Derin's Overheating Problem

[rodpaine]

Originally posted in the Eye Candy, moved here the only way I know how.

Darin wrote:

Sorry but my first contribution is to ask if anyone can help me shed some light on a problem that has really got me stumped!

As follows:

On the E28 528i when driving at normal/ sort of cruising speeds the temperature gauge sits pretty central just as it does when idling.

However, after faster driving and then slowing down again to low speed the temperature gauge climbs. It can go up to about 3/4 but has never gone into the red. If I then accelerate hard again it'll drop down again quite quickly (i.e even with 100 yards!)...It can even go below the central position! Slow down again needle goes up...then eventually will settle centrally again and stay there if you come to a stop and idle.

So far I've done or changed the following:

1) New thermostat

2) Flushed the cooling system at least twice

3) Changed viscous coupling 4 (four!) times...2 new, 2 used (I know for sure the one in there now is good!)

4) New radiator and water pump fitted yesterday

The car doesn't seem to lose any coolant and there doesn't appear to be an signs of oil in the water or vice versa.

Mechanic today suggested it might just be a fault with the instruments ... some kind of voltage something or other? I don't understand much about electrics (I didn't have the car with me whilst I was talking to him). He suggested maybe trying the instruments from another car...but I don't have easy access to that.

Is that really a possibility? Or are there any other suggestions?

Any suggestions gratefully received as I'm running out of patience (and money!)

Many thanks!

Have you tried the Bentley check of shorting the temp gauge sensor wire to ground and seeing what the temp gauge does? Can you borrow an infrared temp sensor to see what the temp actually is at the thermostat housing? I assume you did bleed the system fully, after all the changes and you don't still have some air in the system?
-Rod

[Derin]

Rod,

I'm gonna try both your suggestions.

My mechanic has an infra red temp sensor. He demonstrated it on my person the other day ( I didn't have the E28 with me that day...was there getting some things sorted out on my E32). He pointed the thing at my legs...17C...at my heart ...23C....Hey, I'm a cool guy! LOL!!!

Anyway, I see if he'll left me borrow it. Also is there anywhere on here that describes the best way to bleed air out of the cooling system? I'm not sure if I'm using the best technique.

Thanks again.

[rodpaine]

Snip... Also is there anywhere on here that describes the best way to bleed air out of the cooling system? I'm not sure if I'm using the best technique.

You simply want to make sure that you have a continous stream of coolant coming out of the bleed port on the thermostat housing, with the engine running and the heater set at maximum heat. If it is sputtering, then you still have some air in the system. Also, note the level of coolant in your expansion tank when you shut the engine off for the day and check it again the next day, adding coolant to bring it back up to its normal cold level. It will draw down as it cools overnight, until it is truly full. Keep an eye on this level for a few days of operation to make sure you don't have a leak somewhere, since you changed so many of the cooling system components.
-Rod

[E12driver]

Rod, did you ever have your welder friend attach an aluminum hose nipple to the thermostat housing bleed hole area, like you showed me, to allow attachment of a rubber hose so that bleeding coolant could be directed into a catch can and not run all over the fan belts and block? If so, can you have him make me one?
Carl

[Shawn D.]

Carl,

Your 528i is an M30, and on my 535i, I've never had to bleed the system while running. As long as you're on a flat surface (or facing uphill), it should bleed fine.

In any case, you don't really need to go to the trouble of welding if you're really intent on adding a tube -- you could tap and use a petcock.

-Shawn

[Derin]

Snip... Also is there anywhere on here that describes the best way to bleed air out of the cooling system? I'm not sure if I'm using the best technique.

You simply want to make sure that you have a continous stream of coolant coming out of the bleed port on the thermostat housing, with the engine running and the heater set at maximum heat. If it is sputtering, then you still have some air in the system. Also, note the level of coolant in your expansion tank when you shut the engine off for the day and check it again the next day, adding coolant to bring it back up to its normal cold level. It will draw down as it cools overnight, until it is truly full. Keep an eye on this level for a few days of operation to make sure you don't have a leak somewhere, since you changed so many of the cooling system components.
-Rod

Ok...I'll try it again this weekend (work committments permitting). I'll do it and leave ot overnight and see what the level does in the expansion tank as you suggest.

