Weird circumstances:

On the way home for work, the coolant light comes on.

So I watch the temperature gauge as I drive it to the nearest gas station, about two miles away, the temperature NEVER GOES UP from 90-C, stays steady (it's about 84-F and 70% humidity in Florida).

I finally get to the gas station, and feel the upper-radiator hose and there is NO pressure.

There is also no visual leaks or puddles of coolant anywhere.

I carefully remove the coolant-cap, and add some water, and drive to my destination another 3-miles away.

I park, and notice no leaks during my 30-minute pizza diversion.

I start the car, temperature is fine, and no coolant light, so I drive home another 3-miles.

When I get home, I pop the hood, and again there are no visible leaks, and the upper-radiator hose has NO pressure, hence I carefully remove the coolant-cap.

Then all of sudden medium-pressurized hot-coolant comes bubbling out, but not under the normal pressure.

I felt the thermostat bypass hose and it is hot, so it seems like the thermostat is working.

I know I need to pressure test it cool, but any ideas ?

Thanks,
:-) neil
1993 500E
(new hoses, radiator, thermostat about 3-years ago)

After about a 30-minute cool-down, I noticed the following:

1) the lower radiator hose is cool to the touch, but the upper-radiator, thermostat by-pass, and block-to-thermostat housing hose were HOT to the touch.

2) the lower portion of the radiator is cool to the touch, but the upper half of the radiator is HOT.

Are these the symptoms of a failed waterpump (110K miles, original) (hence no pressure) or a clogged radiator ?

I highly doubt the radiator at 3-years old is clogged . . .

I put a stethoscope on the water-pump at idle, but I don't know what I should hear ?

TIA,
:-) neil

A couple things. First, the water pump does not create the pressure in the cooling system. Heat does it, and the pressure is held by the radiator cap. Ideally, the cap should vent air when the pressure rises above whatever the cap is rated at. When the coolant cools off, the cap should then allow air to enter the cooling system and thus avoid a vacuum. A failed pressure cap could account for the small loss of coolant.

Second, if the water pump bearings were bad, you'd hear it through the stethoscope. Listen to other bearings under the hood and compare what you hear.

Pressure test the cap when you pressure test the rest of the system.

__________________
1989 300 SEL that mostly works, but needs TLC

likely either the cap or the reservoir. This will eventually cause overheating.

__________________
89 300te 222,222
92 300e 190,000

Are we certain that the "coolant" light that came on is the RED one with the thermometer indicator?

I had a heater hose blow once with coolant splaying everywhere, temps over 120C and smoke out of the hood, and that light never came on!

To me, I would guess that the AMBER "coolant level" light is the one that lit up. The symbol appears as a cross-section of an engine with a water wave-like icon.

I ask this since temps seemed to be normal nonetheless...and when the coolant pump goes, there WILL be a pool of coolant all over your garage floor as the engine cools down.

The coolant level sensor does corrode over time and give false readings. A FastLane replacement may be in order. Inexpensive and simple to replace.

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

False positives are the normal failure mode of the coolant level sensor. I had to replace the one in WMBO's 1993 300E within the last year. About $20 for the part, IIRC.

Keep tabs on the coolant level. If it doesn't drop, then it's time to convict the level sensor. BTW, if you have the reservoir more than half full, you might lose some coolant due to normal heating and expansion. In that case it will, over time, drop to the normal level and remain there.

No pressure in the hoses is not right - they should be quite firm with the engine at 90C. Pressure cap on the plastic tank is the first item to replace. The plastic tanks are known to not last forever either.

Only 84 degrees? Must be nice.

- JimY

If the coolant level drops to the point where the "low coolant" light illuminates the engine won't overheat because there is still plenty of coolant in the system - just as your engine won't be damaged if the oil level drops low enough to illuminate the oil level indicator. They are both warnings that these fluids are at minimum level and should be serviced soon.

Has the coolant been changed recently? On a coolant change it might take a few heat cycles to purge all the air out of the system, and air in the system is indicated by a dropping coolant level. Following a coolant change, level should be checked after every cycle and coolant added as necessary. Once the level stabilizes, all the air has been purged.

The coolant level line on the plastic expansion tank is the "full cold" level. At operating temperature the level should be about to 1 cm above this line.

Lack of pressure holding is indicative of a faulty pressure cap. Most autoparts stores have testers to check them, but be sure you buy a cap that is correct for you model: "120" caps hold 1.2 Bar. "140" caps hold 1.4 Bar.

Duke

In one of the cars..don't know if it's the ce or e, the "low coolant" light comes on when the resevoir is at a highly suprising level. I just added a bit of water one time, maybe a cup...and it went out.

Over the years most of my "temperature" problems have been the direct result of a worn out radiator cap.

We tend to forget how old our cars are...

__________________
1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

Replaced the radiator cap, and still the system won't hold pressure, and discharges coolant after a 5-mile drive (this time to NAPA autoparts), thus making the coolant level light come on, but again, no overheating.

Luckily, I had placed in some coolant U/V dye and it looks like the rear hose from passenger-side block to heater-diverter valve (124.830.54.96) or the metal elbow that bolts to the block and gives it a nipple is defective.

Waiting for the car to cool before removing the hose to find out . . .

:-( neil

PS: the dye don't lie . . .

So, I have the 1987 300D coolant level drop syndrome, hoping it is not a cracked head. How did your situation turn out?

Yep, it was the rear engine hose on the passenger-side (USA) of the engine block that had a tiny slit, that was slow enough to touch the HOT engine and vaporize the coolant while driving.

BTW, about 2-months later, the other rear engine hose on the driver's-side that goes to the heater core, also had a small leak.

All is fixed, along with a new waterpump, thermostat, thermostat by-pass hose, waterpump to intake manifold hose, and lower hose.

:-) neil

Glad to hear! I hope I am as lucky! I just purchased a 1987 300D and was driving it home when the coolant light came on. Have not had a chance to analyze it further. The temperature never exceeded 90. I suspect it needs a little basic maintenance, as the PO only drove it 12-15 miles a day for the last two years and did nothing but regular oil changes. I will inspect all hoses, vacuum connections, etc. this weekend.