Avensis 1.8 1999 Intermittent Overheat

[tonos]

Whilst driving a few days ago I noticed that cold air was coming through the heater vents, in spite of the car being up to normal operating levels. During this drive and any other subsequent drives that day, I noticed that the heater appeared to have a mind of its own; one minute hot air, the next cold air.

The same symptoms were evident yesterday.

Today though, things appear to have got worse. Apart from the above mentioned problem, I have noticed that the temp gauge is fluctuating wildly from normal 'middle of the gauge reading' to topping out in the red.

I have so far changed the thermostat and checked for any leaks, but still have the same symptoms.

The gauge readings can go from normal to red, then back again within an unusually short time. Both fans appear to be working. What I have noticed is that when the car is up to normal running conditions, the hose that goes from the radiator to the thermostat housing is warm at the therm end, but cold further down towards the radiator. Whereas the shorter hose is warm along its length.

I hope this makes sense, and that someone out there can help?

[Konrad C]

Wonder if the radiator is blocked, or the system needs a flush. So long as the water pump is working properly. So long as the belt is turning the pump is okay there should be no problems. The pump is a alloy so normally should not break. Check for leak from the pump, especially during warm up and cool down. There may be drips under the car after a few minutes. Look at the engine block core plugs.

Does the system need bleeding? You may have an air lock.

Is coolant level dropping in the expansion bottle and the radiator?

I always changed my coolant every 2 years and measure the strength in between.

Radiator cap may need changing.

These are the simpler things before looking at the head gasket!

[tonos]

It appears that I may have fixed the car.

Due to the symptoms, my first reaction was to replace the thermostat, but still not OK.

Made sure that there were no leaks, then got the car to running temperature. I then squeezed both of the large hoses at the radiator several times, making sure I didn't get too near the fans. Stopped car, then let water cool so that i avoided being scolded. I then located the white plastic radiator drain plug - it's just a plastic screw that can be removed by hand - then emptied the radiators contents. I was half expecting the coolant to be contaminated with rust, but it was surprisingly clean. I then ran water through the system a few times,giving it a flush, of sorts. Put things together, then filled up the radiator. Then started the car and got it to normal running conditions. Made sure the heater was turned up full, then topped up the coolant. Crossed my fingers, then went for a spin. Hey presto, it's fixed.

[tonos]

It appears that I may have fixed the car.

Due to the symptoms, my first reaction was to replace the thermostat, but still not OK.

Made sure that there were no leaks, then got the car to running temperature. I then squeezed both of the large hoses at the radiator several times, making sure I didn't get too near the fans. Stopped car, then let water cool so that i avoided being scolded. I then located the white plastic radiator drain plug - it's just a plastic screw that can be removed by hand - then emptied the radiators contents. I was half expecting the coolant to be contaminated with rust, but it was surprisingly clean. I then ran water through the system a few times,giving it a flush, of sorts. Put things together, then filled up the radiator. Then started the car and got it to normal running conditions. Made sure the heater was turned up full, then topped up the coolant. Crossed my fingers, then went for a spin. Hey presto, it's fixed.

[Konrad C]

Great work t.

These engines don't normally have coolant issues, especially if changed and purging of air locks. The water pump may give after time, but that's it.

Happy motoring.

Konrad

[Konrad C]

I was doing a bit of bicycle maintenance and noticed a drip under the car. Checked the drip with a paper towel and found it was coolant.

It turns out it was a hairline crack along the top plastic part of the radiator.

Now I am going to source a replacement radiator.

Should be a quick fix.

[Konrad C]

Changed the radiator. Cost £53 from Eurocarparts.

Removal is straight forward if the bolts are not rusted. After draining the coolant, disconnect the wiring to the fans and the cable holder to the O2 sensor and the upper hose the radiator.

The fans could not be removed due to rusted bolts at the bottom, so they came out with the old radiator. Then I could remove the bolts and swap the fans to the new radiator. To save time dealing with the bottom hose which is hard to access with the fans in situ, I disconnected from the hose from the engine. The hose is pushed towards the underside of the Battery tray, then under the air-con pipe. Then the whole unit can be lifted out of the engine bay.

I swapped the fans and the lower hose to the new fans and re-assembled. Job done.

I had noticed for a while that expansion bottle coolant level was dropping, but could not find the leak until the problem got worse. The hairline crack is hard to spot until it was big enough.

Tonos, you may have a similar problem so keep an eye on the coolant and watch for any drips.