Can i start and run car with radiator cap off ?

[Thraxeh]

I'm calibrating my Temp gauge, and i need to stick a thermometer into the water to get the most accurate reading possible. Is it fine to run the engine while the radiator cap is off ? or will i get coolant spilled everywhere ?

[Mr_Toyota]

Ive started and ran my hilux with no cap for about 2mins ideling..

so probably, but then again i dont know if the hilux was at its running temp.

[Ghetto-AW11]

When the coolant gets hot, it will expand ie... flow out the radiator cap...

[BigWorm]

Yeah that's fine, it'll take quite a while to get it up to operating temp with it just idling though, both my cars usually take around 10 mins at least, if you're prepared to have to give things a bit of a rinse with plain water afterwards it's no big drama.

[clubagreenie]

When the coolant gets hot, it will expand ie... flow out the radiator cap...

o'rly?

i thnk youll find its more to do with the fact that the water spot boils and the generated gas forces water out

in answer to the question - its perfectly fine to start, and run, and rive the car withou a rad cap - however the collant will boil at a lower temp, and will eventually overflow due to this boiling - so carry a bottle of fresh water to top up the system as you go along....

[Ghetto-AW11]

so it doesnt expand at all?

[bionikal]

lol, in my laser i had the cap off while running a few times.

but then again its got a radiator leak somewhere (assuming badly clamped hoses) and it dumps water whenever its under pressure.

engine wise i dont think it has any bad side effects, it didnt die or explode after doing it. i cant think of why it would..

worse case scenario is you get an some air bubles or some dirt flowing through.

- edit YES it does expand, but being water, it also evaporates you will probably get a little overflow.

[Screamn_Sleeka]

Takeing the cap off and running it is fine, thats one of the ways u check for a blown head gasket, bubbles and a lot of pressure.

[bionikal]

Takeing the cap off and running it is fine, thats one of the ways u check for a blown head gasket, bubbles and a lot of pressure.

i thaught it was white under the oil cap

[MRMOPARMAN]

if there is something wrong with your engine and it is overheating, then yes it would be boiling water blowing out of the radiator. otherwise its just natural expansion of the coolant that will flow out of the radiator.

just be careful that the expanding water doesnt hit a moving fan and splash up into your eyes or something.

[Starfire]

The water does expand a little, which is whtat the overflow bottle is for. The cap maintains pressure in the system which raises the boiling temperature.

Be careful if running your car without a radiator cap not to overheat it - it is quite easy to warp an alloy head.

[Screamn_Sleeka]

i thaught it was white under the oil cap

thats one of the ways

There are many ways to diagnose a BHG.

And Starfire is right, the over flow bottle will be the first place "expanded" water will go, not that it will happen under normal circumstances.

[Thraxeh]

what is the highest normal temp the car can run at ?

[ed]

so it doesnt expand at all?

The thermal coefficient of expansion of water is 0.00021 per 1° Celsius at 20° Celsius

you dont have a spare 80cc of volume in your cooling system?

the reason coolant spews is spontaneous boiling within the fluid (in a closed space) which gets forced out the open rad cap. thermal expansion is slow and boring, and nearly irrelevant to the 'safety' of running an engine with the cap off

[lojik]

Would it be difficult to have a container of just boiled water, drop sensor in and calibrate from that, rather than messing around with the radiator cap off?
just a suggestion...