Expansion tank cap pressure question

Hi guys,
Just a quicky...what's the correct pressure on a coolant expansion cap on a 2005 4.4 v8 petrol l322...I have 200psi...
Is that correct ?
Thanks
Ian

200psi i would think nearer 20psi or less

The cap on my v8 and commonly used on other vehicles, is stamped with the number 140. That's 140 kPa, or approx 20psi. A normal, healthy petrol engine will be well under 10psi when it's at operating temperature
Don't ask how i know!!

Hi, mine says 200, cant remember what it is ie psi or whatever ...guess its 200KPa, reason for asking was the water pump was leaking I've got a new one and a new thermostat and I watched a YouTube video and the guys expansion cap was rated at 140...and I thought hello mines rated at 200...hence the ask...ok il order up a cap from the dealers as soo as they are open

Thanks guys...your the best

More than Likely 200kpa

It is certainly not 200 PSI that is for certain. Normal max coolant leak off pressure is in the 15 to 20 PSI range depending on system. Normal running pressure will be lower than that.

200kpa for bmw petrols
140kpa for bmw diesels.

stustrong said:

200kpa for bmw petrols
140kpa for bmw diesels.

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200? really? thats nearly 30psi! thats mental
my bmw 3 series has a 140 cap

kermit_rr said:

200? really? thats nearly 30psi! thats mental
my bmw 3 series has a 140 cap

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Yeah that's correct.
Alot of drifty folk put the 140 caps on the petrols in a hope itl stop the expansion tank exploding.
It does but then just leaves less room for error if it does run slightly hot.
All 4 of my petrol 3 series have the 200 cap.
Both diesels have the 140.

stustrong said:

Yeah that's correct.
Alot of drifty folk put the 140 caps on the petrols in a hope itl stop the expansion tank exploding.
It does but then just leaves less room for error if it does run slightly hot.
All 4 of my petrol 3 series have the 200 cap.
Both diesels have the 140.

Click to expand...

what is the normal operating temp of your cars? what temp does the thermostat open at?

88° stats opening stats 94ish running temps.
All inline 6s
Upto 105° is acceptable.

Diesels seem to hover about the 90 mark.

pretty standard then. i've seen 107c on my beemer
at 20psi/140kpa, boiling point is raised to over 135c!
I dont think a 200kpa cap would be helpful to anyone, i wouldn't want my car running at 120c, nevermind 140c

It's not the operating pressure it's the max pressure it will vent at.
In a fail of an electric fan situation I'd rather my system held more pressure then vent early and spew its coolant.
Hotspots in the head ect will exceed the recorded temp.
There must be good reason they used a higher pressure on the petrols. 1990 to 2005 with very crap and brittle coolant systems.

A normal running motor with no deeper issues it will not matter with a 140 or 200 cap.

But with the 140 cap it may just cover up smaller issues till it's too late and suddenly boil up.

you're right.. 2 ways of looking at the same issue i guess. though i'd hope a driver would notice dash warnings before an engine killed itself

You would hope so quick check of the gauges doesn't take much. BMW ecus wont move the needle from center point till it's over 1115°. The hex code in the Siemens ecus can be changed to buffer the gauge diffrent. Eg ones I skid iv got them changed from 3/4 being 120 to 105° old 125° would be top of the red iv mine set to 115°

To say il spend 2.5 hours towing a car down to sit at 5-6k with low airflow through the rad for 5hours then tow home. I'd not want to end my day early due to an overheat and I still keep the 200 caps with no issues.

M62 is set to run at 105° unless being loaded hard when the ECU opens the stat further and can drop down to low 90's....over 120° and the warning bells go off.

more chance of a sudden coolant loss with a too high a pressure cap