Giving my 300SEL to my mom... need some things tended to... - PeachParts Mercedes-Benz Forum

86560SEL · #1 02-24-2010, 01:52 AM

Here is the deal. I am giving my mother my beloved 1988 300SEL, as I have purchased a 1991 Caprice Classic as my days off car.

The Mercedes has around 160K miles. Runs very good, no rust, nice paint, nice interior, etc. To my amazement, it still does not leak or burn any oil, but I think the front cover is leaking a little. No biggie - I dont have to add between changes. It runs fine and has never let me down, but I want it in tip-top order for her. She would not even put 4000-5000 miles per year on it if that. I am not much of a DIY'er either. We have a couple of good MB shops here... maybe they should see to some of this or would a good independent mechanic be OK?

There are some minor nagging things that I want info on to be the best way to handle.

1- fuel gauge - its jumpy and inaccurate. I was told removing the seat and then the sending unit and clean it would help... is this the only way? Is there some additive you can put in the tank to clean it? Myself, I would refill it every so often.

2- headlights get brighter occasionally... they fluctuate in intensity - sometimes its a constant and less noticeable flicker, but sometimes its an occasional much brighter intensity. I am thinking this is the voltage regulator needing replaced? Battery is good and never goes dead, even if I let it set for two weeks at a time, so I know its charging and there are no shorts.

3- coolant - need to get the green coolant out... new stuff in... I will do this myself.

4- odometer... stopped working 4000 miles ago in the summer when I reset the trip odometer which I was using to track my mileage because of the fuel gauge..

is this costly to replace?

5- transmission.... sometimes when shifting OUT of reverse it will clunk a bit... does this car have u-joints? Could that be the cause? What does the flex discs do?

6- tranny fluid... I have to add some about every 10 months (1/2 quart)... never see any drips under it though. Where is it going?

7- tires/alignment. It has some slack in the steering. Would an alignment take care of this? I want to replace the tires and get it aligned.

8- sometimes I get a fluctuation on acceleration and the idle is sometimes erratic. It will go up and down.... hmmm. ???

Thanks in advance for any additional information.

Here is a pic before the washing/waxing that I took on Sunday afternoon...

took this two weeks ago... DIRTY!

compu_85 · #2 02-24-2010, 09:40 AM

1- fuel gauge - its jumpy and inaccurate.
I would just pull the level sender and clean it mechanically. I believe you can access it by removing the first aid kit box.

2- headlights get brighter occasionally...
Get a good meter and see what the voltage is. If you don't see a change in battery voltage when the headlights change brightness it's probably a grounding problem. Do the dash lights brighten at the same time?

5- transmission.... sometimes when shifting OUT of reverse it will clunk a bit... does this car have u-joints? Could that be the cause? What does the flex discs do?
There are no U joints, the flex disks take their place. If they are original, replace them.

6- tranny fluid... I have to add some about every 10 months (1/2 quart)... never see any drips under it though. Where is it going?
I would find the vacuum line going from the transmission to the intake, and see if it is wet with transmission oil.

7- tires/alignment. It has some slack in the steering. Would an alignment take care of this? I want to replace the tires and get it aligned.
An alignment will not fix this, but when you take it in the tech may find the cause, which is probably a combination of worn bushings on the steering linkages and a worn steering box.

8- sometimes I get a fluctuation on acceleration and the idle is sometimes erratic. It will go up and down.... hmmm. ???
Welcome to owning a car with CIS

Look for vacuum leaks. If the vacuum lines are original some are probably due for replacement anyway. The hard plastic lines tend to last a very long time, but the little rubber elbows that connect them can start to leak.

-Jason

Rob Pruijt · #3 02-24-2010, 12:41 PM

If your headlights get brighter, you voltage regulator is going bad. Replace it, if the voltage gets to high your battery gets overcharged. This ruins you battery and can be dangerous to.

It may even solve the erratic reading from you meters.
5 minutes job and not very expensive. I would advice to get a genuine Bosch regulator, cheap ones often burn out quickly.

Wait until the engine is cooled down, very close to the exhaust!!!.

Rob

mak · #4 02-24-2010, 09:54 PM

At around this mileage and with age the fuel pump relay becomes erratic leading to engine shutoff's ,though the car restarts .A new relay is best ,but can be re-soldered .Same replacement holds good for the over voltage relay.

Fuses ; almost all the fuses become age eroded and lead to intermittent electrical faults including occasional flickering gauges and lights .Best replace all fuses from a fuse kit with brass fuses clean the tangs.Visual check fail to detect the bad fuses ,but does under a magnifying glass.

Idle control valve needs a good clean and rubber vacuum pipes replaced if hard.

ATF leakage is almost certainly due to a leaky vacuum modulator a low cost replacement.Shift quality will improve in smoothness.

