Top 20 1990 Mercedes-Benz 300 Diesel Questions & Answers

Requires special tools. Take to pro.

Freon goes in the ac system and is adjusted to an operating system pressure for the gas in use. If you need to add gas then you have a leak so it would be a good idea to visit an accredited ac specialist shop to find and fix the leak and have the correct amount of gas added.

1 gal = 3.785 L

check oile level in gear box

Assuming its an E-Class. have a look at the inside of the door where the lock catch is, there should be a little bung over a hole. remove the one on the same hight as your door handle. under it you can see a hex key bolt. Undo this bolt and the 'key lock' can be withdrawn outwards seperate from the door handle.

it could be defend on what place you are in this world. there are recommended oil for a particular place whether you use synthetic, semi-synthetis or a mineral(non-synthetic) oil.better to look the original owner's manual what oil is recommended onyour place.and suggest the ff.20-40 or 20-50 for hotter climat w/o freezing temperature5-30 to 5-20 w/ hot/cold climate

If it is from wear in the lock cylinders or dirt, get someone who fenced epee or foil ( I kid you not) the motion of "picking up the blade" and counter is what I use for such situations of a stubborn lock with great success. it is that subtle wrist motion that makes the difference.

Mercedes issued a bulletin about 15 years ago about the Temperature Gauge...let's see if I can remember what they said......

''As long as the coolant is not ejected from the reservoir bottle , the gauge being in the RED zone is not cause for alarm as long as when resuming driving on the highway the temperature returns to normal.''

In other words, they expect the temperature to rise when you come into traffic or a drive thro ....but as long as no coolant is escaping, this is normal.

However, if coolant always runs at above 190F you have a problem. This may be because the aux' electric fan/s is/are not operational or the thermostat is not opening fully.

If the system is full and low coolant light is not on and you don't need to fill up the coolant often, then those points apply.

When it gets to 120 next time, get out and leave engine running and open the hood/bonnet. The electric fan/s should be running. If not you need to check for power at the fan/s or from the Temp' Sender on the cylinder head .

On these older Mercedes the fan will come on if you bump the fan boss with your hand or a rubber mallet.

One more test: With engine cold but running for about 2 minutes... grasp the top radiator hose...if it is firm you have a head gasket failure or cracked head.

Wow what you towing it with a scania truck ??? if a manualo gearbox then no problem but a auto then the answer is no ,also its illegal to tow with a A frame in europe so its either the front up or a trailor here out local guardia civil would have a field day here in spain with something like this thats for sure

Try or (have your mechanic) remove oil pressure switch and clean. They gum up and it's a safety feature that when car is in accident and/or roll over, when oil pressure drops (eng quits) power to fuel pump shuts off. Sticking oil pressure switch is common on Benz Diesels

All I can think of is:

1. Are the battery terminals clean? (even then it should probably still turn)
2. Are the connections clean/fallen off on the starter motor.

A quick way to test the battery is to switch on hgih beam and try and start the car. If they go very dim then the battery needs charging or one of the cells is gone.

Hope this helps.

Try checking the coolant in the radiator some times its got trapped air inside.

The heat in your car is generated by a heater; that heater runs with the coolant from the engine; to control the temperature on the pipe coming from the engine to the heater there's a valve.
In your case that valve is stuck open, probably because it was seized by deposits. All you have to do is to replace that valve. The same valve is used in all W126 models so you can find a replacement one very cheaply at a breakers yard.
The fan problem is electric so you must check all the connections, starting at the fan motor

thoroughly clean area around injectors,and then blow with compressed air so no bits will fall in the holes when injectors removed.loosen main injector pipe nut,remove return fuel line,dont lose copper washers,put special fuel bolts back in top of injector firm[by hand] undo holding down bolts evenly,undo fully injector pipe nut,.gently pry injector loose,and remove,making sure sealing washer at bottom also comes out..while I dont specifically know this particular engine,this guide applies to most diesel motors.I have rebuilt a 6v72 detroit motor,yrs ago.Assembly is reversal.may need to crank over to bleed diesel at injector,always use new sealing washers.

Injectors may need rebuilt. Relay on the drivers side fenderwell may need replaced. Go to benzworld.org for more specific help troubleshooting.

check the blower fuse? check for voltage at the switch (requires removing heater / ac controls from dash on most vehicles.)

Locate the tensioner pulley; as you face the engine it is located two in from the right and midway down. It can be identified as a the smooth wheel with the inside ribs of the V (fan) belt facing outwards. In the middle there is splined (torx) nut and a black collar at its base against the wheel. An 8mm socket should fit on this splined shaft pretty well if you don't have the correct size of torx socket. Set the socket wrench at the 3 O'clock position and lift it, as if to undo the torx shaft. With a bit of effort the tension pulley can be lifted against its spring and in the process the belt will become slackened. Make a note of the pulleys and the direction of the belt traced around them. Lift the tensioner pulley and slip the belt forwards. Release the pulley and remove the old belt. Fit the new belt all the way around the pulleys, using your previous sketched layout of the belt th paas a guide, but leave the tensioner pulley until last. Re-engage your socket wrench on the splined shaft and as before lift the pulley against its tension spring. Slip the back of the belt over the tensioner pulley and release the pulley to put the belt back under tension. Note the order of pulleys on which you fit the belt is not critical. On some engine models the belt is first fitted to the tensioner and then fed around until a small pulley, such as for the alternator on the right hand side, is the only one not fitted. By creating a bit of slack by lifting the tensioner pulley it is possible to slip the v belt over this last pulley. Just as note sometimes the clatter from the diesel unit is not just the engine. The tensioner pulley has a damper unit fitted to it to stop it jumping around when the engine is running. The bushes for this damper can wear and the metal mounting collars can rattle loudly result. This can be checked whilst the engine is running by locating the damper and pressing a long handled screw-driver to the end of the damper. If applying pressure to the damper creates a change in engine noise then it is likely that the bushes are worn. If that is the case it can be replaced, I have tried fixing the bushes but nothing has worked for me. I mention all this as this is a good time to address this when replacing the the v belt. The plastic collar at the base of the splined shaft on the tensioner pulley can be prised off and beneath it there is a 15mm tensioner pulley retaining nut; obviously the belt needs to be off first. Removing the tensioner pulley allows access to the 13mm damper mounting bolt.

Yes if a proper tow bar is afixed. Bumper may have to be notched to fold out of the way to drive the car when not being towed. Make sure to have car in neutral.

You sure? Hard to reroute hoses on a MB.. Most likely culprits in this order, thermostat, radiator cap seal/spring, fan/fans not coming on, viscous fan clutch(mechanical) bad, switch on a/c that reads charge/low a/c charge not turning fan on when interior cooling on.

It seems like the radio still keeps a process in memory even after disconnecting the battery, the only thing we can suggest is to take out the radio and remove the car connectors (for an hour or so), this should clear the memory, if the waiting screen is still there it mean that the radio is in some kind of extra security mode (happens when you enter wrong code several time), in this case the only source that can help you is the Mercedes dealership, go there and have the radio open ( so they don't charge you for opening the radio) and show them the problem, they must be able to clear the security mode by code tricks they have with themselves, hopefully they wont charge you for only giving you the new code. they'll find the new code according to your car's stereo serial number. Hope it helps and let me know if you need more advice/clarification. Best