Engine cover tray - is it important?

[colin129]

One of the 964s I am looking at had its engine cover undertray removed for replacement of the clutch and flywheel and the seller says it has been left off and placed in storage. This, he says, assists with cooling and reduces the need for the fans to run so much. It also, he says, reduces the expense of having to drop the tray down each time (presumably for servicing?) and replace the nuts.

Is it normal to run the car without the undertray, presumably it is there for a reason? Maybe it is off to disguise the fact that the engine is getting too hot and the fans are always on?

The other thing is that it has not been rebuilt and has 122K on the clock. I think I read on here that Porsche GB rebuilt a lot of engines under warranty, but not all the owners took them up on the offer. Presumably I would be able to find out from them whether this had been done or not. Is the rebuild a once in a lifetime operation? Do ALL cars need this at some stage and say if it has been already been rebuit by Porsche in its early life, will it need it again at some stage.

I realise there are a lot of ifs and buts and it depends answers, but some indication would be helpful.

Otherwise, this could be the one!!

 

[Dave Wilkinson]

Colin,

There are many views on the undertray issue and many, many cars are run without it. There are a lot of pro and anti issues and it's pretty much an individual choice.

Obviously Porsche had a purpose in mind when they designed it and opinions tend to vary as to what those purposes might be. Many attest to noise reduction, some to air flow improvement and some to dirt protection of the engine. What Porsche probably DIDN'T forsee was the potential fire risk it poses - with an engine prone to oil leaks the undertray tends to collect the leaked oil and, with the heat of the exhaust so close, renders it a high fire risk. If the current owner of the car in question has the undertray in storage would it not be possible for him to get it for you - then you can make up your own mind.

Whilst the maintenance issue is valid it probably IS true that the engine runs cooler with the shield off rather than on. BTW, there are no fan issues relating to engine temperature - the only small exception is that the rear blower is designed to stay on after shut down IF, and ONLY IF, the engine temperature is above a set figure. The fans are otherwise to do with cabin heating rather than engine cooling. The big fan on the alternator is the only fan involved in cooling the engine - and that never stops.

Engine rebuilds is another emotive subject. Some early engines were, as you say, rebuilt by Porsche under warranty due to the perceived oil leak problem around the head/barrel joint. This is generally not the reason for engine (or even top end) rebuilds. Some owners will talk about their engine rebuilds like a badge of honour whereas others are proud to have seen 120,000 miles without such intervention (mine included). Justification for top end rebuilds should be lack or loss of compression, worn valve guides or similar issues. Oil leaks in themselves are difficult to justify as a reason although would obviously be sorted as a consequence. Bearing problems are relatively rare - although they do happen - and this would require a more complete rebuild.

The fact that an engine has been rebuilt would generally be seen as a bonus when a car is sold although it's existing condition would be a better yardstick.

Hope that helps.

Regards

Dave

 

[colin129]

Thanks - that is very helpful.

This engine rebuid thing being a 'badge of honour', is that a bit like my father's generation seeing their heart bypasses as a badge of honour?

i.e. It is not inevitable, but if you need one you need one and make sure its done properly?

 

[Dave Wilkinson]

ORIGINAL: colin129

Thanks - that is very helpful.

This engine rebuid thing being a 'badge of honour', is that a bit like my father's generation seeing their heart bypasses as a badge of honour?

i.e. It is not inevitable, but if you need one you need one and make sure its done properly?

You got it in one!!!

Dave

 

[Steve Brookes]

The good thing you're telling us here is that the undertray is available. So make sure you get it. I guess from what he's said that it's left off because of the pain of taking it on and off. I would agree that the first time you do it, it is, but when used to it, it's a 10 minute job to remove. Probably less for a mechanic with a lift.

Personally I wouldn't run my car without out because of the protection it offers against stones hitting the underside, road salt, etc. However I have to admit that the smaller cover for the gearbox is missing on mine and I hope I can find one, one day.