When you open the bleed nipple do you tend to just open a very small amount so only a little coolant escapes at a time? And should there be absolutely no air bubbles coming out at all once the job's done correctly? Maybe I'm making a big deal of it...but how long do you stand there watching to see if it's all circulated thorough? I mean sometimes I've thought:
" Oh that's it...it looks ok now....I'll just tighten the screw down now and then suddenly another air-bubble!"

[LA]

The pattern described is normal and unless the temp reaches the boiling point of your coolant mixture & you lose coolant then I don't think there is a problem.

[rodpaine]

Snip... did you ever have your welder friend attach an aluminum hose nipple to the thermostat housing bleed hole area...

Carl,
Shawn is correct, what I showed you was for my M20, not for an M30. And no, never did get anything welded up, still on the list though.
-Rod

[rodpaine]

Snip...When you open the bleed nipple do you tend to just open a very small amount so only a little coolant escapes at a time? And should there be absolutely no air bubbles coming out at all once the job's done correctly?

Derin,
Correct on both counts. Shawn's suggestion to be facing up hill a bit also helps. I'd be interested in what the IR Temp gauge says, versus what your temp gauge shows, which is typically this...
-Rod

[Derin]

Thanks LA,
I've also read that somewhere else...and I'd be inclined (and hopeful!) that there isn't a serious problem. The trouble is that now I'm trying to sell the car buyers may not share our faith?

Also, on my E32 (also with an M30 engine) the needle never waivers from dead centre.

Well, I tried rebleeding the system thsi morning...didn't seem like there was any air in there...got spattered again with coolant flying off the fan

I then took it for a short drive...samething again! I'm now really begining to favour the 'electrical thing'. When the needle has crept up if you then accelerate hard with 3 seconds (!) the needle has started coming down! It doesn't 'flick down' but you can easily visibly see it dropping. Accelerate hard again (i.e high revs) once the needle has got to the central position again...and it'll drop below the centre mark appreciably.

Seeing that helpful pic you put up, Rod of what the temperature differentials are supposed to be at the various positions on the scale I don't think it would be possible for the actually coolant temp to drop as fast as I'm seeing it?

I'll have to start seeing if I can at least borrow an instrument cluster to explore this theory as well.

[rodpaine]

Derin,
With such rapid gauge changes, I'd certainly look at the temp sensor for the gauge and its wiring, including its grounds. The IR temp meter would also show this up quickly, if it's the issue. In fact, I've found that many operating issues with friends E28s have been associated with old temp sensors, often overlooked. The temp gauge is just one of those sensors.
-Rod

[Derin]

Yes Rod,
I think and am hopefully we might be zero-ing in on the culprit(s). I 've been scan the archives here and also on your site.

Not only do I have this temperature gauge issue the car also idles badly when cold (lumpy and slow) which then settles and the revs pick up once warm.

I'm going to check these things this afternoon.

I'm just wondering if these sensors are the same as the M30 engine on my E32 735i...if they are may be I'll just try taking the ones off the E32 and fitting as a test.

I'll keep you posted on what transpires.

Cheers

[rodpaine]

Snip... I'm just wondering if these sensors are the same as the M30 engine on my E32 735i...if they are may be I'll just try taking the ones off the E32 and fitting as a test.

Derin,
No, I don't think they are the same, I've sent you E-mail with links to check this out based on the build date of your 528i and 735i.
-Rod

[Derin]

Just checked...unfortunately the sensor appear to be different on my E32. Nevertheless, I checked and cleaned all the contacts to them...sadly no better.

I think I'll just to it to my BMW specialist garage and him sort it out.

[Mark 88/M5 Houston]

Derin wrote:

I think I'll just to it to my BMW specialist garage and him sort it out.

I know your level of frustration is fairly high at this point . I would recommend that you source the sensors and sealing rings/gaskets and put them in before you give it to the mechanic. For the money invested, you will be well ahead if they fix the gauge and cold running issues.

[Derin]

Thanks Mark

You're right! Frustration levels got so high last night I started taking things apart myself whereupon I discovered other problems whilst in the process of accessing the ICV for cleaning.

