Hello~

This is an amazing message board. This is my problem, the steps I have taken.

I have this 1973 450 SEL. Its an electronic fuel injection gas V8. Recently, it started over heating. After a few minutes of driving it would shoot to the red line.

I immediately replaced the water pump, the thermostat (67 degree C type) and the main hoses.

This seemed to fix the over heating problem. Now when I drive for long distance at above 55 MPH the car will go above 175 on the dial and continue up if I don't slow down. I drive at 65 and after 45 minutes the temperature will go to red line at 250.

After careful research, I replaced the 212-switch which turns the electric fan on at 185 degrees F (I think). The belts seem okay and the radiator was replaced 2 years ago and I recently flushed it out. I also replaced the radiator cap because the old one didn't work.

Now the constant high temperature and high pressure is causing the expansion tank to leak at the seems and the hoses are going one by one. I guess they are very old so I am okay with replacing what needs replacing.

I use a 75/25 anti-freeze/water mixture. I use 10W-30 motor oil Chevron brand. I drive fairly easily, no racing or towing. Poor gas mileage.

MY QUESTION: Why is it running hot at high speeds?


Of all the things I have done, I haven't changed the fuel filter. I haven't checked the timing. I haven't checked any vacuum hoses. I haven't checked the injectors. I have recently changed the spark plus and one of the wires may be "leaking" but I doubt it.

Any help would be greatly appreciated! I am trying to restore this classic and I want to ensure long life. Please help. I am desperate. Any input would be great.

Thanks

About the only thing left is the radiator. Pull it, take it to a radiator shop and have them clean it for you or you could replace it with a new one.

__________________
Jim

Thanks for the reply. I felt that may be an option, however, after reading some of the other posts listed on this board regading high temperatures and speed, is it possible that a vacuum leak, timing or fuel mixture/CO2 level are off as well? The reason I ask is that it was listed on other models and years, I was wondering if that is possible for this year car.

Again, thanks!

I don't think tuning. etc will cause it to overheat like what you are saying. How's it running? I still think the radiator probably needs a good cleaning.
I have seen new MB thermostats not work as well as some from the local parts places.

__________________
Jim

Did I read correctly that you are using a 75% antifreeze to 25% water mixture?

That is awfully high on the antifreeze. Try changing to 50% or even 40% antifreeze.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Thanks for replying 'suginami'. I agree and I will adjust the mixture. It keeps leaking out so fast through all the different problems I've been having with the cooling system that I simply add anti-freeze one time and water the next time I check the levels.

As greatful I am for any input on getting my beauty fixed, I still need help getting the overheat problem fixed. As for 'engatwork', I replaced the thermostat with a generic NAPA thermostat which looks a little different from the Behr model pictured at The Benz Bin but I figured as long as it opens at 67 degrees C its okay. Besides, it runs hot only after driving at least 45 minutes at 65 MPH or higher.

The car runs okay disregarding running hot. It idles really low sometimes at the point of stalling. It is fairly quiet except for a couple exhaust leaks. Drives and shifts smooth.

Thanks for all your input. I flushed the radiator, but I will certainly take the radiator in and have it checked out if nothing else can be done. The ***** about it is that this model sends its ATF through the bottom to help the ATF cool off. How about vacuum leaks as mentioned on this thread? Also, should I have copper or platinum core plugs in this year and model MB?

Cheers,

The advise from the techs is unanimous.

All MB's made before 1997 were designed to run on plain Bosch or Beru copper plugs. They just run badly on platinum plugs.

Many techs on this site are reluctant to answer bad running / idleing questions if the car has platinum plugs.

Also, there have been others on this site with hot running issues that weren't solved until the radiator was traded out.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Sounds like a classic rediator problem. As with most things, the Mercedes seem to have 8 million different ways something can go wrong. But this sounds like a classic radiator problem. The rediator is clean enough and efficient enough to cool the car at low load but as soon as you call for more power and heat the radiator can not disapate the heat fast enough and you overheat. Had this exact thing happen with my Nissan (89), could idle all day in 100 degree heat with AC blasting, get on highway and instant over heat.

