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under-bonnet temps (cooling)

General Tech Talk

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under-bonnet temps (cooling)

Post by alien »

Any ideas on cooling under my bonnet??? Car is a sierra running vit 1.6 EFI and has a snorkel.

at speeds below 20km/hr or so, or above 100km/hr my engine temp goes up a fair bit... i've got a thermo fan which controls the slow speed stuff, but theres obviously too much heat in the engine bay thats not being dispersed. I'm assuming this is due to the 1.6 sitting closer to the bonnet, as well as the snorkel hose and battery blocking one of the standard vents on the side of the bonnet.

Its been suggested i use thermal tape on the extractors, but i hear this shortens the life of them considerably?

I was thinking of adding a vent on the top of the bonnet but it seems most people say this will have the opposite effect on cooling the engine bay, and that the air needs to exit from underneath?

So, whats the best thing to do here??? =)
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Re: under-bonnet temps (cooling)

Post by guzzla »

Has this 'overheating ' been an issue right from the start or only just recently?

If it's the latter, then the cooling system is most likely at fault and in need of attention/repairs.
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Re: under-bonnet temps (cooling)

Post by chimpboy »

As above, I would look first at what's already there. What is the current fan set-up, is the radiator cowled properly, etc? You might also be able to add a small spoiler at the front (eg just a piece of bent metal) to get a bit more flow through the radiator and a better low pressure zone under the engine bay.

Then of course... is the radiator big enough? Is it the sierra rad or did you put a vitara one in or...?

If it does come to putting in vents, you can sometimes experiment by spacing up the rear end of the bonnet to create a 10mm or so gap and drive around that way to see if it helps. But I would focus on the other stuff first.
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Re: under-bonnet temps (cooling)

Post by St Jimmy »

Cool air
One possible use of a hood manifold. In most modern automobiles, internal combustion engines "breathe" under-hood air or air ducted from under the front bumper through plastic and rubber tubing. The high operating temperatures in the engine compartment result in intake air that is 28°C (50°F) or more warmer than the ambient temperature, and consequently less dense. A hood scoop can provide the engine with cooler, denser outside air, increasing power.

Ram air
At higher road speeds, a properly designed hood scoop can increase the speed and pressure with which air enters the engine's intake, creating a resonance supercharging effect. Such effects are typically only felt at very high speeds, making ram air primarily useful for racing, not street performance.

Pontiac used the trade name Ram Air to describe its engines equipped with functional scoops. Despite the name, most of these systems only provided cool air, with little or no supercharging effect.

Intercooler scoops
Some engines with turbochargers or superchargers are also equipped with top mounted intercoolers to reduce the temperature and increase the density of the high-pressure air produced by the compressor. Channeling outside air to the intercooler (which is a heat exchanger similar to a radiator) increases its effectiveness, providing a slight improvement in power.

Scoop design
To be effective, a functional scoop must be located at a high-pressure area on the hood. For that reason, some functional scoops are located at the rear of the hood, near the vehicle's cowl, where the curvature of the windshield creates such a high-pressure zone, and may be placed so that their opening faces the windshield (a reversed scoop).

The scoop will be most effective if it is either mounted high enough to clear the boundary layer (the slow-moving air that clings to the surface of a moving object) or if it is a "NACA duct," mounted below the surface and designed to draw the faster moving air outside of the boundary layer into the duct. A shallow scoop that is not a NACA duct may not admit a useful amount of air even if it is open.

Under the hood, an effective scoop must funnel air into the engine's intake in as short and direct a path as possible, preferably through a tub or channel that is insulated against underhood heat.

A scoop may be part of the hood, or may be part of the engine's air cleaner assembly, protruding through a hole cut into the bonnet. Such a scoop is called a shaker hood, because the scoop vibrates noticeably when the engine is running, especially under power.

