Overheat Light

[Coffee&Doughnut 0]

The Overheat light on the sevice indicator near the rearview mirror has been lit for some time now, I am too embarrased to say how long. I have since flushed the coolent

system, replaced O2 sensor NGK one,thermostat and housing gasket.

What I would like to know is what variety of problems does the Overheat light indicate. And is it sometimes a matter of the car overheating perhaps on one occasion

then the light just remains on until it is reset?

[Grant 4]

It is not an engine overheat light, it is a cat convertor overheating light.

Do what I did, rip the bulb out.

Cheers

Grant

[Coffee&Doughnut 0]

So is that indicating an internal problem with the Cat, in that case maybe its not doing its job anyway?

What about ripping the Cat out is that a bad thing to do?

Actually the problem may have originally occurred last year, when I had an oil leak from the oil pressure switch it took a while for me to locate it. On long drives I had oil streaming down the pipes and across the cat, there it would just sizzle and burn.

[Grant 4]

Yup, get the cat removed, it is something I keep indenting to do, but have never got around to.

I suspect the sensor was stuffed for mine, as the light was on all of the time. To me it wasn't worth worrying about so I just removed the bulb.

Cheers

Grant

[Coffee&Doughnut 0]

I have read conflicting reports on wether removal of the Cat improves performonce or is detrimental. I have a free flow exhaust fitted what do you think the effects would be from a performance and emissions perspective?

[Carl 3]

I have read conflicting reports on wether removal of the Cat improves performonce or is detrimental. I have a free flow exhaust fitted what do you think the effects would be from a performance and emissions perspective?

My understanding is that NZ model cars (E30 and E34 for example) did not have cats installed as standard.

The cat is a carbon filter that gets clogged up over time so yours may simply have clogged up too much making it easy to overheat. You need to get rid of it. Removing it, however, will increase your carbon emissions.

I cut my cat out and replaced it with two resonators. The improvement was immediately noticeable.

E: Whether I pass or fail an emissions test will be something else.

Edited June 13, 2005 by ///Carl

[ScD 0]

From what I understand, the ECU reads the exhaust gasses after the cat to check your not killing the planet, and will make changes to the mixture and timing accordingly. If the ECU sees a reading way outside what it can correct for, it goes into limp mode.

I think you can get a small electronic box that fools the ECu into thinkning the cat is running perfectly, but I'm not sure.

[Grant 4]

From what I understand, the ECU reads the exhaust gasses after the cat to check your not killing the planet, and will make changes to the mixture and timing accordingly. If the ECU sees a reading way outside what it can correct for, it goes into limp mode.

I think you can get a small electronic box that fools the ECu into thinkning the cat is running perfectly, but I'm not sure.

I'm pretty sure that for an E30 that that is all wrong.

There is nothing after the cat that reads exhaust gasses.

Cheers

Grant

[Coffee&Doughnut 0]

If the catalytic converter is restricting exhaust flow due to some degree of blockage,

is that likely to make the car run rich or lean? I dont get smoke but I think I get higher than average carbon build in the tail pipe. I got 104 k on the clock and shorter than recomended maintenence intervals.

Carl, What is the difference between adding resonators or a couple of straight pipes?

[Carl 3]

Resonators are a straight through muffler but their sound muffling effectiveness varies. They can also help with the exhaust flow due to the expansion and contraction of the gasses but I don't know how and to what degree the effectiveness is.

[Coffee&Doughnut 0]

So straight through, same as free flow, such as remus,supersprint and so on?

I was wondering if you replace the Cat with some pipes or do you add some other tuned device prior to the muffler? In my case I got a remus.

Its just that I have seen if I remember correctly companies such as supersprint selling bits of exhaust pipe intended to replace the cat, if i am not mistaken. sorry I am little vague on the details.

[kiwi535 538]

its the oxygen sensor that varies the mixture to optimum,cause too richa mixture will kill a cat as does other things.Carl is right most NZ new Bmw were cat free until the mid nineties when we swapped to lead free petrol.Cains car NOT included.Wether or not you can use that info to your advantage is another story.When you ripped the cat out carl did you take the o2 sensor as well??

[Coffee&Doughnut 0]

So I presume there is a sensor connected to the Cat, if I were to determine if the sensor is working correctly then it would be fair to assume that the cat is stuffed.

I recently replaced a fried O2 sensor, I dont know how long it was not working but may have also contributed to the Cat overheating problem.

If I go forth and remove it at some point I dont know if it will effect rego, but those stainless steel centre pipe jobbies look good!

[Carl 3]

There was no O2 sensor on my cat, only the overheat sensor.

Besides, isn't the O2 sensor closer to the manifold, it doesn't have anything to do with the cat.

[Coffee&Doughnut 0]

What I was getting at was, that possibly over time a failed 02 sensor may cause the motor to run too rich contributing to the cat overheating and eventual failure.

The o2 sensor is on the downpipe just under the manifold but both the cat and 02 sensor are part of the emissions system..

I will check out the cat overheat sensor some time that will be interesting.

sorry it sounds like I am talking about an o2 sensor on the cat,in my previous post what I meant was, the heat sensor if there is one.

Edited June 14, 2005 by Coffee&Doughnut