Overheating 75 V8

[5Litre75]

Hey guys,
Im currently running a 75 series tray with a fuel injected holden V8 and auto which just will not cool on freeway runs sometimes up to 220F! Ive tried bigger radiators 4 row upright and 4 row crossflow from commodore, cooler thermostats, different fans from fixed to twin thermos and hand made water pumps. Has anyone come across this? Ive also got a bonnet vent in but to no avail. Could it be lack of airflow under the bonnet? would an under tray help to stop the turbulence under the car?
I am at a total loss and a similar financial one at this point.
hope someone acn shed some light on this.

[lambsy]

do you have an auto transmission cooler that is seperate from your radiator? if not, it could be circulating hot oil through your radiator and overheating. if your bands in the auto are sliping this can cause extra heat build up in your trans fluid, an auto service may fix problem?

[nischev]

Where are you running your air intake? Could be just that it is sucking in hot air from under the bonnet which will increase the engine temp causing it to suck hotter air and so on. I was having that problem in my patrol with 327 chev and a snorkel fixed the problem. also you could try running a cooler thermostat as this can sometimes help. The fans wont help as they are basically redundant over about 30kph.

[5Litre75]

no the tranny is on its own cooler and thats all fine the tranny isnt that old ........its got me buggered!

[nischev]

So its the tranny overheating is it?

[5Litre75]

no the tranny is all ok its the engine thats overheating

[nischev]

Ok well i will stand by what i said first thought it was engine but then you got me all confused. :-\

[5Litre75]

the air intake temps are all normal everytime i check with the code scanner they arent anything to stress about its just seems to be one of those problems that wont go away.

[nischev]

Yeh but it does help get cool air in you would probably be surprised by the difference if it is currently just sucking air frm the engine bay. Even as a test you could hook up a dodgy cold air intake to the side of you radiator or somewhere.
Are you sure the temp gauge is accurate.

[5Litre75]

I have three temp guages in it the dash one and one each in the top and bottom hoses plus the one i can pull out of the computer with the scanner.

[nischev]

I have three temp guages in it the dash one and one each in the top and bottom hoses plus the one i can pull out of the computer with the scanner.



Ok fair enough.
I would definatly try getting cooler air into it and also check your mixtures at cruising speed as maybe it running a bit lean.

[5Litre75]

mixtures seem to be fine on both petrol and gas the funny thing is when its in high rev but low speed work ie beach it doesnt get hot. All the while the car speed is down so is the temp ???

[nischev]

Maybe a wild guess but try putting a bash plate under the front half of the engine bay (or bit of rubber for the trial). Could be the air coming under the front circulating back up into the engine bay and stopping proper flow through the radiator. ??? ???

Wild guess but stranger things have happened. :-\

[5Litre75]

Im gonna give the bash plate a shot next ...today i yanked the A/C condensor out and its seems to have made a dramatic improvement sits around 180F to 190F but nothing higher hopefully the bash plate will drop it that bit extra to give it some hot day margin. ;D

i think Stu is on the money with the hot air under the bonnet...... i had a similar problem with my Commondoor....... the little plastic attachment that went from the air filter box to the hole next to the radiator fell off once, and the engine started to run much hotter than normal. Once i found that thing off and put it back on again, it worked fine. It's worth considering.

[2 BRUTAL]

so low range 4WD going real slow doesn't get it hot then.
Strange. :-\
the bonnet scoop could be forcing to much air into the engine bay and then not allowing enough air thru the radiator by pressurising the engine bay maybe.

[ozhumvee]

75 series are renowned for having bugger all airflow under the bonnet at road speeds, something to do with the body shape and the aerodynamics.
I think it was Safari that put one in a wind tunnel and found that there was no airflow as the early 2H engined ones got really hot and cremated the battery, a set of spotties and awinch and bullbar made it overheat too.
I had a 87 2H powered troopy and if the ambient was over 30 it would overheat in 5th gear and a tail wind, chuck it back to 4th and it would be ok.
What happens is that as the air flow through the radiator decreases the thermo coupling on the fan doesn't get hot so it doesn't lock up which leads to the overheating problem.
when you are going slow off road there is no built up air pressure under the bonnet so the air can flow freely through the rad heating the fan up so it works correctly.

[kingchevy]

Have you checked the fan shroud it can be very inportant to it cooling the fan should be sitting out of it 1/3 and it should have 25mm outside gap around the fan and it should be able to suck of every part of the radiater to get effiecent cooling

http://www.pinewood.schoolreference.com/lx450-engine-port.jpg

This is just an example of how a fan shroud should look hope this helps??