 

[chrism964]

Mileage is a thorny issue. Especially with the price of engine rebuilds (around £4000+ for the top end, although it is only a few hours extra work (I am told) to rebuild the whole lot in one go) being as it is. The specialist I go to says they would never recommend a top-end rebuild on its own as, in their opinion, if the top end needs rebuilding then they feel the additional cost of rebuilding the bottom end at the same time would outweigh the combined cost (and ball ache) of having the two done separately. They are also of the opinion that if the top end needs doing then the bottom end is most likely to benefit from renewal as well. I do not believe that they are just trying to squeeze extra money out of anyone.
However, maintenance and usage is more important than mileage (imho). Cars (especially Porsches) are designed to be driven and low mileage cars that aren't used regularly can be more of a problem than high mileage cars.
I have recently moved my place of work from 5 miles from home to 25 miles from home.
I have done 3000 miles in the last 3 months and I have noticed a considerable improvement in my cars performance (an fuel consumption) just from regular usage. It has just become a much better car to drive on the whole. The gear change is smoother, the brakes are better and it is just more of a joy to get into.
When I first got the car it had done 1500 miles since it's last MOT. The engine felt down on power compared to my previous car (Clio V6 230bhp) and the brakes were binding on all the time. There were also a number of clonks and bonks that would occur when first starting out. These only improved with use of the car and not with the very good service I got from the specialist I bought the car from.

I suppose what this ramble is supposed to be saying is try not to worry about mileage and whether the engine is rebuilt or not.
The most recent service history and the amount of usage is probably key.
I (and I always post this) would recommend that you get some one to do a proper inspection of the car before you part with your money. It may save you a packet in the long run. I didn't and have spent more than the price of an inspection correcting niggles that I could have made the vendor correct before I took ownership of the car.

HTH

 

[smallspeed]

ive removed my tray because one of the corners split and caused it to drop down.. ive not really noticed much noise increase although Im running a cat bypass and a cone filter so its hard to tell sometimes [] I was going to look out for a new engine undertray but instead have opted to manufacture my own from aluminium; its much lighter than the standard one and I intend adding a couple of removable pannels for servicing, drain holes for oil, etc... Just need to find the time to fit it

looking under the car it appears a lot of thought has been put into the standard undertrays; the whole underside of the vehicle is nice and flat with much of the usual lumps and bumps, tunnels, etc. removed or covered up; while I agree front engine cars see cabin noise benefits from engine undertrays (and it magically "stops the engine from leaking" in modern cars) Im of the opinion the undertray on the 964 is more of an aerodynamic benefit.. I also think the cooling thing is partly true however I believe the fan sucks air in from the rear of the car through the wing rather than blowing it out? if this is the case you are in effect creating more pressure for the fan to work against by removing the cover and forcing air from under the car backwards through the tinware and into the fan outlet, thus potentially reducing flow around the engine and creating static air pockets.. of course this hinges entirely on my assumption that the fan swallows rather than spits []

as for engine rebuilds; im chuffed mine has done nearly 300,000km without a rebuild, but slightly nervous too.. it feels nice and tight and pulls really well, but theres a part of me that wants to put it on the rollers and see what its putting out compared with std original or do a compression check for peace of mind.. I think you've hit the nail on the head too in that just because its had a re-build doesnt mean its any good; I went to look over a beetle engine for a mate a while back that had been rebuilt, and my opinion was stevie wonder and ray charles had collaborated on the project.. get info on work thats been done and then at least you know the history of the car, whether its been looked after or not, by whom, etc.. Also, while I know these cars were a technical marvel in their time, they are relatively simple and easy to work on by modern standards, and provided the person involved was reasonably competent (and you can get a good feel for this pretty quickly IMHO) then I dont see any reason to be scared off by a car thats had major servicing at a specialist and oil/filter changes, minor work, etc. done by the owner, and I would expect to see that on older/higher mileage/lower priced cars (like mine [] )

ben

 

[38F3E1]

You can run a 964 with or without the engine undertray in our climate.

Removing it has the advantage of letting the engine run a little cooler and letting oil drip on ground rather than collect in the tray. Keeping the tray on keeps the engine cleaner.

For the 933 they modified the tray to allow a larger gap between the engine and the tray in an admission that the 964 tray is a little to tight to the engine and does impare the cooling air flow from the fan a little. Personally I would remove it if you are doing trackdays.

There is no advantage to removing the transmission cover so this should always be fitted IMO.

Ian.