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Old 03-10-2013, 09:13 AM
JimLev JimLev is offline
Officially Welcomed to the 'Fest
Location: Sundance Mesa, NM
Join Date: Dec 2003
Posts: 4,319
Mein Auto: 540/6, '16 Highlander XLE
Originally Posted by Dragan View Post
Has anyone actually had a pressure gauge hooked up to the cooling system in the following conditions:

Idling when cold

Idling at operating temperature

at 2500 rpm with fan blowing air through rad to simulate highway cruising

I'd be curious to see all the pressure readings under these conditions.
And another thing that hasn't been clarified, is the 2 bars of pressure gauge or atmospheric? I assume it's gauge since that's how we measure everything else (tires, fuel pressure, etc.).
Here ya go. This is on my 2000 540 (M62tu engine) with the 2 bar cap. I do have a 1.4 bar cap but didn't use it as the cap doesn't effect the pressure.

I did this last fall, so the outside air temps were not in the 90's, no AC either.
I'll do it again this summer and see if it changes much.
It was posted and graphed on the other message board.
I heated the engine up in my driveway with the electric fan off to allow the engine to heat up quicker.
When the KTMP reached 103C I took the car out for a spirited drive, the temp never rose above 105C.

KTMP Reading/PSI Reading
40C/1.5 PSI
45C/2 PSI
50C/2.25 PSI
55C/2.5 PSI
60C/3.0 PSI
65C/3.25 PSI
70C/3.5 PSI
75C/4.0 PSI
80C/5 PSI
85C/6 PSI
90C/6.5 PSI
95C/7.5 PSI
100C/9.0 PSI
105C/16.5 PSI

When I returned from my drive I released some pressure via the cap. It was then down around 5 PSI. I went out for another drive, when I returned it was still at 5 PSI.
I'm going to modify the t-stat heater circuit to drop the temp which will drop the pressure.


2000 540/6 Slightly tweeked...everywhere
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