Can i start and run car with radiator cap off ?

[Ghetto-AW11]

I never said it was dangerous, i said water would come out of the radaitor cap...

[ajh]

Thraxeh,

If you're the person I'm thinking of, you have an SV21 correct?? (I think I've replied to you re: temperature gauge)

I've run ours with the cap off plenty of times.

Mainly to bleed air out. When the thermostat opens, you'll see the coolant start to flow through the radiator instead of sitting there.

The level will rise slightly too and the coolant gets BLOODY HOT!!!

Oh and by the way, anytime now, the thermo fans will start so mind the fingers!!! I had a near miss........Also be careful when a little coolant runs out of the opening, it will run down and get drawn into the fans (if they are running) mind your eyes, as it will spray up and hit you in the face.

Cheers.

[Mos]

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

That coefficient of expansion applies only at 20°C. The coefficient increases at the temperature increases.
Overall expansion from freezing to boiling is about 4.3%, which is somewhat significant.

If a 1GZ-FE takes about 15L of coolant (and it does), the expansion to boiling would be over 0.6L, which is significant and will expand out into the overflow bottle.

That said, as everyone said, it's fine to run an engine without the rad cap, as long as you keep in mind the boiling temp is reduced. In a normally operating engine this should not be a problem for testing purposes.

Mos.

[thechuckster]

to calibrate a temp sensor/guage:
preparation
-get a cooking themometer (digital or old-style)
-fill up kettle and put onto boil
-fill up a metal jug of water and leave in the sun to warm up to ambient temps
-fill up a plastic container and put into the freezer to cool down
-obtain some human help to carry stuff around or read the dash guage
-remove the temp sensor from the head, leave connected and earth the case with another length of wire

measuring
-get helper in the car ready to turn the ignition on and look at the dash guage
-you get to read out the thermometer
-get freshly boiled jug from kitchen and dunk sensor and thermometer in it - take readings after 30 seconds
-get metal jug from sunny spot, dunk sensor and thermometer in it - take readings after 60 seconds
-get plastic jug from freezer, dunk sensor and thermometer in it and take readings after 60-90 seconds

you now have actual temp readings at approx 0, 25 and 100 degrees C relating to what your guage says...

note: don't use the hot water mentioned above to make coffee - tastes horrible. Also, don't dunk the sensor into the the hot water kettle - makes future cups of coffee taste strange.

[MRMOPARMAN]

most cars run in between 95-115 celcius. most jap cars run on the hotter side for efficiency. it really depends on the engine. i know the old clunker VN buick engines operate at 105!

[Thraxeh]

the gauge was off by around 7 degrees, it was 7 degrees too high... i worked out i needed a 27ohm resistor between the sender and gauge to get it down to an accurate level.

thanks for the replys, i gave the car a drive, parked, took off radiator cap and gave it a measure

[mrshin]

Any reason not to use a thermocouple from a multimeter slipped under the radiator hose? I've done this before.

Also, are you sure your gauge is accurate right across the range with a resistor in series?

[Thraxeh]

Any reason not to use a thermocouple from a multimeter slipped under the radiator hose? I've done this before.

i didnt have one.

Also, are you sure your gauge is accurate right across the range with a resistor in series?

Its not accurate accross the whole range, i have made it accurate from 80-100 degress though.

[Mos]

most cars run in between 95-115 celcius. most jap cars run on the hotter side for efficiency. it really depends on the engine. i know the old clunker VN buick engines operate at 105!

Could you please elaborate on the running temperatures you mention?

In my understanding, the thermostat opens at 82 degrees C, so the coolant will start flowing through the radiator, and then any thermo fans usually switch on at 92 or 95 degrees.
In theory the temperature in the radiator should not get much above the thermo fan switch on temp, unless you're producing so much heat the radiator can't get rid of it in time.

Just curious as to where the 95-115degrees C is and how it correlates with the radiator temps.

Mos.

[74sLeeka]

i thought so too, and i assume my gauge is celsius, and it runs at 80.. and any higher than 95 (when i had a leak) and my car made noises..

i lost (took it off and forgot to put it back on) my cap one night, and drove to tafe and back the next morning (20 mins each way) without realising it wasnt on there ! not that i was pushing my car to its limit, but all seemed normal. but it was cold before startin each trip

[Thraxeh]

under normal driving it stays at 85ish, yesterday i did 1 hours constant driving and it got to 93ish when stationary then fans kicked in, then dropped back to 85 when i started moving again.

seems to make sense to me.

[74sLeeka]

exactly ! how do u get 'normal operatin' temps between 95-115 ??

my gauge only goes to 120...

[BeRad]

it seems theres alot of people answering that have little idea about the subject.....

[IN 05 NT]

it seems theres alot of people answering that have little idea about the subject.....

agreed...........

[cressida_1jz]

The best way too calibrate your temp switch is to warm the car up to operating temp,then take the cap off with caution(use a towel) then start the car back up and stick the probe in the filller neck.

And yes u can start the car up with no cap,but dont drive it.