Pre-Cats Again (Groan)

Anonymous · April 5, 2006, 12:40

I hate to get into another pre-cat debate thread however..........I have been on the forums for a number of months now and have read most of the back history and opinion on the subject.

There is no doubt in my mind that the deteriation of the pre-cats can cause some real damage, typified by some the engine failures explained on this forum. However there are some niggles on my mind.

A number of failures seem to have occured at or around the time the pre-cats were taken out, which makes me nervous as I am looking to have the work done in a few months when my warranty begins to run down. I am not certain but it seems to paint a picture that removal of the cats has brought on oil loss or engine failure in some way.

A number of other serious (i.e. very expensive!) failures have also been caused for other reasons. This is usually manefested by a sudden loss of oil to the engine, and is not attributed to pre-cat degredation.

It seems to me that with pre-cat removal you are damned if you do and damned if you don't. The facts from the body of evidence of this forum is that removing my pre-cats won't nessecarily make the engine as reliable as it should be, and I still carry a significant risk of having a nice £3K suprise one day.

As much is the MR2 is a fine car, and I love it to bits I cant help but think I might be better off just chopping it in for something else when the warranty runs out. Something I dont want to do but constantly waiting for somehting to go as seriously wrong as this deadens the joy of ownership.

How many of you subscribe to my views, or feel I am not reading the situation right?

Tem · April 5, 2006, 13:11

Quote from: "ErikLobos"A number of failures seem to have occured at or around the time the pre-cats were taken out

The number of failures was already at three digits before anyone thought of removing the precats. s:? :? s:?

Many just don't seem to be worried about this before they get some symptoms and then they rush to take the precats out. I don't believe, nor can I even imagine, that removing the precats could cause this.

philster_d · April 5, 2006, 13:20

but when you remove a bottleneck from a system it typicaly moves on somewhere else ?

Anonymous · April 5, 2006, 16:04

I assume your referring to my situation when you say that an engine failed within days of removing the precats?

Having thought more into it, I'm beginning to believe this is pure coincidence as removing the precats couldnt cause such rapid oil starvation. As I think about it I had topped up my oil quite a few times since my last service.

I think there are 2 possible engine failures on the MR2 roadster, which can each be prevented:

1)Precat failure. Gut the precats.

2) Oil Starvation. Caused by overfilling an engine with oil, causing high oil pressure and too much pressure on piston rings. This subsequently causes poor compression and therefore oil usage. This oil usage causes the starvation and therefore big end bearing failure, amongst other things.

It would also be reasonable to assume that 2) could be a cause of 1) above, however this doesnt have to be true in every case.

Hope this helps,

Richie.

Anonymous · April 5, 2006, 16:06

AFAIK, no-one who has removed their pre-cats when they've been in perfect condition has ever suffered engine failure that is typical of the symptons directly related to what happens when the pre-cats give way. If that makes any sense.

Liz · April 5, 2006, 17:24

I think that only Richie [as above] has had an engine failure after removing the pre-cats and that is probably for the reasons that he has mentioned. Out of all of us that had removed them I would say that it is a tiny tiny percentage. We are not here preaching that you must gut your pre-cats, but enough people have had expensive failures to prove what can happen. Its really up to you.

philster_d · April 5, 2006, 17:46

Yes Liz, its personal choice, good point.

and on the subject of oil, i think thats how i blew up my mk2 na. the day before a long trip, i put some oil even tho it looked ok, I was trying to be clever.

The next day there was a catastrophic failure half way to manchester, apparently a seized oil pump, but at motorway speeds the engine was suddenly starved of oil. and even the non interference engine couldnt save me. s:cry: :cry: s:cry:

The recomendations i heard since, around imoc (and here) is dont even top it up to the top of the dipstick.

Phil

Anonymous · April 6, 2006, 09:29

Hi Guys

Roughly how many members have re-moved there pre-cats anyway?

Anonymous · April 6, 2006, 12:31

Thanks everyone for your thoughts it has helped me to make my mind up what I need to do.

Richie, I was refering to your case, although I can also recall a couple of other similar incidents. Your comments have helped. Thanks Ekona and Liz for your follow up comments.

All in all has been very helpful in crossing the T's and dotting the I's so far as my thoughts on this subject is concerned.

aaronjb · April 6, 2006, 12:38

Quote from: "predator_etal"Roughly how many members have re-moved there pre-cats anyway?

That's a good question - and not one I know the answer to s:)

s:)

I would venture a guess that it's probably a fair proportion, probably a higher proportion if you take Spyderchat into account as well..

But, bear in mind that we (the forum membership) make up a tiny proportion of total Spyder ownership, those are figures we'll never be able to account for in our failure rates.

Anonymous · April 6, 2006, 12:47

Quote from: "Richie"...overfilling an engine with oil, causing high oil pressure...

Can someone explain to me why a high oil level should result in high pressure?

Surely the oil pressure is created by the oil pump and that should have a relief valve in, or near, it which limits the pressure. How can a high oil level affect this mechanism?

The main problem I am aware of with an excessive oil level is that the crank journals hit the oil, causing unusual loading on the crank and excessive oil splash (and frothing?).

Anonymous · April 6, 2006, 12:55

Quote from: "ErikLobos"Thanks everyone for your thoughts it has helped me to make my mind up what I need to do.

Richie, I was refering to your case, although I can also recall a couple of other similar incidents. Your comments have helped. Thanks Ekona and Liz for your follow up comments.

All in all has been very helpful in crossing the T's and dotting the I's so far as my thoughts on this subject is concerned.

No Probs s:)

s:)