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Old 09-21-2004, 06:01 PM
SL Owner
Join Date: Sep 2004
Location: East Coast U.S.
Posts: 131
DIY Notes may help people: Radiator, Fan Clutch, Temp Sensors, Fuel Pump, Temp Gauge

This is a post summarizing my do-it-yourself notes from some recent work. I thought it might be helpful for anyone else on this list. As always, proceed with great care and if in-doubt, have a mechanic do the job. Some of this work is dangerous (e.g. the fuel pump) so proceed at your own risk... Since this system limits the size of the post, I have broken it into two posts, my next post will have the second part.

The tips on this list were invaluable. Even small details like "use a golf tee for a plug" were very helpful as transmission fluid started to drip from the open houses. Thanks to everyone for their input. I installed a new RadTech (looks to be Behr) radiator, fan clutch, and new temperature sensors in my car yesterday. In addition to what I did yesterday, I also have changed in the past few weeks the fuel pump myself (somewhat dangerous and some issues but not particularly difficult, be careful with that job), the thermostat, and your usual range of tune-up items (plugs, plug wires, rotor, cap) plus a few other small things. The car has never run better and the cost was probably 1/5th of what the local shops would have charged by the time they double to triple on the parts (and at least two mechanics in the area won't take parts if I buy them) and ungodly labor rates.

Here are a few notes from the work I did for each of these items:

0) Important Note- Instrument Cluster (Dashboard) Temperature Gauge

Do not rely on the guage only for troubleshooting a cooling system problem. I made use of an infrared thermometer and found it very useful. I was able to confirm that, for example, my temperature gauge was having a problem (jumping around, not accurate, pulsing with the turn-signal which may mean a ground issue). You can use an infrared temperature measurement device and shoot it at the water pump housing (you can paint some black paint on there to improve reflectivity). It provides useful information. Also, if you for example confirm your aux fan works by shorting the connector on the 212 switch connected to the thermostat housing to tround, and you change your 212 switch for $30 bucks and 15 minutes of your time, and your guage reads 110 but your fan doesn't go-on, you also have some confirmation that your temperature guage isn't working.

1) Radiator DIY Notes

First, whether or not you need to change the fan clutch, it is an easier job if you do both the radiator and fan clutch at the same time, at least on my 380 SL. It was very easy doing the fan clutch with the radiator and fan shround completely removed. Notes on the job:

1a) The RadTech radiator for the 1984 380 SL (and probably for other SL's?) appears to be 98% the same as the original radiator-- it's heavy metal and looks like the original. I'm very happy with it in terms of installation and apparent build quality. I was told it is made by Behr. For $309 it's nearly the price of getting an old one rebuilt. I'm keeping my old one anyway because I'd like to see over time how the radiator does but I'm very confident in it.

1b) After unclipping the radiator, note that the rubber mounts on the side of the radiator may stick. You may ask yourself if there is something else holding the radiator in. The answer is to use a screwdriver to gently unstick the rubber guides around the radiator (between the rubber guide and the body of the car only, don't do it near the radiator) and spray silicon down there. Next, get underneath the car and push-up on the radiator on each corner, alternating between the corners. Out it comes.

1c) HIT THOSE rusty transmission oil cooler hoses with PB Catalyst, Liquid Wrench, or if you're convinced it always works WD-40 before trying to loosen them. See next point.

1d) BUY the passenger-side transmission oil cooler hose, that thing has a right turn head on it (metal head) that fuses so much you'll never be able to turn it. Be prepared to change any hoses that you can see are easily changed. hat means you need to remove the hose back at the tube coming from underneath the engine. That's fine, it's pretty accessible (relatively speaking) from underneath the car, no biggie if you have a steady hand. But as noted on this list, you have to be VERY CAREFUL to support the hose tube as you unscrew it. If you damage the tube to which the transmission oil cooler bolts, my guess is you'll be a very unhappy camper (maybe the repair is easy but it didn't look like it). That means one wrench to hold the tube stable and another wrench to loosen the hose off of it. My radiator hoses had previously been changed, this just left my transmission oil cooler hoses, of which one I changed. Be prepared to change-out hoses, get them ahead of time if you plan to start and finish the job in one day.

1e) Remember to take the old fan shroud clips (at the bottom of the radiator) off of your old radiator and put them on the new radiator. Do this before you put the radiator back in the car, that's much easier than laying on your back and trying to get them in there.