Hood scoops and off-road racing
A hood scoop/top mounted intercooler can be beneficial, especially during an off-road rally race. Rocks and debris can be kicked up by a car in front, and those objects can damage a front mounted intercooler. However, rock guards can be installed to prevent this problem.
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Re: under-bonnet temps (cooling)

Post by Rangie Thing »

on the old cortina's we fitted spacers at the back of the bonnets to give 10mm gap that helped out .
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Re: under-bonnet temps (cooling)

Post by alien »

its a sierra radiator (acutally its a maruti one - plastic top tank)... standard engine fan is in place as well as a 10" thermo (manually switched).

the problem has been an issue since going EFI, im assuming the power increase also comes with a temperature increase.

the cooling system is all quite new, so theres no issues there - like i said in the OP, it only gets hot under 20km/hr or over 100km/hr, which is what leads me to believe its an airflow thing (air not escaping under the car).

i definitely don't want a bonnet scoop - that just makes for cop bait as well as obscures my vision (even if only slightly).
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Re: under-bonnet temps (cooling)

Post by gingerbreadman »

if your overheating below 20 and above 100 i dont think its your engine bay temps causing the trouble.

slow speed heating issuse come down to insufficient radiator , or mechanical airflow.
high speed heating issues come down to insufficient radiator, timing and poor natural airflow.

i dont know what thermo fan or engine fan your using but if its not a spal thermo than it more likely needs a shroud. spal 2500-3000cfm fans are the only ones i have seen that pull enough air to work without a shroud. is your mechanical engine fan shrouded ?

on the point of thermo fans if its on when your at cruise speed than your actually restricting airflow, not increasing it. For your cooling issues at 100 i would be looking at your radiator seals and making sure all the air that can possobly flow through it is flowing through it and not finding a path of less resistance. if air can flow around it then it will. Your high speed issue may also be a timing/ mixture issue and any radiator fan /combo cant keep up with that.if you can post a pic of your set up and lets see if we can spot anything.

one last point is do you have a 1/8 hole drilled in your flat part of your thermostat to allow any air to dispell ensuring when you top up your radiator its all coolant and not an airloc.

this spal actually does have a shroud but its hardly worth mentioning its that small. in most cases a proped shroud will be needed that draws air through the entire radiator.

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Re: under-bonnet temps (cooling)

Post by alien »

here's a recent pic:
Image

you can see the radiator through the barwork, the thermo fan is in front of the radiator, and the factory fan behind the radiator. all factory shrouds are in place.

perhaps the air is going around the sides rather than through the rad? still, this wasnt an issue when i was carby and had the same setup (just no thermo fan)... only after going EFI has it had the temp issue - and its just taken this long for me to get annoyed with it.
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Re: under-bonnet temps (cooling)

Post by chimpboy »

It's really the flow through the radiator that matters the most. The optimal set up drives air from in front of the car through the radiator, and at the same time creates a low pressure zone under the car which draws the same air out through the bottom of the engine bay. It doesn't matter if the radiator etc is brand new or not, if there are lots of ways for air to go past the radiator instead of through it.

Sometimes this means putting some rubber/neoprene/shrouding etc around the radiator as well. I would not focus on the airflow around the motor much, it's the ariflow through the rad that matters.

Having said all that if you are running the Sierra radiator with the Vitara motor then your total cooling capacity might just be too marginal now.
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Re: under-bonnet temps (cooling)

Post by alien »

on MrRocky's advice i just took the grille off and blasted my radiator with the garden hose set to 'jet' - got a LOT of dust/mud out of the radiator.

could it be that simple? lol

i'll update later with how testing goes.
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Re: under-bonnet temps (cooling)

Post by gingerbreadman »

alien wrote:on MrRocky's advice i just took the grille off and blasted my radiator with the garden hose set to 'jet' - got a LOT of dust/mud out of the radiator.

could it be that simple? lol

i'll update later with how testing goes.

every little thing counts alien. the dust/dirt not be the biggest problem but it might not be helping. radiator tubes would need to be fairly obstructed to cause a total overheat.
looking at your picture your bar,spotties and number plate would be causing a sl ight obstruction at cruise speed but at idle or less that 20 kph they dont come into play. i would look at mounting your spotties slightly different to be not block the airflow possibly down under your normal lights and it looks like your number plate could go slightly lower as well but that may not change anything ..bit hard to tell in the pic if its needed or not.