No one likes to replace a radiator (cost) but sounds like you might need to.

Good luck,
Joel

You kinda rang a bell when you mentioned "leaks". A partially suspect plugged radiator and leaks do not help your running hot issue. You should try to stop the coolant leaks while the radiator is out. If you ever get a chance take a look at a pressure-temperature chart for the relationship between the temperature and the system not holding pressure.

__________________
Jim

you mentioned a low idle,plus overheating.
I would have a shop check/set the Timing,get some bosch plugs and get the antifreeze mixture correct.These things need to be done anyway.then go from there.

__________________
'60 190b
'77 300D
'78 240D
'82 300TD

Yeah, and I'd print out this post from Stevebfl. He wrote the mother of all postings on properly setting the timing on a 450 SEL. The car in question on this post is also a '73 model.

gas milage (1973) 450sl

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Overpressure and overheat at speed are classic symptoms of a bad head gasket, too.

You must correct all the leaks before you can test this, though-- if the system won't hold pressure, it won't cool properly since the coolant will boil in the head, and vapor won't remove heat properly.

Make sure you are cleaning the hose nipples when you replace hoses, too -- if there is much scale or corrosion present, the hose won't seal.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks ya'll for responding to my questions. I've gotten good feed back and the more I get, the closer to my fix I get.

Yesterday, I removed the Bosch Platinum plugs and when examining them, I found that they showed signs of cylinders running too hot. I replaced the plugs with Bosch Copper plugs.

I drove 2 miles and suddenly I get this loping feel. So bad that it sounds like maybe more than one cylinder is misfiring!

I drive home and remove the plugs. They are covered with black soot. Some plugs are slightly moist. I start the car and it lopes like a misfire. I put a stethoscope to the injectors. Sure enough 3 of my 8 cylinders injectors aren't clicking. I messed with the Emmisions Control Unit (ECU) earlier to make the misture a wee bit richer or leaner because the MB tech told me it may be running hot from a lean mixture. 1-800-222-0100 option 7 and asked to speak to a tech.

I guess now I have two problems. The over heat is probably from the radiator so I will get that fixed right away. Is all this mixture/CO2 stuff somehow related to my over heating problem?

I started a new thread 1973 450 SEL injectors not clicking for this new problem that has occured.

However, thanks for all of your input!! I will get the radiator serviced, then I will work on the details you all mentioned. I will make sure I use the right mixture of AF and water.

Thanks!

Michael:

Check the ground for the injectors (probably on the firewall, an big bundle of brown wires under a bolt). It's behind the battery on the W108, but I don't know where on the W116. They fire in pairs, so if one works, the other in the pair should.

Other things to check are:

Injectors themselves -- they do occasionally go bad. Resistance across winding should be 2-3 ohm.

Trigger points in the distributor -- but as I said, the injectors fire in pairs, so either two or four should be out, not three. Four "points" under the point plate in distributor.

Rich running can be caused by a loose temp sensor wire to air cleaner (easily pulled off, I've discovered), a bad coolant temp sensor, or loose wire there, or worst, at bad MAP sensor. $375.

Bad throttle position sensor.

Cold start valve sticking open, will make for very rich running.

One final thought -- if you have an ignition problem (cracked wires, for instance, from changing plugs) you may be running rich from low vac -- this system doesn't measure air flow, just calculates it from MAP and throttle position.

I've been looking through the Bosch manual while writing this, and it sounds like you may have some bad injectors. The plugs will be burned on the cylinders with faulty injectors if they don't open properly, but do deliver enough fuel to ignite (lean running only on those cylinders). When the quit completely, you ened up with a rich running condition because of low vac and large throttle opening.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks for all your replies.


The injector problem is a different story but thanks for the help.

I took the radiator out and took it to a pro down the street. It has a 2 layer, 12 fold core in it and it should have a 3 layer zigzag or staggered 14 fold core.

This has got to be my problem. The guy said that the wrong core can greatly reduce the cooling abillity of the radiator! Up to 50% in my case.

Anyway, I have to decide to recore $502 or buy new $800.

Then we'll see if it still overheats. Looks like the previous owner either was ripped off or got cheated.