Roy,

Actually, on older cars, the metal spring was in the lower radiator hose to keep the hose from collapsing while the engine was running.

With the upper hose collapsing when cold is a demonstration of thermo dynamics and the pressure inside the cooling system being less than atmospheric pressure.

This can happen if coolant level is low, as air is now in the system. Cold air contracts, warm air expands.

Opening the coolant fill cap will draw in air and equalize the pressure. It also means that your system is not venting properly, or you are low on coolant.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

A bad radiator cap prevents system cold equalization, generally called cold venting, and I see it often.
A cap is cheap, mine is replaced every year.

Your other points are also accurate.

Is that cap designed to prevent accumulated vacuum in the system.....and, if so.......to what level?

Most systems have an absolute pressure below atmospheric when cold.......after running.......as evidenced by the inrush of air when opened. All of these caps cannot be NG.........???

However, it is the cheapest ($7.50 USD) starting point for any cooling system diagnosis.

This is another reason why I replace the cap on my car every year, it gives me a known good cap for diagnosis.

This year the average for MB I worked on has been seven out of ten caps where bad.

I would rather replace three good caps, than miss one bad cap.

The cap, thermostat, belt and hoses are the cheapest units on your car, that can potentially wreck the engine.

What is your engine worth to you?
Would you knowingly choose to ignore/refuse service on these critical items?
My sincere hope is that no forum member would risk their engine over these cheap items.
The sad fact is that I see many MB that need all of these items at once, due to the previous owners LACK of maintenance.


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 300D Turbo
Part: Thermostat Kit
Note: 80 degree
G4001-49781 Thermostat Kit Wahler IN STOCK $24.50
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1YE1FF2PQ1YN0TDGMP&year=1987&make=MB&model=300-DT-002&category=All&part=Thermostat+Kit

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 300D Turbo
Part: Radiator Hose
Note: Lower
G2000-16382 Radiator Hose Germany IN STOCK $72.16
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1YE1FF2PQ1YN0TDGMP&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1987&product=G2000-16382&application=000017660


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 300D Turbo
Part: Radiator Hose
Note: Upper to thermostat
G2000-16376 Radiator Hose APA IN STOCK $11.81
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1YE1FF2PQ1YN0TDGMP&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1987&product=G2000-16376&application=000040490


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 300D Turbo
Part: Radiator Hose
Note: Lower
G2000-16380 Radiator Hose Lemforder IN STOCK $6.08
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1YE1FF2PQ1YN0TDGMP&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1987&product=G2000-16380&application=000040496


Vehicle: 1987 Mercedes Benz 300D Turbo
Part: Heater Hose
Select one of the products from below
-----------------------------------------
Heater Hose
12 X 19 mm : 1 meter
-----------------------------------------
Heater Hose
15 X 22 mm: 1 meter
-----------------------------------------
Heater Hose
18 X 25 mm : 1 meter
-----------------------------------------
Heater Hose
Valve to Auxiliary Pump Chassis: -A 289309
------------------------------------------
Heater Hose
Engine to heat exchanger Chassis: -A 289309
------------------------------------------------
Heater Hose
Recirculating pump to
return line Chassis: -A 289309
----------------------------------------------------
Heater Hose
Return line to engine
Chassis: -A 289309

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1YE1FF2PQ1YN0TDGMP&year=1987&make=MB&model=300-DT-002&category=All&part=Heater+Hose


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1987 Mercedes Benz 300D Turbo
Part: Multi Rib Belt
Note: 21.36 X 2145
W1000-21016 Multi Rib Belt Conti IN STOCK $27.03

W1000-21016 Multi Rib Belt Bando IN STOCK $20.92
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1YE1FF2PQ1YN0TDGMP&year=1987&make=MB&model=300-DT-002&category=All&part=Multi+Rib+Belt

Acc. Belt Idler Pulley
Acc. Belt Tension Adjuster
Acc. Belt Tension Damper
Acc. Belt Tension Spring