do you have a pic from inside the engine bay showing the shroud and fan set up? for a fan to be sufficient you should be able to put your hand on the front of the cars grill/radiator and be able to feel the air pulling through(talking about your mecahnical fan not your thermo). if you can feel it then thats all the airflow you need at low speeds and you can go onto other things.

is there any chance your thermo fan got put back in with reverse polarity after your engine mods and is now fighting against your clutch fan..seen that before.
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Re: under-bonnet temps (cooling)

Post by alien »

thanks mate - yeah it doesnt do "total overheat" it just gets hotter than i want it.. the guage usually reads around 1/3rd, when "hot" it goes to half way.

spotties would be obstructing rad for sure, but the bottom tank on the radiator finishes at the bar below where the spotties mount, so numberplate and bottom of barwork is not an issue.

no pic inside the engine bay, but its all standard sierra mounting under there.

ill try the fan feeling thing when i start it up today- cheers =)
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Re: under-bonnet temps (cooling)

Post by St Jimmy »

alien wrote:
i definitely don't want a bonnet scoop - that just makes for cop bait as well as obscures my vision (even if only slightly).
Don't use scoops go the mil hummer way flutes
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Re: under-bonnet temps (cooling)

Post by guzzla »

Since fitting the EFI, have you had the engine dyno'd to see what the AFR's are? - if it's running too lean, combustion temps will be up and placing too much effort on the cooling ability of the oil and the coolant.

Sometimes, overheating issues are not directly related to a coolant system malfunction but a by-product of an overloaded oil cooling issue.

If nothing else, it'd pay to fit an oil temp gauge to see what's going on.
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Re: under-bonnet temps (cooling)

Post by alien »

i do like the idea of an oil temp guage...

nope - havent had it on a dyno - i suppose i could, although i dont know how much (if any) adjustment a jimny computer has.
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Re: under-bonnet temps (cooling)

Post by gingerbreadman »

along with oil temp , oil pressure i also run a coolant temp gauge as well (all mechanical) even if the car has a stock electric gauges .

it might be worth while getting an IR gun alien and checking what your temp actually is when your gauge goes to the high reading. you might find that its warmish but within specs. I use farenheit gauges for a bit more accuracy and if i ever see it go over 200f i know something is wrong. generally it sits on 185 if i run that thermostat.

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Re: under-bonnet temps (cooling)

Post by alien »

wow - thats a lot of gauges =)

highway test just done - outside temp is 36.7 (at 5pm!)

still heated up just the same - it doesnt go past a certain point, but definitely runs hotter than if doing 60km/hr.

i also did a run at 90km/hr with the bonnet latch popped, so the front of the bonnet was up a bit more jamming more air in the front - this made no difference.

while the engine was warm still i turned on the thermo, after a minute or two it brought the temp down to half way between "normal" and my hot point. i also felt around the engine bay - the pipes are super crazy hot, but so is the engine block (of course) right next to the radiator.

i think i need to get a proper degrees reading of the water temp - perhaps the variance between my "normal" temp and my "hot" temp isnt actually that bad like you say.

whats the easiest way of getting a degrees reading off the coolant?
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Re: under-bonnet temps (cooling)

Post by DamTriton »

Have you got the electric fan wired the right way? They normally supply a wiring diagram for a "puller", what you have in front of the radiator needs to turn the opposite way, ie a "pusher".

Did you orient the blades the right way (both ways will draw air through, only one way will do it efficiently)? Thicker part of the airfoil on the blades should be towards the front of the vehicle.
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Re: under-bonnet temps (cooling)

Post by alien »

haahh yeah when i first put it on i had it backwards (thats how it comes out of the box) - its flipped and definitely forcing air through the radiator.

can anyone recommend a good water temp guage and where to purchase? prefer to buy from a store and i know supercheap are questionable, but how are the 'caliber' brand ones? http://www.supercheapauto.com.au/online ... 48#details" onclick="window.open(this.href);return false;
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Re: under-bonnet temps (cooling)

