[Jezza86]

Do all jimnys get stupidly hot engine bays driving at 100kph or just mine?
drove round 100 k of highway and got home to find the bonnet stay bar was so hot i could barely touch it and the windscreen washer bottle water was hot. engine was reading normal temperature and as the cars only done 5000k i wouldn't expect it to be mechanical...

Radiators full, still hot with a winch bar on now. its getting that hot im seriously considering a bonnet scoop.

[zooky08]

My bonnet gets really hot that I can't touch it, and there's nothing wrong with mine. So I say yes it's okay.

[monley]

zooky08 wrote:

My bonnet gets really hot that I can't touch it, and there's nothing wrong with mine. So I say yes it's okay.

x2

[Moag]

Yep even with the back rubber seal removed and the back lifted 1cm to give another path to let the hot air out.

40?C plus is the normal ambient temp up here at the moment though.

[steak_knife]

Normal....

[Jezza86]

cutting a hole in my bonnet and fitting a scoop will mean i need a mod plate?

this will come second to getting my winch clutch to fully engage without the aid of a wheel spanner...

[SLYjoel]

You wouldn't want a scoop anyway, you want a vent just behind the radiator to extract the hot air.

[MacDaddy]

SLYjoel wrote:

You wouldn't want a scoop anyway, you want a vent just behind the radiator to extract the hot air.

X 2
A scoop is for getting air in, not really out, my GV gets extremely hot under the bonnet when 4wheelin, so i was looking at these -
http://www.ebay.com.au/itm/190625580190 ... 1438.l2649
And mount two of them half way up the bonnet, facing backwards, just inside the bonnet lines, i like stainless steel, but there are quite a few fancy bonnet vents on ebay, just do a search...

[Scales]

yeah mine gets epic hot also just even around town. cant touch the bonnet support sometimes. considering getting one of those engine temp monitor things off ebay to keep an eye on it on those hot qld days.

http://www.ebay.com.au/itm/SUZUKI-ENGIN ... 2a14c9db8d

[alien]

my sierra does the same and always has... i lifted the bonnet but retained the seal at the back, so more air is forced in the front - some of which escapes out the sides of the bonnet through the slots at the back, but mostly its forcing the air down past the engine and under the chassis.

Most suzukis are set up like that, that the top is a high pressure area and air is forced over the engine from above. Putting a vent in or opening the back of the bonnet might cool the bonnet, but it could raise the engine temp.

[royce]

the base of the screen - back of the bonnet is a high pressure area, thats why the ventilation intake is there and rear facing scoops like those fitted to the A9X and Brock Commodores worked, lifting and vents etc likely force air into the rear of the engine bay and disturb flow at speeds.

also remember that you arent sposed to have any kind of scoop or vent that can allow engine fluids onto the screen

[MacDaddy]

royce wrote:

the base of the screen - back of the bonnet is a high pressure area, thats why the ventilation intake is there and rear facing scoops like those fitted to the A9X and Brock Commodores worked, lifting and vents etc likely force air into the rear of the engine bay and disturb flow at speeds.

also remember that you arent sposed to have any kind of scoop or vent that can allow engine fluids onto the screen

Yeah that damn law is a PITA... but i also find it strange, because a forward facing, bonnet level scoop, can also allow fluids onto the windscreen, it will just squirt out and blow back... if i could find some of those stainless steel vents, with a sliding opener/closer, that would be good... but if i do fit them, i will plead ignorance...

[dogbox]

i notice on mine that the bonnet is steamming on rainny days so it must be hot

[SLYjoel]

royce wrote:

the base of the screen - back of the bonnet is a high pressure area, thats why the ventilation intake is there and rear facing scoops like those fitted to the A9X and Brock Commodores worked, lifting and vents etc likely force air into the rear of the engine bay and disturb flow at speeds.

also remember that you arent sposed to have any kind of scoop or vent that can allow engine fluids onto the screen

Yep, that's why I said to have it mounted just behind the radiator.

Topstage in Melbourne used to make a more compact version of this vent but I can't find it now. This is the sort of thing you are after. Makes a massive difference to water temps too.

[Jezza86]

yeh that kind of thing would be awesome. i figure that no engine bay really needs to be so hot that you can see the steam coming of the water when you use your dog washers...

my dad mentioned that they used to put washers between the hinge and the bonnet and that would lift the bonnet 1-2 mm at the back, leting a bit more air out there. he reckons that made his old cars run heaps cooler.

