Coolant system problem - PeachParts Mercedes-Benz Forum

ck42 · #1 08-23-2014, 04:02 PM

Little issue with the coolant system.

Car has been sitting 5 yrs. I've refilled the coolant system (was empty all this time).
Started the engine and let it idle for 10-15 minutes.
Top hose is nice and hot. Bottom hose is cold - not even warm.

Temp gauge on the dash hasn't budged in the slightest. Says it's stone cold.
Cranked on the heat to the car. Blew cool air.

Wondering - could it be a stuck thermostat? (stuck closed?)
Even so though, with the top hose being hot, shouldn't the temp gauge have been reading this? which of those three sensors in the thermo housing is the one for the dash gauge?

[EDIT]

Found the reason for the non-functioning temp gauge. The connector to the sensor, behind the IP, was unplugged for whatever reason.

I'd still like to know though if coolant is actually circulating. Short of waiting to see if the temp gauge shows the engine overheating, are there any quick tests I can perform to verify all is good?

leathermang · #2 08-23-2014, 05:02 PM

Why don't you take the coolant out of the system by taking the lower hose off at the radiator.... have you a catch bucket so you can reuse it....
Also... the lower hose needs to have metal spring inside.. it is a suction line.. and if you can squeeze it...then under load it will close on its own... causing overheating...which can not be seen at an idle... so hard to find unless you know to squeeze that hose...

ck42 · #3 08-23-2014, 05:21 PM

Bottom hose can be squeezed...if I grip it pretty good. It's not totally rigid, if that's the impression I'm supposed to get.

Skippy · #4 08-23-2014, 05:24 PM

I don't know what car this is, but if it's one with a cap on the radiator, you should be able to see coolant movement from the water pump after the thermostat opens.

leathermang · #5 08-23-2014, 05:52 PM

At speed that water pump can produce a lot of suction..
would put new lower hose on.

Mxfrank · #6 08-24-2014, 12:37 PM

I've not worked on an SD, but on all the Mercedes I've owned, the heater is supplied via the electric aux pump, which draws water from the bypass circuit. So the heater should blow warm, but that may be another problem entirely.

I would just let the engine idle longer, keeping an eye on the gauge. If the temperature is above 85 and there's no flow through the radiator, that's when you worry. There's plenty of time to switch off before the engine overheats. It takes a long time for a Diesel to build heat at idle.

Not every Mercedes has a spring inside the lower hose...certainly the 60x engines didn't.

pimpernell · #7 08-24-2014, 12:54 PM

[QUOTE=ck42;3377080]Little issue with the coolant system.

Car has been sitting 5 yrs. I've refilled the coolant system (was empty all this time).
Started the engine and let it idle for 10-15 minutes.
Top hose is nice and hot. Bottom hose is cold - not even warm.

Temp gauge on the dash hasn't budged in the slightest. Says it's stone cold.
Cranked on the heat to the car. Blew cool air.

Wondering - could it be a stuck thermostat? (stuck closed?)
Even so though, with the top hose being hot, shouldn't the temp gauge have been reading this? which of those three sensors in the thermo housing is the one for the dash gauge?

System may have to be burped. If you have an air bubble in the block, it will stop the circulation through the system. Just put the nose of the car on a slight incline facing up, disconnect the top hose and see if you can add more coolant.

leathermang · #8 08-24-2014, 02:39 PM

This is not a ' Mercedes ' thing... it is a physics thing. All I know is that if you can squeeze it together with your hand... then the rubber can be sucked together by the water pump. It is one of those mechanic things that when you run across it... an engine overheating out on the road with Nothing else you can find wrong... will stick in your memory....because you can not get it to do it sitting still where you can see it.

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ck42 · #9 08-24-2014, 03:39 PM

All good ideas and things I can try to check! Thanks.

yuke · #10 08-25-2014, 01:12 PM

Try taking thermostat out and run it see if it makes differance. My 85 300 SD was running at a 100 and little above took thermo out then ran too cool. Drilled 3 holes in outer ring and runs right at 80c. Now just takes a little longer to get up to temp. Will put the stock one that opens at 176 in colder months. Thermos are cheap at $15. Did not feel like pulling radiator to have professionally flushed. Drilling 3 holes seems to have done trick for me read diesel giant write up on matter.

oldsinner111 · #11 08-25-2014, 01:21 PM

I always drill one or two 1/16 holes to let air bleed out,and run a little cooler.