My coolant cap is on the way out, it is rated at 0.9bar, just wondering what is the difference with a 0.9bar one or the sti 1.3bar

 

0.4 bar , basically it is the pressure rating of the cap. it wont pass any coolant into the expansion tank until the pressure in the system reaches that pressure.

 

I personally would stick to the factory fitted 0.9 bar pressure cap….

The 1.3 bar cap is meant for use in motorsport & would allow for higher coolant temps to be reached without running the risk of the coolant boiling and/or being forced out of the system.

I wouldn't really recommend them for use on a road car (especially older ones) as it increases the load on the cooling system components to almost 1.5 times the norm, which in turn will lead to an increased risk of the hoses or radiator failing, coupled with the fact that the factory fit a 0.9 for a reason and there would be no benifit by running a 1.3.

 

Modified.

 

Ta

 

go for a 1.1 bar one if you really must upgrade. thats what the 97- cars run.

 

That's not particularly helpful advice. On an old car with fibre HG's, raising the coolant pressure without good reason in this manner is unnecessarily tempting fate. One of the reasons the later cars have a higher pressure cooling system is because they have MLS head gaskets instead of the fibre ones.

 

I upgraded to a 1.3 with the forge header tank on MY95 STi. BUT I also have a larger ally rad, samcos and Zero Sports Thermostat. Just get a new OEM one, they're pretty cheap !

 

i run a 0.9 cap and have a forged engine build im wondering if i should swap to a 1.1 bar one as my header tank wil never stay full it will alsway stay an inch or so from the top ive always put this down to wher eits runnign almost 400bhp the temp of the water will be increased so it get rids of what it does not need and find its level

 

Doesn't the Sti come with a 1.3 bar cap?

PeteS

 

Afraid not no, the factory fitted the same cap as the one used on uk cars.

 

stick to the original rating for a standard engine, if want to improve the cooling system, then change an uprated thermostat ( which open at lower temp).