Several of the vacuum hoses were very hard and had splits in them. Indeed, I'm amazed the car was even running as well as it was!

I'm not the world's best or patient of home-mechanics and now I fear I've dug a really big hole for myself. So frustration levels could go so high over the next few days they could easily transform into despair as bank account levels go down!

As of "so far", I now have all the injectors out (except the cold start injector which I'll attempt to remove today).

I'll have to order the new hoses, injector O-rings etc during the coming week from my local BMW-stealer. My 528i has three sensors all in a row on the big water casing near the thermostat. What do they all do? Should I get all three? (well, I guess I know the answer to that really).

Thanks and I'll keep you all updated.

[Rich Euro M5]

My 528i has three sensors all in a row on the big water casing near the thermostat. What do they all do? Should I get all three? (well, I guess I know the answer to that really).

The three sensors are:

Coolant Temperature sensor, the plastic part of the connector will look like an injector connector and the connector on the sensor is typically blue. This one is responsible for telling the Motronic / L-Jet ECU what the coolant temp is. This is a major player in setting your A/F ratio.

The smallest sensor with the spade lug and a couple of wires on spade connectors is the Temp Gauge Sender. It's only purpose is to provide the variable resistance which reflects coolant temp via the dash gauge. If you disconnect the wire and ground it with the ignition on, you should see a full hot gauge deflection.

The largest of the three sensors is the Termal Time Switch and is only used for cold start enrichment. It's pulled in by the starter solenoid during starting and energizes the Cold Start Valve "CSV"when the coolant temp is below the value stamped on the side of the sensor. When the coolant temp is above the value, the CSV will not engergize. It will also have a time value, typically 8 seconds stamped into the side of the body. This is the maximum time the CSV will be energized when the coolant is cold.

FWIW: I just read your original post which Rodpaine had put in a quote box at the top of this thread. IMO, your temp gauge is functioning normally. You cannot compare the movements of the E28 temp gauge to later BMWs. The temp gauge in an E28 is indicating what is actually happening to the coolant temperature. Later model BMWs and most other late model autos have what's known as buffered gauges. In the case of BMWs if the temperature stays with a nominal operating range, the temp gauge will always indicate 12 O'clock. Only when the temperature moves out of the acceptable range will you see something other than 12 O'clock on a buffered gauge, which usually occurs just seconds before you overheat.

Before you start throwing more money/ parts at the problem. Find and correct all your vacuum leaks. Vacuum leaks cause a lean A/F mixture which the O2 sensor (if equipped) cannot compensate. This is the adaptaion part of Motronic. If you have L-jet, you probably don't have this, unless you have an O2 sensor. Lean A/F ratios will lead to higher engine temperatures. Verify the condition of the bellows between the AFM and the Throttle Body. It should be soft and flexible, if it's rock hard replace it. Also replace the other hoses in around the ICV and throttle body. Hard hoses don't seal and lead to vacuum leaks. Also check the condition of the Oil Fill cap gasket and the oil dip stick seals correctly.

Once you have the vacuum leaks under control, then start looking at other possible faults.

Please tell us the last 7 digits of your VIN. This will allow us to decode model year, which will indicate which water pump pulley you have. Early E28s have a larger diameter water pump pulley, this slows down the speed of the pump and can lead to higher coolant temps. Later model year E28s have a small diameter pulley which increases the speed of the water pump, thereby increasing coolant flow. This is most noticeable at idle.

HTH,

Rich

[LA]

If the thermal-time sensor is bad the car will not run at all in my experience. I don't believe the A/F ratio sender would cause the temp needle to jump. I hope you replaced the temp sensor that sends the signal to the gage as the first shot at the problem, if not then I would spend that ten bucks.

Take the vacuum line to a chain parts store and buy lengths of the correct diameter hose, you don't need the stealer for those!

If the problem is that your gage needle is jumping like a tick of the second hand on a clock from time to time, then it's an electrical poltergeist as has been mentioned. The engine temp simply can not change as a step function. I've seen this 'tick' in a few temp gages and as I said before, unless you are losing coolant I don't think you have a problem.

