450 SL running hot, please advise?

[stanm]

Hi! This forum has many knowlegable people so perhaps I can gain
insight on why my 1974 450 SL is running hot?
First, the needle reads at the 200 degree mark on the gauge [in traffic].
On the freeway, the needle drops just below the 200 degree mark.
A year ago, it would run at the 175 mark all the time.

I have already: Replaced the thermostat and R&R radiator to have
it boiled and rodded. The radiator shop guy said it was blocked, about
40% and should run cooler however, upon installing the radiator and
adding 1 galon of anti-freeze, the temp is STILL running at just a little
below the 200 degree mark. Oh yeah, I did replace the temp sending
unit with a new one and a cooling system pressure test holds 15psi
for at least 15 minutes.

WHAT HAVE I MISSED???? PLEASE, give me your thoughts!!!!
With warmest regards,
Stan M

[Lawrence Coppar]

I have a Porsche track car. A number of years ago the temperature was running a little high at low rpms such as when I drove it to driving events and had to climb some hills in northern GA. On the track at high rpms, the temperature would remain normal. I would have to turn the heater on while climbing the hills to keep temperature from running up - either that or use lower gears to keep the revs up.

In my case it was a water pump that was not putting out sufficient flow at low rpm. Corrosion had increased the clearance around the impeller and reduced pump output.

Another thing you can check is your AC condenser that sits in front of your radiator. The things get all sorts of junk in them that cuts airflow through the radiator. About the only thing I have not found in my condenser is money.

[page62]

My guess is it's the temperature sending unit. They can have a large variation in reading from one unit to another.

The best way to check your engine temp is with an infrared temperature sensor. I just saw a Carquest flyer advertising one for $49.95. This will give you an idea of how well (or poorly) calibrated the sending unit is.

[Walrus]

Originally Posted by stanm

First, the needle reads at the 200 degree mark on the gauge [in traffic].

...A year ago, it would run at the 175 mark all the time.

Replaced the thermostat...

Hi,Stan.

Let me start by stating that 200F is not hot by a 107's standards... After much exhaustive research, I have discovered 85-90C is where the cars need to run to be most fuel/emission efficient, and were designed for this range. That said, I have also had personal experience with the same situation you did, as well as have others... Replace the thermostat and suddenly, you are running hotter than before. The answer lies partly in the fact that the older stat was probably stuck partially open. Seems the stat is designed to START opening at 85C, and is not fully open until 94C... Since it is a two-stage with incorporated bypass, a partially stuck stat will cause abnormally cool running. Many an owner has had service to the cooling done, only to experience higher running temps afterward! You have done all that you need to rule out most culprits, with the exception of water pump and AUX FAN ( I do not believe you have a two-stage, viscous clutch on your fan...can't recall if/when 450s did).

Incidently, 85C=185F 94C=201.2F

[stanm]

Hi Walrus!
Thanks for the reassurance with "Normal" running temps.
She is a bit of an old girl and I don't want the poor car to
suffer. I did take a digital temp reading at the top of the
radiator and it was about 95c and since summer is just around
the corner, I wasn't sure how much the running temp would
creep up when the ambient temp starts to get hot.

Also, I didnt' know how much the water pumps are prome to
failure. The pump looks like it's been in for a while and the
engine itself has pretty high mileage on it. I'm not sure that
I want to throw a bunch of parts at it, especially since it
may be a common thing with these old 107's.
Thanks again!!!! & let me know if you think of anything else.
Cheers.

[Robert Mowbray]

Dump in a bottle of Water Wetter. It'll drop the running temp between 5 and 15 degrees. Happy Thanksgiving

[stanm]

Thanks Robert but I'm not familiar with "Water Wetter", what is it
and where can I get some?

I did add anti-freeze @ 45% strength when I repalced the thermostat
but had little improvement with dropping the temperature. I was hoping
to raise the boiling point and perhaps making it run a bit cooler.

Today I repalced the water pump and it STILL runs as hot as before....
Any other suggestions would be very welcome at this stage!!!!
[I am willing to try the watter wetter, who knows???]
Happy Thanksgiving! Stan

[waybomb]

Look, move up here to Michigan - it is about 15 f right now - probably would run at 175 today up here!

Seriously - 200 f in the cooling system is ok. If anything, I bet a good radiator / cooling system flushing would help get it down a bit.

[Benzmeister]

Originally Posted by stanm

Hi! This forum has many knowlegable people so perhaps I can gain
insight on why my 1974 450 SL is running hot?
First, the needle reads at the 200 degree mark on the gauge [in traffic].
On the freeway, the needle drops just below the 200 degree mark.
A year ago, it would run at the 175 mark all the time.