Alternator replace the regulator or the unit itself if the commutator has a wear grove.The belt tensioner will likely go bad if you remove the alternator so its best to replace the alternator,belt ,tensioner in one go.
This will make the car reliable for a long time .I think of them as 20+ years consumables.

I hope this assists in your serviceing based on my experience with this very reliable model.
mak
300se W126

tinypanzer · #5 02-26-2010, 09:42 PM

The ATF leak can also be the cooler hoses, but still check the shift module. If the front timing cover isn't leaking too much then I'd leave it alone because it can be hit and miss doing a re-seal on that even if you do it by the book.

There are probably some hoses that could use replacing, the two that come to mind off the bat are the breather hose with two 45 degree bends in it on top of the motor, and the one under the manifolds that goes to among other things the cold-start injector.

I'd also go ahead and change the fluids that get neglected by non-mechanical owners such as brake, trans, and diffy fluid.

If you're feeling like money's no object, a new windshield is great for older drivers who tend to have less night vision. Wiper streaks and scratches make a huge difference on older eyes.

The idle air valve should be cleaned as previously stated, and can be easily tested with a 9v battery while removed.

I'm not sure about the '88, but on my '90 there is no fuel pump relay, it is integrated in to the fuel computer.

Sometimes a few doses of Techron can free up a sticky fuel level sender, but you may have to remove it.

The Odometer is a pretty easy gig, you need to order the 12 tooth gear from a place like odometergears.com. Outrageous to charge 30+ dollars for a tiny little plastic gear that doesn't run as smoothly as the original, but it does work and installing it ain't too bad if you're okay with working on small things. If I ever get around to opening my cluster on the 300SE again, I'll try a dab of grease on the gear to see if that quiets it down. You can actually hear it when it's cold.

I'd go ahead and replace ALL the fuses. You can get 'em cheap on the net and the old ones corrode and get flaky.

86560SEL · #6 03-07-2010, 01:02 AM

Thanks for all of the replies. I will definitely replace the voltage regulator.... looks easy enough... is that the thing on the back of the alternator that has two screws? I am assuming it pulls out and unplugs or something? I have never changed one before. I priced them and they are as cheap here (OEM) than an aftermarket one at local parts stores.

HOPEFULLY that may help the erratic idle. To answer someones question... yes, when the lights flicker... its ALL of them... headlights, dash lights, etc. They always seem to quickly pace and lightly fluctuate, but occasionally they will get these couple of times when they will get really bright for a moment, then go back down. The battery light is not on signaling any problems, but I guess that dont mean anything?

I will try the techron in the tank for the gauge and hope it works.

I may have a shop check out the gauge and odometer. The odometer stopped on me at 156K... that was back in August and I only drive the car once or twice a week at the most (about 40 miles per week), so I know its still under 160K.

The front cover leak is minor. I have not had to add any oil between changes. May need addressed in the future.

A/C was only cool last summer... probably out now. May have a small leak? I will check it, because she needs A/C, especially with my baby nephew.

Compressor dont look to be too old, but I dont know.

Need to clean the leaves from under the fuse box. Tried and tried to get what I can on several occasions... gee this is tough to do. What a poor design.

Engine is pretty clean for the most part...

As far as losing tranny fluid (about a 1/2 quart every 10 months), could it be from this hose? Strange, I never see any drips under the car.

Thanks for all of the replies.

Ferdman · #7 03-07-2010, 07:08 AM

Yes, 2 screws hold the voltage regulator in place. Once you remove the screws it pulls right out. No need to disconnect anything. Installation is the reverse order. Since the brushes on the new voltage regulator will be longer it will be slightly more difficult to install it, but still a simple DIY job.

The brushes on the old voltage regulator are probably worn down to nubs, so the battery doesn't recharge sufficiently.

Hirnbeiss · #8 03-07-2010, 07:52 AM

As to the tires & alignment, at your mileage it's a good bet that the tie rod ends are due for replacement - then get the alignment. Adjusting the front bearing play to spec is another thing you can DIY.

Mike Murrell · #9 03-07-2010, 08:11 PM

New brushes on OEM Bosch unit are 1/2" long. Gives you an idea how worn down the existing ones are.

Nice car.

86560SEL · #10 04-17-2010, 02:08 PM

Thanks Mike.

Just to update - new voltage regulator took care of everything... pulsing lights are gone as is the erratic idle!

JohnM. · #11 04-17-2010, 02:28 PM

The transmission cooler hose you pictured is wet with transmission fluid. Those are known to be a source of leaks and are cheap to replace. It may not be leaving drops when you park it, but while driving most likely.

Fixing the front cover is super easy. You just need a new rubber seal and some black RTV. And make sure you don't pinch the seal re-installing the front cover! I learned this tip from a good friend and have sealed more than a few engines this way with 0 leaks.