3-Series (E21, E30)Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.
BimmerWerkz.com is the premier BMW Forum on the internet. Registered Users do not see the above ads.
On my m42 engine, my temp gauge bounces around in the hot and after just a few minutes it pegs to the hot side. The engine is not overheating. When it pegs hot, the engine runs poorly with bad hesitation until I give full gas then it picks up. It did this to a minor degree for a while, then the gauge returned to normal, the engine temp was fine, and it never ran poorly. Then after about 3 weeks, the problem came back only much worse. After running the car for 5 mins the gauge pegs to hot and the car hesitates from the moment I crank it up even dying on idle occasionally. The hesitation was perfectly concurrent with the gauge freaking out. I have replaced the single wire temp sender unit in the middle of the block but not the one near the front with 2 wires. I'd rather not replace any more good sensors to troubleshoot. What next?
I guess that means bleeding the cooling system. That seems to be a standard operation on these cars. I saw a thread once that had a couple of people describing the most thorough method of bleed an m42 cooling system but I cannot for the life of me find it again. Anyone link me to a guide for the procedure?
I have a 91 318i with the M42 engine. I've been where you've been. Before you start, buy a spare bleeder screw (part number 17 11 1 712 788), as I broke mine (the original that came with the car) trying to loosen it.
With the engine cold, open up the radiator cap above the expansion tank and ensure your reservoir tank is filled and kept filled with coolant mix. I'd also try to loosen the bleeder screw (the black plastic screw with the word Entloftung around it) and then barely tighten it.
Set the heater control to warm, start your engine and bring it to operating temperature. While the engine is warming up, gently loosen your bleeder screw. You should get some bubbles and hissing as the air and coolant escapes through the bleeder screw. When only coolant escapes through the bleeder screw, then tighten the bleeder screw to 4.5 - 7 ft lbs (Chilton manual).
Shut off the engine, replace any coolant you lost, then replace the radiator cap.
When the engine is cool, your coolant level in the expansion tank should be near the Cool mark.
I did this as part of a coolant change, and the temp gauge has stayed left of center for the most part, and with a lot less needle jitter.
Oh, one thing in regard to my original problem. My temp gauge problem was also associated with a progressing idle/rough running problem. It was my intake gasket all along. Why a bad intake gasket causing me huge idle - hesitation problems would cause my temp gauge to bounce and peg with 2 mins of warming up is totally beyond me. If anyone can answer the riddle please sound off because I am baffled by that.
Oh, one thing in regard to my original problem. My temp gauge problem was also associated with a progressing idle/rough running problem. It was my intake gasket all along. Why a bad intake gasket causing me huge idle - hesitation problems would cause my temp gauge to bounce and peg with 2 mins of warming up is totally beyond me. If anyone can answer the riddle please sound off because I am baffled by that.
I'm not sure they're connected. It might be coincidental.
Had the intake gasket issue, but on a 1990 325iC. The temp gauge on the convertible has not been an issue in the four years I've taken care of it, even during the time when the motor was hissing like a snake.
Times I've seen red from the temp gauge (other than coolant loss from a failed hose): failure to bleed the system, a failed water pump (both on the 91), thermostat stuck closed (Volvo 850).
I like my temp gauge to be rock steady. Toward that end, recently I swapped the dual temp (91/99 C) sender, and put in a replacement fan clutch. Went on a nice highway run at speeds from 60 to 85, and saw the temp gauge be anywhere from the 1/4 to 5/8 mark, but mostly a little left of center.
I know some other solutions involve getting into the instrument cluster to cure a bouncing temp switch, but I like bleeding the system as a first step.
I'm not sure they're connected. It might be coincidental.
They were absolutely directly related to each other. After fixing my intake manifold my temp gauge calmed down 99%. I get a little flicker once a week or so but a single tap on my instrument cluster glass returns the needle to its proper position. When I had a leaky intake gasket my needle would bounce erratically then peg on full red within 2 mins of startup. All's well that ends well, but I am very curious what the connection between a vacuum leak and my temp gauge is.
I like my temp gauge to be rock steady. Toward that end, recently I swapped the dual temp (91/99 C) sender, and put in a replacement fan clutch. Went on a nice highway run at speeds from 60 to 85, and saw the temp gauge be anywhere from the 1/4 to 5/8 mark, but mostly a little left of center.
I know some other solutions involve getting into the instrument cluster to cure a bouncing temp switch, but I like bleeding the system as a first step.
I recently had to drop in about half-a-gallon of 50-50 mix. Some of that was bleeding the system, but most of it was to replace coolant lost through a slow leak out what I suspect to be the integrated coolant expansion tank (seeing the drips on the driver side of the splash guard). The temp needle has returned to its customary position between the quarter and half-way mark, but I can see what my next repair task will be.
On my m42 engine, my temp gauge bounces around in the hot and after just a few minutes it pegs to the hot side. The engine is not overheating. When it pegs hot, the engine runs poorly with bad hesitation until I give full gas then it picks up. It did this to a minor degree for a while, then the gauge returned to normal, the engine temp was fine, and it never ran poorly. Then after about 3 weeks, the problem came back only much worse. After running the car for 5 mins the gauge pegs to hot and the car hesitates from the moment I crank it up even dying on idle occasionally. The hesitation was perfectly concurrent with the gauge freaking out. I have replaced the single wire temp sender unit in the middle of the block but not the one near the front with 2 wires. I'd rather not replace any more good sensors to troubleshoot. What next?
The front sensor "reports" temperature to the ECU, so you can imagine the potential for mischief if the computer is getting unstable or erroneous input. On a different car (Volvo), the engine temp gauge pegged full cold, ran poorly, and eventually wouldn't start. That was cured by changing out the ECU (I wish it was just a temp sensor).
Other places to look or things I've replaced over the years to deal with M42 driveability issues:
Reconnecting a loose vacuum hose on the bottom of the rubber air intake boot
Main DME relay
Fuel pump relay
Fuel pump and getting its main electrical connector redone
Stayed ahead of the curve by regularly changing spark plugs, air, and fuel filters.
Fuel pressure regulator (not in my personal experience, but have read about it as an area to look at).
A single gray/white connector (under a black plastic cover at the back of the engine -- also covers the relays listed above) that should *not* be connnected on US spec cars with catalytic converters. Look for the sports.racer entry on the first page of the link below.
Engine theory states that leaking inlet gasket = excess air into combustionchamber = lean side of stoichiometric combustion. Most would thing excess air = cool burn wheras it really = hot burn. Therefore a leaking inlet manifold results in 'hot burn' = higher temperature = temp guage reading high.
The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.
AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.
This has worked for me 
I hope this doesn't sound like grasping at straws 
Linear Mode