2) Fan Clutch DIY Notes

2a) I believe the bolts on the fan clutch are 10 mm as I recall. These new GearWrench sprocket style wrenches (where you basically get a very thin ratchet wrench) are very useful for this job.

2b) Use a strap wrench, which you can buy at Sears or your local hardware store, to hold the water pump pulley in-place while you loosen the bolts. The large size one at sears with the rubber strap is really great for this job. The strap wrench also lets you easily turn the pulley so you can get each screw right up to the top so you can easily remove it.

2c) When you remove the old fan clutch and fan, you'll unbolt the fan and notice that they are STILL fused together. So how do you separate the fan from the fan clutch? You will notice there are some big holes that look like screw openings still left on the back of the fan clutch. If you poke a screwdriver through there and tap it with a hammer, out will come the fan from the fan clutch. I also hit it with PB Catalyst around the edges before hand, that probably helped.

2d) the order of assembly is fan clutch, then shroud, then radiator.

2e) remember how the fan goes on the fan clutch (orientation). It's pretty obvious when you think how it operates, but when it's hot and you are tired, you might reverse the fan which would really be aggravating.

3) Thermostat notes

3a) The thermostat on the SL is very accessible, right in the front of the engine, in front of the air cooler. I drained the coolant, took-off temperature sensor connectors (BE CAREFUL, see next notes), unbolted the screws, and changed the thermostat. Easy job. HOWEVER, note the following items

3b) On my car, just above the thermostat housing, is the idle control solenoid and connectors. On these cars, the connectors are very old and fragile. Wires pull-out from connectors. CAREFULLY remove any connectors you may hit when you are removing the thermostat such as this one. NEVER BEND OR TWIST a connector to get it out of the way, they are old an fragile. For most of these controls/sensors, if you break a connector, it's easier to go to the store and get a fitting you crimp back on there and onto the sensor/control than taking apart the Mercedes Benz connector and resoldering it. I did that (resoldered) but found it wasn't strong or reliable. New connectors from Radio Shack/the local auto store that you crimp on lock-in there and stay. If your car idles like a bat out of hell for example, you know you broke the idle control solenoid connectors.

3c) Similar to above, be very careful with the connectors for the car temperature sensor (for your dash) and the sensor/switch for your auxilliary fan. Those are both in the thermostat housing. When you unhock the connectors, BE VERY CAREFUL. If one breaks, see 3 b).

3d) The thermostat comes with a seal. That seal goes around the thermostat itself (the large outer circle of the thermostat where it sits in the thermostat housing). Don't be a dummy like I was and seat that gasket into the thermostat housing and sticking the thermostat on top of it. You'll spend 20 minutes trying to figure out why it leans. I know, that was stupid.

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Old 09-21-2004, 06:02 PM
SL Owner
Join Date: Sep 2004
Location: East Coast U.S.
Posts: 131
DIY Notes part 2: Fuel Pump and Temp Sensors

4) Fuel pump notes

4a) No matter how hard I tried on this job, fuel still poured out. That makes it a dangerous job when doing it from the ground without something to pump all the fuel from the tank ahead of time. You have to be careful doing this job if you choose to. For most people, I wouldn't recommend it.

4b) The mercedes benz manual tells you to pinch-off the fuel line coming from the tank. First-off, there's enough pressure coming from all of it that even if you pinch it off with a quality pincher (such as one that Sears sells), you are still going to get fuel out of there (also from fuel left in the system otherwise). Also, once you pinch-off that fuel line, you will probably crack it and cause a leak though I argue most of these cloth-lined 20+ year old hoses are ALREADY leaking-- mine had gas residue on it before I started the job but after I pinched it off, it was more evident. That means this job, for the DIY person, might also include replacing that fuel tank line. For most home mechanics, that will not be possible and so I took the car to my mechanic and for $150 he changed that hose. Expensive for a hose change but he can have it. I was glad to pay him to do that after I changed the fuel pump because I couldn't. He told me that most people, when changing the fuel line, DESTROY THEIR GAS TANK because the bolt from the fuel line hose gets fused and, despite using something to loosen the bolt, go to hard at it and strip the fuel line coupling in the tank. He told me he needed the car for 6 hours and would use PB Catalyst to loosen the bolt and take it out. But he scared me, indicating there were risks. Anyway, I had my car back at the end of the day.