[Scales]

thats what moags got.... sorta

[SLYjoel]

Jezza, lifting the rear of the bonnet will only help when stationary.

As Royce mentioned, that part of the bonnet/windscreen is a high pressure zone, so you will actually be drawing air in to the engine bay when moving, creating unwanted turbulence.

[Moag]

Yep I think I've done it wrong!!!

Read a heap of Google stuff and a couple of papers and a thesis on the subject that shows me this is a very complex thing indeed, but there might be some solutions with a bit of experimentation.

It is mainly about pressure differences at speed and fan efficiency at low speeds.

lets have a look at pressure first with a few picks...



This a computer generated model of pressure areas and flow vectors on a range rover,
with red being high pressure areas, blue is low pressure areas and green being neutral areas.

Not having the skills and modelling software, with a good dash of guess work,
this is were i think the main pressure zones are on a Jimny...



A quick rough and ready rule is that air flows from high pressure areas to lower pressure areas.
So we need a high pressure area in front of the radiator and a low pressure area behind for air to flow without it being pushed or pulled by a fan.

One of the first mistakes I made was reducing the high pressure in front of the radiator by whacking a bull bar and lights in the high pressure area obstructing the flow.

The second mistake was not having that plastic guard thing under the bumper below the radiator, "though it came pre ripped off on mine".
I think this was meant to smooth the airflow under the car and create a low pressure area just behind the radiator, which is a great thing to have i think.
Ideally we need the engine bay area to have low pressure with the lower the better.
Basically the engine bay is a box with an opening at the front with a high pressure area (grill) as well as an open area underneath that needs to be low pressure for air to flow.

Some links to a dude that did the experiment...Undertrays,Spoilers and Bonnet Vents...Part 1....Part 2....Part 3

So my thoughts are to make a front skid plate under the bull bar and some sealing around the radiator.

[wolf_rt]

Quote:

The second mistake was not having that plastic guard thing under the bumper below the radiator, "though it came pre ripped off on mine".

this thing supplies most of the airflow to the radiator. the air hitting the grill is moving too fast at highway speeds to pass through the grill.
The 'S' bend the air goes through when picked up by the 'spoiler' slows the air enough to pass through the radiator and provide effective cooling.

Think of an EF falcon...NO grill, all air to the radiator is provided by this 'spoiler'

[Scales]

I was thinking about this issue again today, what are your thoughts on this sort of addition to what is a pretty standard Jim bullbar around here? rekon it would be easy enough to achieve?

[jonno_racing]

i read this thread and did some experiments the other day.

i took the jimny round town and the bonnet was mildy hot. defently touchable in all aieriars.
very simmilar on high way, yet slightly cooler..

my jim has a GHEY bonnet scoop


i have been looking for a new bonnet as mine is cut though.. however i may end up keeping it to keep temps down.

[Scales]

be interesting to see how hot yours is with a bullbar, and move those spottys to the front of the main grill..

I like your checkerplate though.

[zooky08]

I have a bulbar and winch and big light force blitz spottier, and mine gets fairly hot.
Can only hold your hand on for a few seconds before you get burnt. But my temp still only sits around 1/4

[Scales]

yeah same here mate, thats with arb bar and lightforce 170's. same as that blue one in the article above. i dont have a gucci bash plate/air deflector on the bottom like him though.

[atari4x4]

jonno_racing wrote:

i read this thread and did some experiments the other day.

i took the jimny round town and the bonnet was mildy hot. defently touchable in all aieriars.
very simmilar on high way, yet slightly cooler..

my jim has a GHEY bonnet scoop


i have been looking for a new bonnet as mine is cut though.. however i may end up keeping it to keep temps down.

maybe try taping up the letterbox hole & do another test to see if it's actually helping?

also is the hole cut so you can turn the whole scoop around the other way so it's evacuating the hot air?

[jonno_racing]

I might give it a go when I get a chance.
mine no longer has all the checker plate and lights etc till I get a new front bar.

[Total_Filth]

Scales wrote:

I was thinking about this issue again today, what are your thoughts on this sort of addition to what is a pretty standard Jim bullbar around here? rekon it would be easy enough to achieve?

Does anyone know which issue of 4x4Action this was in? Id be interested in reading it.


Cheers,

TF

[jimny_timmy]

It was a while back mate, was a custom version I think... I have it laying around somewhere I think if you'd like me to scan it for you?

[Total_Filth]

That'd be ripper if you could mate. I would really appreciate it.

Email through to jordybowen@gmail.com


TF

[jimny_timmy]

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