[5Litre75]

Thanks for the tips guys Ive heard of the air flow problem and the cooking of batteries etc which is what brought me to the thought of under bonnet air flow. I suppose the V8 engine doesnt help because the air cant flow around it as easily as straight 6. Ill try the under tray and hope it stop the turbulent air under the bonnet building up. The reverse bonnet vent seems to be letting some air out hopefully with the tray it will suck some more out. Ill keep you posted on how i go when i get some more time.

[HDJ105]

Thanks for the tips guys Ive heard of the air flow problem and the cooking of batteries etc which is what brought me to the thought of under bonnet air flow. I suppose the V8 engine doesnt help because the air cant flow around it as easily as straight 6. Ill try the under tray and hope it stop the turbulent air under the bonnet building up. The reverse bonnet vent seems to be letting some air out hopefully with the tray it will suck some more out. Ill keep you posted on how i go when i get some more time.


5litre75,

It certainly sounds like an airflow problem as others have mentioned. If you can work it hard going slow without it getting hot then the fan must be working fine.

Why did you fit the bonnet scoop, was it to try to fix this problem or fitted for clearance / cosmetic purposes when the conversion was done?

As an experiment try taping some strips of ribbon or something at the exit of the bonnet scoop as an indication or airflow direction, and see which way they move while you drive up the road at various speeds. You could also try some spacers to lift the rear edge of the bonnet up (like many have done on Nissan's) to see if it helps with airflow.

It may also be worth visiting a Toyota dealer and looking at a new TD 79 series cooling system to see if Toyota fitted any extra air deflectors or tray to assist with cooling.

[5Litre75]

i have tried the string trick on the vent and its pulling air out of the engine bay. I tried lifting the back of the bonnet but being a high pressure area ( as the wind hits the windscreen it causes an air back up of pressure.....hence why fresh air vent for the cabin are there...to take advantage of the pressure) but it didnt help any.

[HSV Rangie]

Do you have a fan shroud fitted CORRECTLY.

This mandatory.

You must ensure full flow of air from grill through rad and it will dissapate out under car.

Michael.

[5Litre75]

Its running twin thermos from a mondeo which was far better than any engine fan i run.

[HDJ105]

Its running twin thermos from a mondeo which was far better than any engine fan i run.


Are the thermo's running at highway speeds? They may be causing a restriction to the airflow by not passing enough air mass?

[roc70y]

you don't have 2 massive lightforce lights blocking the air flow by any chance do you???

[HSV Rangie]

I run thermos from EL ford on the RR and all is welll, the shroud has been adapted to the rad so all air is pulled through the rad.

what else is blocking air flow in your system.

Michael.

[Yetti]

hey dude just sorted out my cooling problems on my injected 5litre 220 is way to hot it should run at 180-190 i got a cooler thermostate and a fixed fan (no clutch) from a 70 model 2f cruiser engine and a holden HQ shroud and the radiator is from a 60 series cruiser diesel 4 row now i have trouble getting it up to 190 so i will change the thermostate back

[5Litre75]

Im running a cold 76C thermostat and a 4 row. The biggest problem with the 75 series is the narrow nose which restricts the size radiator i can jam in there. Its running a cross flow from the commodore because the 4 row cruiser rad just wasnt up to it .....flowed thru the core too fast. The cross flow gives it longer time in the core to cool.....but since removing the A/C condensor its running around the 180-190 mark but id like some more for hot days.....hence why the under tray will be next.

[Yetti]

i really encourage you to put a 70 model plastic fan off a 2f cruiser engine and a good shroud as this puls shit loads of air it will drop it by shit loads i now need to get the standard thermostat cause if you drop to much below 180 you use to much fuel the ecu thinks its still cold

[5Litre75]

If it drops too low then ill put a hotter thermostat in it but while its running LPG the cold doesnt worry it too much as the computer cant adjust the gas flow......that said ...on petrol its terrible but its having a new chip done soon so that will square that up.

[Yetti]

sweet what power are you going to get out of the chip and how much is it costing

just out of curiosity which side of the radiator are your thermos on and are they sucking or blowing? the part about how it runs at an okay temp at low speeds while revving hard ie low range makes me think you have an air flow prob related to your fans. If for instance they are on the engine side of the radiator and are wired up to blow not suck, then when travelling at speeds it causes the air to stop in the radiator basically and will over heat it. I have seen this twice on cars that have had engine conversions, might not be your problem but still a good idea to check ;)

[5Litre75]

they are on the engine side and they are sucking for sure. The fuel economy is only part reason why im getting a chip done i have a spare engine with flat tops roller rockers and a cam etc to slot in mainly for a bit more torque than overall horsepower. Ill see how i go im hoping somewhere 230-240KW nothing huge.