4c) To remove the old fuel pump you need to get those old bolts out of there in the frame. You need PB Catalyst, liquid wrench, wd-40, whatever to loosen those bolts. Be careful not to strip the screw heads. Messing around with this will take you 45 minutes at least and some scraped knockles. You will then want to run-out to the hardware store and get new nuts and bolts, you will not want to re-use the old ones based on my experience.

4d) When removing the high pressure fuel fitting from the pump, you must SUPPORT the pump bolt/housing with another wrench so that the torque from removing the external hose does not destroy the old pump or the new pump when you do the reverse and install it. This is similar to the transmission oil cooler bolt example discussed earlier. Be CAREFUL, do not damage your new pump when tightening down this way, the pump cannot accept your torque.

4e) IMPORTANT, once you pull that old pump off the fuel line, fuel will come pouring out despire your best efforts. IMMEDIAGETELY GRAB THE NEW PUMP AND INSTALL IT ON THE FUEL LINE. The flow of gas will be stopped by the new pump and you will breath a sigh of relief.

4f) Carefully orient the new pump so that the positive and negative connectors (YOU SHOULD MAKE NOTE OF THESE WHEN YOU REMOVE THE OLD PUMP, THE ORIENTATION MATTERS ELSE THE PUMP WILL RUN IN REVERSE!) can easily plug into the new pump. Twist the pump around to get that before you tighten the hose clamp. Put the fuel pump back in the bracket housing, use your new bolts to mount it. Be sure to have the blue plastic stuff on the fuel pump between the pump and the brackets. This prevents corrosion. Tighten down the high pressure line as discussed above.

4g) Wipe the high pressure line with a rag. If it immediately becomes dark again it means you still have a leak there. In my case that meant tightening that hose down further. Once no leaks and everything looks good, proceed.

4h) Push the car without starting it away from the area where any fuel was spilled for safety. Start the car away from that to avoid any sparks. Again, for this kind of reason you really might have a mechanic do this job overall. Anyway, once away, start the car. Use a flashlight and look for leaks. See if the fuel line hose is damp, if so it needs to be replaced (see above). Give the car a drive if all looks good.

5) Temperature sensors

5a) On the theremostat housing are two sensors as mentioned above. One is for the car's dashboard thermostat and the other to turn on/off the aux fan. For about $30 mail order you can get both OEM sensors and simply replace them to remove any variables/guesses in terms of cooling system issues. It's a really easy job to remove them. Drain the radiator, see notes above about fragile connectors, and use the right size long socket wrench to turn it off of there and put a new one on. Easier than changing the oil in the car if you are careful.
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Old 09-22-2004, 07:46 AM
SL Owner
Join Date: Sep 2004
Location: East Coast U.S.
Posts: 131
Note the above notes are for a 1984 Mercedes 380SL (likely same/similer for all 107s)

I failed to mention the year/model of car in the orignal post. 1984 380 SL, probably same/similar for all 107 series cars
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Old 09-24-2004, 02:40 AM
Registered User
Join Date: Sep 2001
Location: Austin, TX
Posts: 563
A few more fuel notes:

Inspect the fuel hoses before you start the job. If they look dried out, buy new ones...all of them. One of them you have to buy by the meter, but you only need a few inches of it.

Use the hose between the elbow and the fuel accumulator to drain the tank. Remove the end on the fuel accumulator side and drop it in a gas can. Make sure you have enough storage for the gas. Hopefully you won't have a full tank.

I got my fuel hose clamps from Pep Boys. They work perfectly. They will crack old hoses, so be prepared.

I had no problem changing the hose from the fuel tank to the elbow. $150 seems steep to me. That was one of the easier hoses for me to replace, but then I live in a relatively rust-free area.

DO FUEL WORK OUTSIDE where ventilation is better. Not because of the obvious benefits of not breathing fuel vapors, but because fuel vapors collect and can be ignited by normally innocuous things like the pilot light on a water heater or the motor from a fan. And don't use hot lights anywhere nearby. They can also ignite the fuel vapors.

The studs on my fuel pump are different sizes, one 8mm and one 7mm, so you can't attach the wires in reverse.

All work on fuel connections should use two wrenches. They are all designed for that. You should have a 19mm, two 17mm, and a 14mm wrench for the work. Use flare nut wrenches whenever possible and open-end wrenches only when necessary.

Pressurize the system and check for leaks before you put the protective cover back on.

Mike Heath
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino
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