If the car only overheats at 100kmh +...

Does that mean :

- the radiator is gone
- thermostat is gone, or is stuck shut?
- water pump
- something else?

Cant get my head around what it could be, I flushed out old coolant, and refilled it with new.

Car doesnt overheat what so ever with town driving, stop and start, 90km<

But once Im on the freeway, if I go over 90-100, or go up hills, car overheats straight away

What could it be? Yes I am taking it to the mechanic but want to be weary of what is going on incase they give me some story to rake in more $$

cheers

I would remove the thermostat to check if it has failed shut. Also, is your waterpump working fine?

Not sure Aaaron man, how can I tell if the waterpump is gone? I forgot all about that one aswell

When you replaced the coolant and bled the air out with the engine running, was there flow through the radiator filler hole? You can see the coolant flow past if the water pump is working.

Simple checks you can do before taking to the mechanics:
- Stick your head under the car and look for obvious leaks.
- Check that the radiator cap gasket is intact (this doesn't mean the cap is ok! It may not be drawing or releasing from/to the expansion tank).
- Check expansion tank/overflow bottle hose isn't pierced (to the radiator cap spout).
- Check for air in the system (bleed air out correctly - search DIY's).
- Check thermostat is opening - After a decent drive (~10mins or so); carefully put your hand on the bottom hose and check the temperature in comparison to the top hose. If the top hose is hot and the bottom hose is cold (or cool) there's a fair chance your thermostat is not opening.
- Check radiator for blockages and/or efficiency - As with the thermostat check; when hot (if you can get to it) place your hand flat on the radiator fins at the top of the radiator, then at the bottom of the radiator - if there is a massive temperature change the radiator could be blocked.
- Check that the radiator fan is cycling on and off (when engine is warm - at idle).

Could be an individual component, as above or build up in the system causing a blockage.

I'd say it's overheating only on highway or hills simply due to being at higher revs than normal.

Engine works harder = makes more heat.

Let us know how you go.

omgzilla... Yea I know engine gets higher rpm = more hot, but I didnt seem to have this problem before..

So aaron ,if I turn my car on, take the cap off ,and if I cant see the coolant travelling in a circular motion, it means somethings blocked?

Quote:

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Originally Posted by Chriskoss

omgzilla... Yea I know engine gets higher rpm = more hot, but I didnt seem to have this problem before..

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Cooling systems components fail after time dude. Just need to try and keep on top of it before they do more damage.

Quote:

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Originally Posted by Chriskoss

if I turn my car on, take the cap off ,and if I cant see the coolant travelling in a circular motion, it means somethings blocked?

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It could be a blockage or also indicate that the pump isn't pumping.

Addition to original post: fluid won't flow in circular motion - when looking through the radiator cap spout it should travel one way or the other (read: left/right - not circular/clockwise etc).

Dannggg.. I dont believe I saw the coolant mixture travelling

Is it safe to turn my car on while cold, take the cap off, and watch the coolant on idle..

Is there something to do with the heater being on aswell when doing this?

Quote:

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Originally Posted by Chriskoss

omgzilla... Yea I know engine gets higher rpm = more hot, but I didnt seem to have this problem before..

So aaron ,if I turn my car on, take the cap off ,and if I cant see the coolant travelling in a circular motion, it means somethings blocked?

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Not exactly a circular motion, You should see some flow of coolant when you take out the cap. Stick your finger in and even try to feel the flow

Quote:

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Originally Posted by Chriskoss

Dannggg.. I dont believe I saw the coolant mixture travelling

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Is the radiator full of coolant/water though? It will have to be full in order for you to be able to see the 'flowing' effect.

Quote:

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Originally Posted by Chriskoss

Is it safe to turn my car on while cold, take the cap off, and watch the coolant on idle..

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Yes, actually better to do it when its warm, but not HOT - opening system while hot will scald you!

Quote:

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Originally Posted by Chriskoss

Is there something to do with the heater being on aswell when doing this?

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It shouldn't make any difference having the heater on when checking for coolant flow from the pump.

Having the heater on will expand the system or allow the coolant to flow through the heater box aswell as the motor etc. When the heater is turned up and the interior fan is on this helps pull heat away from the cooling system - in turn lowering the overall engine temperature.

When bleeding the cooling system the heater should be on and interior fan on aswell.

most common cause of overheating during highway driving etc is the radiator being partially blocked. Over the years sediment builds in the cooling system and finds it way to the radiator where it builds up from the bottom up, partially blocking it and reducing its effectiveness. Flushing wont get rid of this type of sediment, the radiator needs to be removed, taken to a radiator shop and they will professionally clean it. Or replace it if your extreme or want an alloy one etc.

Easiest way to tell is get the car to operating temp and (depending where your fans are!!!!watch out they can go even if the car is turned off!!!) try to get your hand on the radiator core fins and feel if there is a great temperature difference between the top of the radiator and the bottom, the top will prob feel to hot to hold your hand there for over a second or so, but if blocked you should be able to hold you hand on the bottom for atleast a few seconds or longer if really blocked.

Like i said watch out for the fans. I'm not saying this is definitely your problem, just saying that at our workshop this is the most common cause of overheating at high speeds

Sounds right to me mechanic, I only bought the car not long ago and the coolant looked real old, so I assume its now blocked because of not being cleaned alot.

Where is the thermostat just for good measure is it at the end of the top radiator hose?

I just want to know what it could be before some shop says its 500 bucks for a new radiator etc when it could just be a cheap fix like a new thermo