I have already: Replaced the thermostat and R&R radiator to have
it boiled and rodded. The radiator shop guy said it was blocked, about
40% and should run cooler however, upon installing the radiator and
adding 1 galon of anti-freeze, the temp is STILL running at just a little
below the 200 degree mark. Oh yeah, I did replace the temp sending
unit with a new one and a cooling system pressure test holds 15psi
for at least 15 minutes.

WHAT HAVE I MISSED???? PLEASE, give me your thoughts!!!!
With warmest regards,
Stan M

this time of the year in New England at 175F and will hit 200F at times. The private Mercedes shop I use for my daily driver a 99 C280, has looked over the 450 and he said the temp range is normal, In fact according to conditions and where and how you are driving, as long as you don't get into the read and the temp drops after say you stuck in traffic etc. Everyhting he checked is fine. Consider this my 99 C280 runs between 80C and 90 C 80C is my math is correct is 212F, and this is normal operating temp for the V6. Eve back then especially when cats were installed, cars engines were designed to run hot, to meet EPA standards of the time. The hotter it runs the more bad stuff is burnt off. I started a grass fire at a Porsche event years ago when I owned a 86 911, It was parked in a field, and the cat was so hot the grass started smoking, I jumped into the car so fast and drove it off the stop, I thought I was moving at warp speed. So unless you start over heating I wouldn't be too concerned. Watch the gauge. Also the shop owner flushd the cooling system and used Mercedes antifreeze mixed 55/45, he advised to keep the enginer running at the correct temps and to help the ACC servo last longer, change the anti freez faithfully at least every two yearrs, He owned a 78 and changed the anti freez once a year. I post some information on the older Mercedes forum, before I spotted this one. I need some advice and help with a few issued. Thanks!

[Benzmeister]

Originally Posted by stanm

Thanks Robert but I'm not familiar with "Water Wetter", what is it
and where can I get some?

I did add anti-freeze @ 45% strength when I repalced the thermostat
but had little improvement with dropping the temperature. I was hoping
to raise the boiling point and perhaps making it run a bit cooler.

Today I repalced the water pump and it STILL runs as hot as before....
Any other suggestions would be very welcome at this stage!!!!
[I am willing to try the watter wetter, who knows???]
Happy Thanksgiving! Stan

It did nothing to lower the operating temp, but it might work on these older our cars, but as I said in my post and I see most agree 175F to 200F is what my runs at. One more point when it starts to move toward the 200F turn on the AC or heat according what time of the year it is, or the derfroster as the AC kicks on no matter what the ambient temp is, as the AC defogs and it is designed to do this. This wil lower the temp, why? more coolant is criculating thru the entire system. When I tried this the temp dropped down to between 175F and 200F. But as I said in my other post not to worry, unless the gauge starts going to the red.

[Robert Mowbray]

Water Wetter or other collant additives are available at most auto part stores. Some additives guarantee a drop of 30 degrees in operating temp. Best of luck.

[stanm]

Okay, okay, you all have convinced me that as of this point, my car
is running within a reasonable temperature range. However, I will keep
an eye on the gauge especially as summer draws near.

What a FANTASTIC forum with such friendly and knowledgeable
people, I thank you all!!!!
Cheers!

[Benzmeister]

in November, so I have no hot weather experience myself, and I have an working sometimes aux fan. Which I still have to deal with.

Al

[Kebowers]

You got a real good clue from the radiator shop when they said 'it was plugged'.

In all probability the radiator still has a significant coating of scale inside the tubes. Get some heavy duty cooling system cleaner (citric acid or oxycalic acid types) or the Prestons stuff specifically for removal of 'solder bloom' and 'silicate scale.' Even a very thin film of the silicate crap will destroy the heat transfer ability of the radiator.

[Benzmeister]

and back flush it from the engine up thru the radiator. Also, George Murphy's material on the ACC Servo says to remove or disconnect it when you flush the cooling system as junk from the flushing could lodge inside the Servo and damage it. I got two pieces of hose and take all the hose off the servo, and the pre heater and then connect the piece of hose i bought so the back flush passes thru the heater core an by passes the servo and the pre heater.

There a site I come across that claims they have a digital replacement for the ACC servo, the address is http://unwiredtools.com/accii.html. This is the second company that claims they have a all electric replacement. I know Phil sells a updated replacement as well and Performance Analaysis both are aluminium instead of the plastic. Unwired tools doesn't quote a price, it says call for pricing. Performance Products in CA want almost $1600 for an brand new sero. Interestingly on the unwired site you can download a handbook in PDF on the operation and maintenance of the servo. It was published back in the 70's by Chrysler, as they used the same servo in there heating systems. for a few years.