Post by gingerbreadman »

the best gauge in my opinion is autometer .they arent cheap at about 110 bucks but are pretty bulletproof and there is many styles to choose from . autobarn will sell them at a resonable price but if its worth the hassles the cheapest you will find them in oz is at rocket or vpw speed shops .

here is a link...http://www.autometer.com/" onclick="window.open(this.href);return false;

for about 30 bucks spectre gauges do the same thing and probably give the same results but arent as flashy. repco has specials on them from time to time.they are much like the calibre one you showed but they are electric meaning a sender screws into your block and then it transfers the reading to your gauge via a wire. autometer mechanical gauges actually have a hollow tube filled with gas much like a mercury filled thermometer for accuracy and no electronic failures.

if your not keen on outlaying for a gauge straight up most mecahnic shops will do a quick check with an Infa Red gun for you at no cost just to see what temp your at and thats the easiest way....you just simply point the gun at the radiator tank and it will tell you what it is. shoot a few different spots like your block and radiator hose as well for a more overall idea .

if your pipes are extremely hot then good chance your mixtures /timing on that injection is not right . if they glow red anywhwere thats a definate .

i noticed perth is getting some crazy hot temps of late..thats going to test out any cooling system. i notice over here that when it goes over 30 degrees i may hit 190 on the gauge easily.
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Re: under-bonnet temps (cooling)

Post by alien »

thanks mate - yeah i've been recommended autometer and VDO brands.

i know i can get VDO locally, but not sure if repco in WA sell autometer? hope they do, as theres one down the road.
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Re: under-bonnet temps (cooling)

Post by alien »

well i got a gauge from auto-one - can't seem to get the autometer or VDO.

anyway - got home and went to start fitting it when i had a sudden "bugger" moment - the only outlet on my thermostat housing is connected to a sensor! so the only way i'll be able to run the gauge is if i disconnect that - which i assume is going to upset the computer.
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Re: under-bonnet temps (cooling)

Post by alien »

i took the easy way out =P lol

i just swapped the guage for an IR gun... can just carry the gun in my recovery kit... but i just took readings on the gun compared to my guage and im within spec.

my "normal" temp is 90 degrees, my "hot" temp is 101 degrees.

i also pointed it at the pipes if the pipes are numbered front to back 1 - 4, number 1 at the first bend is 272*C, 2 is 270*C, 3 is 260*C and 4 is 270*C =)

I think im going to have a lot of fun with the gun... lol
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Re: under-bonnet temps (cooling)

Post by gingerbreadman »

sounds good alien. it sounds like a handy tool to have and need to keep your mates hands off that one :) ....215 F (101c) im pretty sure is fine for late model computer controlled cars . wouldnt go any hotter though, but im sure once your weather cools down you should be around the 95 mark.
out of curiosity what the temp on the outlet side of your radiator to see how much it cools through it?
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Re: under-bonnet temps (cooling)

Post by alien »

hahah yeah i think i've already checked the temp of everything in the house, including our pet birds =P
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Re: under-bonnet temps (cooling)

Post by purplebus »

out of curiousity with the new motor did you fit the old sender out of the old motor. i would presume the senders on the eng would " talk " to the dash guage differently and maybe give a false reading in dash. good luck, nothing more annoying than a overheating truck.
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Re: under-bonnet temps (cooling)

Post by alien »

thanks mate - nope - its a new sender hence the discrepancy...

so what previously would have indicated overheating is now just showing a temperature difference of 10*C - normal temp being around 90*C, and what i thought was overheating was 100*C... so all is well =)
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Re: under-bonnet temps (cooling)

Post by chimpboy »

It's good to know it's not going apeshit heatwise. However an optimally functioning cooling system should give you the same operating temperature in all conditions, road speeds, etc.
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Re: under-bonnet temps (cooling)

Post by alien »

^^ true - but crawling around in full sun on a 38 degree day is a bit much =) haha

in other news i tested my new toy (IR Gun) on my sunburnt knee... its 3-4 degrees warmer than my non-burnt skin, and measures 34*C =P
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