI archive, so we don't lose the tutorial pictures

 

Has anyone done this with good results? I like to try it since I need the bottom hose replaced.

 

Interesting.

I'm in FL and never had cooling issues. Nice to know though!

 

It's funny that since replacing my radiator 2 years ago, the engine runs way cooler than before, in all type of driving conditions. Was the older rad becoming clogged inside, or perhaps the junk flying through the fins impaired air flow? In all cases the new radiator improved things greatly. The thermostat works perfectly, heating the engine and cabin quickly after start-up. So don't think the cooler running temperature comes from that part.