R107 1988 300SL cooling problem

[shakeel]

First post and first R107, so excuse my ignorance

Just bought R107 and it runs at around 70 degrees on the temp gauge instead of 88 as I expected. Heating in the cabin very poor. No oil in the antifreeze I can see, no water on the oil dipstick. Top rad hose pretty hot. Antifreeze in the overflow chamber pretty hot, but not burning.

I wondered if I'd start by removing the thermostat to see if it's stuck half closed.

Is this a problem... perhaps an airlock?

Any pointers much appreciated

 

[Aussie Nick]

Try replacing the Thermostat .What condition is the radiatorcap in. If it is an air lock there is usally a bleed screw or bolt somewhere near the top of the block.You could loosen this off and run the motor for a a few minutes and monitor to see whether bubbles come out as well as coolant. If this does not work you may need to take the radiator out and have a specialist clean it.This normally involves taking off the top tank and running a thin wire through all the orifices to clean them out. If the radiator is blocked you should try running a skinny long wire through the heater hose back in towards the cabin and through the firewall. You can then run a compressed air nozzle into the open end of the hose to try to move any foreign substance through and out of the system.
This generally works but in some cases it dosen't totally cure the problem.There should be major improvement in the heater performance though.

 

[television]

If it is running cool, normal is 80c then only the thermostat at fault.

The heater is normally the duo valve stuck, see DIY section

 

[shakeel]

Cheers Television, and Aussie Nick. I'll try the changing the thermostat.

Got new info... in traffic, the engine ran to 95' yday.
And the heater got very hot (so the duo valve isn't stuck).
Once i got moving again, temp cooled to 50' and the heater cooled down.
I'm not losing coolant.
This suggests thermostat stuck half open/half closed again i think.

Thanks again for your help

 

[star]

def thermostat stuck half open, there is no duo valve on this car, just an on/off valve and heater flaps. just check that when stat is changed, your fan cuts in bout 100 c mark.

 

[shakeel]

Cheers Star, off to Mercedes to get a stat now

 

[television]

def thermostat stuck half open, there is no duo valve on this car, just an on/off valve and heater flaps. just check that when stat is changed, your fan cuts in bout 100 c mark.

Thats good news anyway, its surprising how cold a heater can feel when running cooler than normal

 

[shakeel]

Good news, new thermostat and rad cap, and she now runs a constant 87'
Heater is better... tho' not hot
I'm guessing airlock somewhere.
Is there a knack to bleeding these engines?

 

[television]

The only way is to remove the cap and squeeze the bottom hose a few times

 

[star]

remove rad cap, turn heater on full heat and fan is on, run engine at high rpm (2500), keep checking temp guage but shud blow thru heater, check level again.

 

[Aussie Nick]

There should be a bleed screw on top of the block.

 

[television]

There should be a bleed screw on top of the block.

MB,s do not have them

 

[shakeel]

Bleeding hasn't really been successful.
Eng runs constant 87 except in traffic in hot weather.
Heater still good, but not right until when stationary in traffic, temp rises to 105, heater is beautifully hot.
One post mentioned to check that my fan kicks in at around 100.
However my fan seems to be a torquodial fan, always running.
I am unsure how to proceed.
Is this rise in temp to above 100 normal?
Thanks for continuing advice

 

[mercy nick]

Bleeding hasn't really been successful.
Eng runs constant 87 except in traffic in hot weather.
Heater still good, but not right until when stationary in traffic, temp rises to 105, heater is beautifully hot.
One post mentioned to check that my fan kicks in at around 100.
However my fan seems to be a torquodial fan, always running.
I am unsure how to proceed.
Is this rise in temp to above 100 normal?
Thanks for continuing advice

M103s are prone to blocked radiators, the inlet and outlet on the same side is a bad idea for flow.

If you put yout hand on the radiator, are there any hot spots?

 

[shakeel]

Took car to John Haynes Auto Technics near Worthing. New radiator, rad cap, hoses, thermostat housing and thermostat fitted, as well as a hundred other things they found wrong with the car! It runs much better now

Heater now very hot on defrost mode, air blowing towards the windscreen. Heating intermittent to the cabin, sometimes very hot, then medium temperature. Sometimes cool.

When I'm in traffic, and temp rises to about 95'c then everything's perfect. Otherwise, so-so.

Tried running with rad cap off, squeezing bottom hose but to no avail.

Can I fit a higher rated thermostat, say to 95'c

 

[roofless]

if you find the highest point in the cooling system loosen the hose just a bit to let the air out when it's at running temp it might help

 

[shakeel]

Ok thanks Roofless, I'll give it a go

 

[television]

There appears to be only one stat listed for that model

 

[shakeel]

Not having any luck with the bleeding.... still great defrost, lousy on the feet unless i'm in traffic and the engine temp rises to 95'c

What might the impact be on the engine if i can find a 95'c stat to fit?

 

[Craneboy]

300 sl

Hi,
I had a 300SL 107 and had similar problems with it to the point of almost pulling me hair out. I change the thermostat and housing to the improved sort with the bleed screw on top, which was a help.
Then the temperature went through the roof and thought i had cooked it, which luckily i hadnt, then put the car into Mercury at Aldershot who relieved me of £1045 for new radiator, water pump and viscous fan. a lot of money but problem solved.

Its damned frustrating with issues like this.

Tony