Reply With QuoteI dont see how its bad unless the oil isn't warm enough. But I dont see how without any "load" it would be bad.
Major Contributor
Revving engine at neutral bad?
I have few cars that are not driven during winter seasons. I do start the car once every two weeks and run for 20 minutes. To warm up the engine faster to operating temperature, I would rev the engine up. Is revving the engine with no load on it bad for the engine? I was told that it is...?
Last edited by shogun; 06-25-2017 at 04:34 AM.
RICK
BMW 1995 525i (Alpine White)
2 Grand Master
I dont see how its bad unless the oil isn't warm enough. But I dont see how without any "load" it would be bad.
Major Contributor
Friend told me this after seeing me rev my engine. I don't go over 3k rpm and take it easy. Maybe another myth?
Originally Posted by BigKriss
RICK
BMW 1995 525i (Alpine White)
Super Moderator
copied
Caveats about the ZF automatic transmission!
The automatic transmission supplied in the 745I (edit: in the later e24 also) is the ZF 4HP-22 EH. This electronic slush box is a marvel of engineering for it’s time, and is a good match for the turbo motor. It has a flaw however that many owners have discovered the hard way, and I will detail it as best I can.
The problem is that after starting the engine, and selecting any gear, forward or reverse, the front clutch pack in the transmission is pressurized, and that pressure is not bled off when park or neutral are selected.
This will cause premature wear of the clutch plates if the car is idled for long periods after engaging a gear, and can actually burn the clutch plates out if the engine is revved for a period of time. This high rev condition is particularly scary when you consider the process many states require in the process of emissions testing, and also might cause much concern when having the Air Conditioning recharged.
There is a BMW service bulletin (posted in full below) on this phenomenon, to summarize it is permissible to operate the engine at speeds up to 2000 RPM for up to 90 seconds in Park, only if the engine has been shut down for at least 60 seconds, and only if no gear has been engaged after starting the engine. Once shifted into any gear, the clutches pressurize, and stay pressurized until the engine is shut off for a minute or so!
When I go for Emissions or A/C service, I explain the concern to the shop, most have heard of it and are glad to be reminded. I then stay with the car during any high idle operations just to be sure!
I and most other owners swear by synthetic transmission fluid, Mobil1, Amsoil, or Redline. There has been a concern expressed by Brett Anderson, that if the transmission has not been serviced regularly, that the conversion to synthetic could do more harm than good. Apparently a non serviced transmission can have lots of particles floating around and sticking to internal parts of the transmission, and when the change to synthetic loosens all these particles they become a hydraulic abrasive that can cause even worse damage to the transmission. So if you are unable to verify regular service on your trans, you might want to stick to just a good grade of ATF, and change it more frequently.
Many thanks to Jeff Moser, Chris Koch, Prakash Maggan, Brian Mihalka, and Alan Chung for sharing their collective wisdom of this problem.
BMW NA service bulletin # 24 01 91 (3196) dated June 1991
Subject: Transmission Failure during Exhaust Emission Testing
Models: All 1984, 1985, 1986 with 4-speed automatic transmission, 1987 635CSi, 735i, and L7.
Situation: There have been reported isolated cases of automatic transmissions failing during a High Idle Exhaust Emissions Check. The failures have resulted from a preconditioning procedure where the engine is held at high rpm for a prolonged period of time. The following applies to all states which have a High Idle Exhaust Emission Check.
As the internal transmission components experience normal wear over time, the possibility of transmission damage exists if the vehicle is operated for extended periods of time at high rpm in PARK or Neutral. Such operation does not constitute normal operating conditions. If, in exceptional cases such as A/C recharging, injector cleaning, charging system tests, or emissions testing, vehicle operation at high rpm in PARK or Neutral is required the following setup procedure must be performed prior to beginning such operations.
Solution: The emissions test must be conducted with the engine at operating temperature. If the engine is not at operating temperature prior to beginning the test, it is recommended that the vehicle be driven for a short period of time to bring the engine to operating temperature. DO NOT run the vehicle at high idle to achieve operating temperature.
Once the engine has reached operating temperature, the following pretest procedure must be performed BEFORE testing begins.
Setup Procedure for I/M Emission Test
1. Shift to PARK.
2. Turn engine OFF.
3. Wait at least 30 seconds.
4. Restart engine, LEAVE TRANSMISSION IN PARK. After the engine is started, DO NOT move the gear shift selector through the Forward or Reverse gears before or during the test sequence. DO NOT EXCEED 2000 RPM.
5. Begin emissions test procedure.
6. If the vehicle fails the emission test, some states allow for an extended pre-conditioning before the repeat test. In this case the following procedure should be adhered to.
Precondition Procedure
1. Shift into PARK and turn the engine OFF for 30 seconds.
2. Restart engine, LEAVE TRANSMISSION IN PARK.
3. Engine may be preconditioned at a maximum of 2000 RPM for up to 90 seconds, at which time the repeat test must begin.
If the above steps are not followed, serious transmission damage can result.
Note: Due to the unusual nature of the emissions check, this type of failure does not take place under normal operating conditions.
The rebuild with lots of pictures:
http://www.bimmer.info/~rickm/trannyrepairs.htm
If the above link won't open, try the archive from the WayBack Machine:
http://web.archive.org/web/200712290...nnyrepairs.htm
Rebuilding the ZF4HP22 in the UK (with mention of "Hanging" in first):
http://www.cowdery.org.uk/zf.php
Big, Big Time Poster
Great post, Shogun. I think the no-rev caveat also applies to the non-electronic 4hp22 automatic (no EH suffix), which is in the E30 325i models (but not the 325e) and some E36 3ers.
3 Grand Master
I wouldnt rev a motor to 3k to warm it up. Over 1k and I'm getting giddy.Friend told me this after seeing me rev my engine. I don't go over 3k rpm and take it easy. Maybe another myth?I'd no more rev its b....cks off in neutral than drive around in too high a gear. Why? Because I think it will cause wear and strain on the engine. I cant point to any studies or other evidence so I will just call it empathy
Major Contributor
Thanks Shogun for the info. I didn't know about the auto trans. But I don't really rev my E34 at neutral.Both cars that I do rev are manual trans. I've been told revving engine with no load is bad. I don't see why that would be...
RICK
BMW 1995 525i (Alpine White)
Major Contributor
Not sure what's worse... Taking longer to warm up by idle/low rpm or rev the engine slightly so it warms up faster?
I wouldnt rev a motor to 3k to warm it up. Over 1k and I'm getting giddy.
RICK
BMW 1995 525i (Alpine White)
Super Moderator
that is clearly mentioned in the owners manual, immediately start driving the car and do not wait till the engine gets warm in idle.
2 Grand Master
Erich, in your experience how much payy in the transmission pump is acceptable before it goes bad?
When I changed the engine in my car, there was 1-2mm of play on the input shaft. When I told a mechanic this (one that has done a few zf-4hp22 rebuilds), he said the pump was going bad and I should get it looked at. He said 1-2mm isn;t good, there should be no play. the gearbox has done 260,000kms without a rebuild yet.
.
PS. I'm in china now. There are no cars over 10 years old year. I've seen 1 e34 in shanghai and now e32s, one e39 and the rest are new BMWs. Plenty of longwheelbase cars in 3,5,7 series and x6's also.
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