Can you remove a radiator cap when an engine is hot?

I was cutting grass over the weekend in an area that had run wild with half a seasons growth. The Tractor is Kubota B7001 and I have a 48 inch (1.2 metre) wide two bladed rotary attached via the three point linkage, run from the power take off. In places, the grass was non-existent and weed with woody stems had overgrown the area so it was pretty hard graft for the machine. I managed high 1st gear but it was still slow and took three and a half hours to complete. The engine worked hard. I stopped for a drink of water and I cold hear the radiator gurgling and I suspected that I was boiling up slightly (although no steam was coming out of the rubber vent tube). I had replaced the fan belt in the spring and also the radiator cap because of overheating. I waited what I thought was a reasonable time (a sort of mental risk assessment) before gently turning the cap using my sweatshirt as a rag. I got the cap to about three quarters and I heard the vent 'exclaim' as the pressure released. Thinking I was now at a safe point to release the final turn I continued but I was shocked at the next bit (although my risk assessment had flagged up the possibility). As I reached the 'gateway' to the cap there was an enormously loud whoosh as the cap gave way and the (still considerable) steam blew up. The cap left my hand as I turned away and I threw myself on the ground as boiling hot water and steam hit me with some force in the side of the head (much was deflected by the bonnet of the tractor which was poised at 45 degrees above the radiator). I rushed to a tap and doused myself with cold water (about three -five mnute delay). The burning sensation was extreme for a few moments. The side of my head was painful for the rest of the evening and my skin curled up in a spot the size of a golf ball. I was falsely led to think that all the pressure had gone. This is the first time this has happened to me. Next time, I will go and have a cup of tea rather than a swig of water.

Hi Phil

obviously you have established the answer.

I assume the cap is the modern day screw thread type which is not user friendly when it comes to removing under pressure.

Years ago the radiator cap would tighten down and transversely release with a quarter or half turn.
The cap also had two lugs sticking out, which meant the cap could be turned by pushing a lug with a long piece of wood. Would send the cap 10 feet in the air but it didn't matter as you were several feet away.
I assume the cost of production now dictates what is fitted as opposed to the more important safety aspect.

It was obvious back then that people could miss judge the temperatures involved or that people would just be to impatient. So why is it not mandatory to have a cap which has a built is safety element. I know its going off the subject a bit but you were very lucky not to have sustained serious injury. And for what? A few pence on the cost of an engine/vehicle.

Replies

Richard Boyd October 12, 2009 at 3:29pm

Can you remove a radiator cap when an engine is hot?

Yup, but very slowly!!! :)

Sorry to hear about your head, I too have joined the walking wounded after an Olive tree swung off the tail lift at a strange angle and a branch decided it would rather be part of my head than attached top a tree.
chris nangle October 12, 2009 at 4:23pm

Can you remove a radiator cap when an engine is hot?
I think you have found out the hard way that its best not to mate!
hope you get better soon philip
Kieran Ray October 12, 2009 at 6:25pm

At colege we were always told not to! and on every thing I have owned it said not! So I never have done. And im glad as it sounds very painfull! hope your going to be ok Phil!?
PRO

Phil Voice October 12, 2009 at 6:26pm

Thanks Colin

I do think part of the problem is the absence of coolant - after losing water before the radiator cap and fan belt change, I haven't replaced it. Must do so soon, even this evening feels as though a slight frost could occur.

No hydrostat :( it's a Chinese import manual gears.
PRO

Phil Voice October 12, 2009 at 6:29pm

Thanks Kieran

I'm fine if not a bit embarrassed for being so complacent. Not to proud to share my mistake with a few thousand people if it helps them to avoid a potentially dangerous situation.

I thought I had left it long enough but it made me realise that the water temperature/pressure remains high for quite a while.
GORDON October 12, 2009 at 7:29pm

Hi Phil

obviously you have established the answer.

I assume the cap is the modern day screw thread type which is not user friendly when it comes to removing under pressure.

Years ago the radiator cap would tighten down and transversely release with a quarter or half turn.
The cap also had two lugs sticking out, which meant the cap could be turned by pushing a lug with a long piece of wood. Would send the cap 10 feet in the air but it didn't matter as you were several feet away.
I assume the cost of production now dictates what is fitted as opposed to the more important safety aspect.

It was obvious back then that people could miss judge the temperatures involved or that people would just be to impatient. So why is it not mandatory to have a cap which has a built is safety element. I know its going off the subject a bit but you were very lucky not to have sustained serious injury. And for what? A few pence on the cost of an engine/vehicle.
Richard Boyd October 12, 2009 at 10:45pm

Got a photo Phil? I'll swap you, my head has stopped bleading and despite everyones efforts to ship me off to get stitches, I don't think it will need it.
Lawncare-4u.co.uk October 12, 2009 at 11:02pm

i think i remember opening / checking the oil on my car once when the engine was still running ! hmmmmm

it was a while ago (where was my mind ) !

i also cut my hand (twice) today fixing the loose inside/car door handle on my shogun '03 : it must've had some use . alcohol wipe and a large plaster dressing from one of my 3 sized first-aid kits and all was ok.

good post phil - i hope your ok (im glad you watered yourself before the tractor) * Your no1 ...

is aloe or comfry good for 'burns' ??
Kieran Ray October 12, 2009 at 11:23pm

Aloe is, we have a big one in the gardenand when ever some one gets burnt doing the cooking they put a bit on it.

Robin Ainsworth said:
i think i remember opening / checking the oil on my car once when the engine was still running ! hmmmmm

it was a while ago (where was my mind ) !

i also cut my hand (twice) today fixing the loose inside/car door handle on my shogun '03 : it must've had some use . alcohol wipe and a large plaster dressing from one of my 3 sized first-aid kits and all was ok.

good post phil - i hope your ok (im glad you watered yourself before the tractor) * Your no1 ...

is aloe or comfry good for 'burns' ??
PRO

Phil Voice October 19, 2009 at 9:37am

Antifreeze changed in tractor and mini digger yesterday - we have had frosts for the last week or more.