Few quick questions now that my 1970 is finally running.

[D&W]

Originally Posted by mercmad6.3

My First mercedes was a 280SE which was 4 years old when i got it.I was picked up on radar at 125MPH and it wasn't working hard . I drove it at those speeds all the time in those days because it was built to do it and I did it.
I've had my 6.3 flat to the floor a couple of years ago for 2 hours (130-140MPH) when I was rushing to meet a boat ,again the cars were meant to drive at those speeds.
In both cases the cars were easy to drive that fast and in the second case I had never driven on those roads before.
If your car feels unstable at high speeds there is problems with the suspension.

Interesting... suspension replacement is beginning this week with some new shocks, then springs/pads/bushings to follow later.

What are the AUS transmissions like? I have a feeling they were delivered with different gearing rather than what is essentially a 3 speed in the states

[traumadoe]

Hey thanks, I took her up to 75+mph. Although the RPMs where higher than I would have pushed the IL 6 in my 59 GMC it was still accelerating steadily and didn't seem to be in trouble. I guess I won't be so shy with her anymore, she likes to run. I should have posted this question sooner, I have been white knucking down the freeway at 55 for a few months now afraid she was gonna pop!

[mercmad6.3]

59 GMC ??? you compared your Mercedes With a truck???

ha ha just kidding! Keep using your car and enjoying it!

[evoldeal]

Originally Posted by mercmad6.3

The radiator is not spposed to be filled to the top. There should be a gap of 1" between the top of the water and the filler neck. This is to allow for heat expansion. When you stop after a run,the heat from the exhaust mainfold is soaked into the engine( heat soak) and this heats the water. because there isn't any airflow over the radiator core,the water temp rises along with the pressure and the excess is spat out the over flow.
Your best bet is to make sure the engine doesn't go over 175 F when driving.
The top speed of your 250 should be 120+ mph. There is something wrong if it is struggling at 55MPH. Is it a C or CE ?

Mercmad my temp regularly goes over 175 when driving, especially long distances and in very hot humid weather. Also when stopped in traffic it can really spike, always drops quickly when you accelerate again. The temp fluctuates a lot actually, but I'm told this is normal for the model. Driving under normal heat conditions it runs just under 175.

All in all there is a 212f mark that you really don't want to be going over, but even that isn't even close the the red line..i

And to the OP, my car is also revving high at highways speeds over 70, but I've got used to the feeling; it's just cruising right along.

[mercmad6.3]

the temp should be stable ,What your symptoms sound like is a faulty fan clutch because your temp drops when you drive off from a stop (at lights etc) .
I am finding some M110 powered cars are getting hot at high speeds because of poor fuel quality. A higher quality fuel with no methanol seems to fix the problem.

[evoldeal]

hmmm you imply that my clutch fan is not turning?

I will check tomorrow. But i'd think that without a clutch fan, overheating would be quite drastic.

[mercmad6.3]

If your car has done 80,000 miles and the fan is original it's time the clutch was changed. They last around 60,000 miles. The fan will still be turning but if the clutch isn't giving enough "grip" to the fan,it won't pull enough air through the radiator. it's a common fault and your symptoms fit exactly.

[Rahulio1989300E]

Yeah man, if the fan clutch is dying then it will start to overheat when at a stop on hot and/or humid days. My 300E needs a new fan clutch, once I button up the 280C, I need to spend the cash for a new one and get it installed ASAP.
There are two ways to kind of tell if it is bad.

1. If you switch off your car with the hood open from full operating temperature and the engine cooling fan keeps spinning more than 3-4 seconds afterwards, it basically means that your fan clutch is bad.

2. I am not a fan (no pun intended) of this one, but you can stick a rolled up newspaper into the path of the engine fan.If the clutch is healthy, it will shred the thing to pieces. However, if your clutch is near death and you try this stunt, it may actually cause the fan clutch to fail right then and there since the resistant force of the newspaper may be too much for the remaining clutch friction material.

[evoldeal]

Well I'm glad I chimed in in the first place!

THanks mercmad and rahulio for the info. I'll go look into it now

that's why I love this forum so much. <3

[Joe Schmoe]

1970 280SE/8 (inline 6) Anybody ever see the auxiliary fan activate when the temperature spikes? It's supposed to be activated by the switch on the gooseneck. Thanks.

[traumadoe]

I have the piece in the water neck and an auxiliary fan but, the temp gauge is the only gauge in the car that doesn't function. I am waiting on a new one as we speak. It makes me nervous in this Az heat knowing the head is aluminum and knowing the cost of replacing or repairing/rebuilding the head now. I am not sure if the auxiliary fan only comes on with the a/c or if the temp goes too high.

[Mike D]

Ground the plug of the aux. sending unit's wiring. The fan should come on. If not, then check for bad fuses and the fan relay. The old relays are mechanical and have a nasty habit about sticking. Most of the time you can gently open the case, a quick zap of electronic cleaner, a blast of low pressure air, close the case and you're back in business. You can replace the old relays with newer electronic units but it takes a bit of re-wiring.

[evoldeal]

the fan comes on at 212f..

I topped off my radiator today after this talk about clutch fans etc. My clutch fan seems to working fine.

But I pulled in and shut off the engine tonight, sat in the car for a minute and next thing I know smoke is pouring out from under the hood. I ran to get an extinguisher and opened and I realize it is radiator fluid/water burning off on the engine and dripping under the car.

I don't know if it was coincidence with filling it up or what, but I'm completely freaked out to find out what is wrong.

[Joe Schmoe]

Originally Posted by Mike D

Ground the plug of the aux. sending unit's wiring. The fan should come on. [...]

Originally Posted by evoldeal

the fan comes on at 212f..

It is the 100 C switch and grounding the wire causes the aux fan to go on. Works without AC. There's a hood interlock switch near the extreme left rear of the engine compartment. Push that and stay the hell away from the fan.

I also removed the switch and checked it in a pan of boiling water. It's ok. I've *never* seen the aux fan go on under driving conditions, even with a scary looking temperature spike while idling. Has anyone observed the fan to work under driving conditions? I think the temperature sender is near the rear of the engine block and that region may be getting poor coolant circulation when idling. Thanks.

[mbbuff]

Pretty much what everyone else has said, but I have a little something to add, FWIW. I have a '67 250S (same engine as your 250C) and a '73 280C. The cooling systems on both look identical. The 250S cooling system is stock and I've converted the 280C system to a completely electrical system. You said you "topped" off the radiator. Without a coolant recovery system you can't fill it to the top or it'll spit like you said, until it seeks it's own level. I have found on my 250S that this level is about 1/2-3/4 in. above the core. This allows for expansion without overflow. A good thermostat and cap are also very important. On the 280C I switched it over, because it needed a new fan clutch and I didn't like the price of a new one, plus I always had a slight heating problem in town stop and go with the A/C on. I now have a 14 in. thermostatically controlled fan replacing the stock one, and a 16 in. auxillary fan in front of the radiator that comes on anytime the A/C is on or the coolant temp. reaches 100C with the A/C off. I've had this setup for a little over a year now, and so far it works great.

On your highway cruising comment, I think you've found the secret. On my 250S, at about 50-60 mph it sounds like the engine is wound tight and laboring. Get it up to about 70 and above and it smooths out and seems fine. I think that when these things were built the speed limits were less and they may have been geared more for that era. As others have said, you could probably drive it all day long at 75-80 without adversity, as long as everything is mechanically sound. Enjoy, they're great rides.