Coolant expansion tank.

vij

I have been updating the cooling system on my 1991 851/996 to the same system as a S4. Now I was thinking about replacing the old expansion tank with a smaller one that I want to install just in front of the tank were the regulator normally sits. I have seen the 916 tanks and they look like they might be in a good size. Does any one have any experience if fitting one of them. I was thinking about this one.

Jocke.........

Hatman

They go bad quite often, particularly with track use. We always kept a couple of spares on hand when I was racing the 748/916/996/998 bikes. They're pressurized, so when they do leak, it gets messy fast. A few folks have made aluminum replacements, and a lot of racebikes used an aluminum tank up front in the headlight area (don't know if that was a Corse part, aftermarket, or one-off).

If you buy one, you might check the cost of new vs. used -- here in the US they're only about $40 USD brand new.

vij

Hatman wroteThey go bad quite often, particularly with track use. We always kept a couple of spares on hand when I was racing the 748/916/996/998 bikes. They're pressurized, so when they do leak, it gets messy fast. A few folks have made aluminum replacements, and a lot of racebikes used an aluminum tank up front in the headlight area (don't know if that was a Corse part, aftermarket, or one-off). If you buy one, you might check the cost of new vs. used -- here in the US they're only about $40 USD brand new.

Hmmm. Why are they pressurized? I am a bit lost here. On 851 and also on S4 it is just an expantion tank that ventilated to the outside air.

Jocke........

Edit

Okay. After having a look at the 996 part catalog I realized that on 916 series bikes the expansion tank is a part of the radiator presurized circuit and that the overpressure cap is on the expansion tank, not on the radiator as on S4 and 851. I was thinking about using the 916 expansion tank in the same way as the original (unpressurized) and just vent it to the air. How does the cap look? Is it possible to install a 851 cap or is it different size on it?

Jocke.........

Mr.R

Hi Jocke,

On my 851/916cc bike I just zip tied a plastic bottle* to the RH side of the radiator, there's a 5mm hole in the cap that vents to atmosphere it works perfectly and has done for thousands of miles/quite a few years now.
... and it weighs 2 5ths of F'ck all! 😎
But you can smell hot coolant after a fast thrash.

*The plastic bottle is actually a genuine HRC part for a race RC 30

Steve R

vij

Mr.R wroteHi Jocke, *The plastic bottle is actually a genuine HRC part for a race RC 30 Steve R

WOW. I like that. Genuine race parts are always the best. 😄

Jocke...........