W140 Overheating

[ron_miles]

Anyone have any ideas ?

Recently bought an S500 w140 in what looks like immaculate condition only problem is that it appears to be overheating.
When starting from cold the temp gradually rises to about 80 but then continues to rise over about an hour to 115. The viscous fan and electric fans appear to be working ok and if I turn on the heater blower and turn up the temp the engine temp drops to around 100. The local garage seems tothink that it may be a blown head gasket or a faulty radiator, I'm thinking maybe a faulty thermostat or air lock.

Regards

Ron

 

[guydewdney]

thermostat is easy enough to change...

do the fans come on at 90ish degrees?

what year is it? pre- 96 is one system, post anonother - but might be worth replacing the temp sensor (easy - 22mm spanner and 30 seconds and 20 - 25 quid on a post 1996)

does it run like a bag of nails when hot (relativly - ie a bit lumpy) or is it no different? if you have the LCD display air con unit next to the radio - press and hold REST and EC together for 5 or so seconds - display changes. press lh auto button until lh display reads number 6 (ie press it 5 times) - the rh display is the temp in degrees C - just as a check...

 

[ron_miles]

Hi Guydewdney

Thanks for the reply.
My w140 is a 1993 LWB,the fans seem to be operating OK and there is a slight miss at times but not always when hot.
Checked the temp gauge with the LCD readout and they are the same.
Sometimes when I turn on the blower to reduce the engine temp it blows cold I then turn off the engine and re-start and it blows hot.

Ron.

 

[guydewdney]

well - change the thermostat...

iirc theres a 140 radiator on ebay at the moment...

 

[ron_miles]

That was going to be my next step.

Tried to find the radiator on ebay but nothing came up in the search, can you remember what heading it was under.

Ron.

 

[guydewdney]

That was going to be my next step.

Tried to find the radiator on ebay but nothing came up in the search, can you remember what heading it was under.

Ron.

sorry - straight after i posted i looked - but its gone... or i got it mixed up with the air con condensor on there...

 

[LNM]

Ron

_after_ my had was replaced, I drove for a few hours without a thermostat and temp was all over the place. For £15, get it changed. Its sweet as a nut now.

Check the coolant for mayonnaise (gd forbid on a V8) as an indicator that the head(s) (weep) may be gone

 

[guydewdney]

oh - and as its a pre- 1996 model - has the loom been replaced? the pre-facelift looms fall apart (check by peeling back a bit of loom tape on a non essential bit of the loom / a mini loom or short bit of wire - has the insulation gone brittle?)

3 - 4 hours and several hundred quid to replace - but not difficult - worth checking...

 

[ron_miles]

Well, removed the thermostat ( new one on order ),no difference. Flushed and backwashed the rad, no difference.
Engine temp will gradually rise to over 100c and keep going, put on the heater to max and it drops to just under 100c and stays there .
is there anything else I can try?

Spoke with the local dealer about the replacment loom but hewasn't aware of any problems with the W140!

Also any idea where Imight pick up an MPH instrument cluster as mine is in KPH.

Regards

Ron

 

[guydewdney]

hmm - water pump?

slipping belt?

twaddle about not knowing - try some of the yank forums about the wiring loom... scary pics on there (havent got a link to hand - somthing like benzworld.com)

 

[TheJim]

One other thing- what coolant are you using? Mercs are very fussy.
Mine was all over the place, put the merc coolant in 50/50 and the car now sits at 80 instead of 110.