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GU under load = over heating?

General Tech Talk

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GU under load = over heating?

Post by Glennb »

Hi all, I have a GU 4.5ltr petrol auto on gas.
it will only over heat(up to around half way and air con turns off) in these conditions.
only on days 33degress+, only under load (slight incline in road) and/or at low speed in low range up a hill and/or city driving when accelerating.
When cruising on the flat all is good EVEN if I drive it with the OD off with higher revs.
Even if i drive in 3rd at 2400rpm at a 100kph on the flat the car is fine but 30sec or so after the car hits a incline it will start heating up to just past half way without the revs moving at all staying on 2400rpm. :? how is this possible?
car will cool down and/or stay cool,when slowing down , stationary at the lights, cruising on a flat road at any speed, no problem at all if out side temp is below 33C.
cheers
Glenn
edit: more detail on m next post.
Last edited by Glennb on Sun May 30, 2010 12:10 pm, edited 1 time in total.
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DamTriton
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Post by DamTriton »

Have you had the ignition remapped at all?

It it run solely on gas?

IIRC you need to advance the ignition timing on gas due to it's slower flame propagation Late timing means the energy is simply converted to heat late in the pistons cycle rather than into energy at/near TDC.
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Post by nabstud »

Have you checked the basics? Coolant level, belts adjusted, nothing blocking the radiator, no kinked hoses, thermostat working?

Sounds like a coolant flow problem, probably radiator blocked. First thing I would do is taking out the radiator and get it thoroughly cleaned/rodded.

Many things to try and eliminate. Thermostat, radiator cap, viscous fan coupling, fan belts, hoses, maybe the head/head gasket is gone...
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Post by ludacris »

Radiators should be changed reconditioned every 8 to 10 years. Your fan may need changing as well.

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RAY185
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Re: GU under load = over heating?

Post by RAY185 »

Glennb wrote:it will start heating up to just past half way...
If this is as hot as it gets I don't think you really have a problem. Possibly slightly blocked radiator if anything.
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Post by Glennb »

I should of stated that the radiator is only 2 years old, thermostat works fine, did a coolant change last summer and problem still there. All fan belts are fine etc.Gas has its own computer and the problem also happens on petrol.New radiator cap and I dont loose any coolant.
What I dont under stand is why I can have the revs up high and it will not over heat and then hit an incline the revs dont move at all and then the car will heat up??
Can anybody explain why revs can stay the same and why an engine WILL WANT to heat up more when under load though the revs will stay the same?
Also when a thermostat opens, does it open fully when it hits a certain temp or will it only open to a certain size to temp.(e.g 1/4 open 80C, 1/2 open 85C...so on) Thinking it could be sticking at 3/4 open if this is how they work?
Cheers
Glenn
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Post by shakes »

thermostat could be sticking.. but unlikely, I'd more look towards the viscous fan not engaging properly? are they servicable on these cars?
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Post by Glennb »

shakes wrote:thermostat could be sticking.. but unlikely, I'd more look towards the viscous fan not engaging properly? are they servicable on these cars?
I presume the viscous fan is the one on the front of the radiator? It does click on and off when the air con is on, but have not taken much notice of it any other time. Would the fan make any difference at 100kph?? also the car cools down fine at the lights if it was running hot before hand.
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Post by shakes »

Glennb wrote:
shakes wrote:thermostat could be sticking.. but unlikely, I'd more look towards the viscous fan not engaging properly? are they servicable on these cars?
I presume the viscous fan is the one on the front of the radiator? It does click on and off when the air con is on, but have not taken much notice of it any other time. Would the fan make any difference at 100kph?? also the car cools down fine at the lights if it was running hot before hand.
the one on the front of the radiator is more likely to be purely for the a/c

the big engine fan off the front of the motor. I'm not super familiar with these motors so it's only a guess but the oil needs changing in the fan. which is something I had to do on the 4.2.
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Post by Glennb »

shakes wrote:
Glennb wrote:
shakes wrote:thermostat could be sticking.. but unlikely, I'd more look towards the viscous fan not engaging properly? are they servicable on these cars?
I presume the viscous fan is the one on the front of the radiator? It does click on and off when the air con is on, but have not taken much notice of it any other time. Would the fan make any difference at 100kph?? also the car cools down fine at the lights if it was running hot before hand.
the one on the front of the radiator is more likely to be purely for the a/c

the big engine fan off the front of the motor. I'm not super familiar with these motors so it's only a guess but the oil needs changing in the fan. which is something I had to do on the 4.2.
cheers,
did some searching and yes the main fan seems to be working fine.
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Post by BadMav »

If the auto has the cooler lines running into the radiator tank and the auto is slipping (which it sounds like it is), this could be your overheating problem. I never liked the in tank cooler idea on any car. I always run an external oil cooler for the auto. Has it been a while since the auto was serviced? You might want to get it checked/serviced.
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Post by Glennb »

BadMav wrote:If the auto has the cooler lines running into the radiator tank and the auto is slipping (which it sounds like it is), this could be your overheating problem. I never liked the in tank cooler idea on any car. I always run an external oil cooler for the auto. Has it been a while since the auto was serviced? You might want to get it checked/serviced.
This makes sense but wouldnt my revs go up if the trans was slipping?and also why only 33C+ days.
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Post by BadMav »

It's worth a look see. At least if it isn't you can rule it out.
Last edited by BadMav on Mon May 31, 2010 5:15 am, edited 1 time in total.
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Post by Guy »

My GU had similar symptons .. radiotor had one "air passage" through it where the main engine driven fan was. The rest was soild with silty mud.

Radiator comes out pretty easy.. I would be pulling it and washing out the fins. Its quick, easy, low cost (new coolant but thats not terribly expansive and it is over 12 months old) and if nothing else you can eliminate two thing as suspects.
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Post by macneil »

also when you take your radiator out run a different water to coolant mix... right now your probably running 50/50?? maybe run 35/65 bit more water may help it cool...
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Post by howsie »

might be silly but it sounds to me like an electrical problem with the temp going up and down with revs. Maybe hook up an aftermarket gauge and see if it does the same thing. Its happened to me before on a ea falcon
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