R107 500SL cooling problem

[Jay Kilby]

OK folks here is the problem.
from cold my car will heat right up to the red before the thermostat will open!! and then return to normal. this happens every time i start her from cold.
now if you drain the system then refill she behaves perfectly with no problems at all, but after a couple of cycles she goes back to normal. i have done everythig i can think of to cure this as listed below. any help would be great.

new M/B thermostat
new M/B thermostat housing
new M/B water pump
re-cored rad
full engine flush
all pipework removed and checked (including heater matrix)

is there a knack to re-filling these things as she is behaving like there is an air lock. but the thing is if i drain the fluid and re-fill her (i am a dab hand at this now) everything works properly. it is not untill a couple of on road cycles have happened the problem rears up again.
the only thing left to replace is the header tank if that fails then i am at loss. any help would be a great help.

thank you

 

[Myros]

Jay, the only thing you haven't changed

is the temperature sender. It might be worth a shot in case it's giving you a false reading

 

[Jay Kilby]

sorry already replaced that sorry did not mention it.

 

[television]

This is hard to say, see what happens if you start up from cold with the pressure filler cap off or lose

 

[Jay Kilby]

what are you thinking then Malcome. the header tank is about the only thing i have not replaced. i was thinking of replacing it anyhow as it does look a bit manky.

 

[television]

what are you thinking then Malcome. the header tank is about the only thing i have not replaced. i was thinking of replacing it anyhow as it does look a bit manky.

I just wondered if the circulation would behave differently when not under pressure, and allow any air to escape,it was a long shot, the header tank cant cause the problem in itself

 

[Jay Kilby]

well Malcome tried your suggestion but no differance however i am now thinking it is the guage itself. interestingly i have a electric fan conversion which takes the temp from the top hose from the thermostat housing. the thermostat is definatly opening i know this because the fan is set to come on at 80degrees and it does cut in but does not stay on even though the temp guage is reading in the red? so i am off to halfords to purchace an electric temp guage to check this theory out!!

 

[television]

well Malcome tried your suggestion but no differance however i am now thinking it is the guage itself. interestingly i have a electric fan conversion which takes the temp from the top hose from the thermostat housing. the thermostat is definatly opening i know this because the fan is set to come on at 80degrees and it does cut in but does not stay on even though the temp guage is reading in the red? so i am off to halfords to purchace an electric temp guage to check this theory out!!

Its possible the the sender is not man enough to have anything else joined up to it, might be better with a relay added

 

[Jay Kilby]

wow quick reply there Malcome!! i will disconnect the current guage once i have proved / disproved my theory i will re connect it and pull the dash out and clean the original see if that makes a differance i might even replace all the fuses with new ones as they are all looking a bit manky!! just want to put my mind at rest that my hunch is right and it is not overheating, i am convinced if it were i would have blown a head gasket by now!!

thanks