Frustration levels go exponential trying to solve a non-existent problem Can you say OCD?

[Derin]

Many thanks to both Rich and LA for those great pieces of advice.

Firstly, here are the last 7-digits of my chassis number:

9388054

However, I have just fitted a brand new water pump. It's made by a company called KW (IIRC?). So I'm not sure if that helps determine which type it is?

I'm now beginning to think I may have been chasing a wild-goose all because of the demands of a 'potential' buyer wanting to see the gauge permanently sitting in the middle...who in any event may have turned out to be a scammer as he wanted to take the car without cleared funds having been received!

That's really interesting and excellent advice about the 'unbuffered' and 'buffered' temperature gauges. Coupled with the photo Rod posted earlier in this thread showing actually how little in terms of degrees of temperature causes quite wide deflections of the needle is really beginning to make me think I have been on a wild-goose chase especially as the needle has never gone into the red!

The temp gauge doesn't 'flick' i.e in a really quick fashion which as said would make it appear overtly electrical...It's more a steady but visible movement over a few seconds when it's on it's way down if suddenly accelerating fast...rising much more slowly on slowing down....and then settling slowly again to a more central position after a period. There now seem to several people saying this should be regarded as normal and the above explanation of why is really helpful....I'm very grateful. I wish I'd known this myself before I went to the expenses even on the radiator and water pump....Even my mechanic gave me my old radiator back saying: "You may as well keep that because I don't think there's anything wrong with that at all!" An exercise which alone cost me a further equivalent of circa US $800!

As a final check on this front I'll do as Rod suggested and borrow my mechnic's infrared thermometer and point that at the thermostat housing. Even the mechanic said if we do that and it isn't over-heating you don't have a problem!

Now that I have taken it all to pieces I'll still replace the hoses in and around the ICV and the throttle body as they're the ones that were hard and brittle....on the sclae of my costs that should be too bad. Fortunately, I already a brand new one of the large bellows type connection between the AFM and the Throttle body in my garage...it's just the smaller ones I'll get sorted. I'll also get the sensor to gauge if it's such a cheap part.

I'm very grateful for all this sound advice. Thank you!

BTW...What is "OCD"?

BTW 2 Why does the text always mis-spell G A U G E in that funny way when I try to write it here? Watch.... gauge! What is it with me and g a u g e s at the moment?!

See! Now it didn't do it!

[LA]

1. OCD - obsessive compulsive disorder, meant as a joke but may have been in bad taste. It is the premise of the TV show Monk. It can be big problems because people with it can get really carried away with things, sometimes things like alcohol and drugs. If managed however it can actually be a positive thing. This is speaking from personal experience BTW.

2. I thought people spelled it in that off-the-wall manner because of the gauge vs. gage debate. Both are good words and do mean different things but I not going to enter that debate.

[LA]

Wow! It just did it to me. I typed G A U G E (with out spaces) and when it showed up in the post it was 'gooahj.'

[Derin]

Oh! Given that I'm actually a doctor (though not a psychiatrist!) I should have realised what OCD was...i just didn't recognise it here (sorry for my correct...Ooops! I meant English... way of spelling recognise...No, let's not enter that debate either )

One of the worst/most annoying OCD phenomenon I've seen is a lady who couldn't go to bed until the last light switch she turned off at night had made that certain, right sounding 'click'!

My temp needle OCD is liveable with compared with that huh?....Well, maybe not!

[LA]

Just depends on what is important to you ... getting 'just the right clicking sound' is probably not expensive at all!

[Derin]

LOL!....True! In that sense she's far better off than me!

[Rich Euro M5]

Derin,

I checked the PN for the water pump pulley based on your VIN and your E28 has the older large diameter pulley which is 144mm in diameter.

After 9/84 the water pump pulley was reduced in diameter to 130mm which results in the water pump spinning faster. A side benefit is it lessens the chance of the lower radiator hose from getting cut by the belt. The PN for the 130mm pulley is 11 51 1 706 781 and also requires a new fan belt (12.5 x 1040) 11 22 1 706 788.

FWIW: Your E28 has a September build date, the ETK throws up a information message about these cars.

Rich