Hi Board i'm sure somebody here knows exactly my delimma. She is overheating, it just started for no reason yesterday. I immediatly shut off my A/C opened all my windows and turned on my heater (per emergency checklist) and looked for a safe place to land. Initial inspecion the engine had water although it was slightly low (added water and cooled radiator), belt ok. Restarted car to no avail. Let her sit till she cooled and drove her away. Heres the confusing part........everything seemed ok so i went to take her home and she starts climbing again noting no heat coming out of the heater vents, then this burbling sound and she starts cooling down and the heater inside starts blowing warm air. So thats the pattern for 20 miles home engine heating up with cold air from the heater vents then when she get to about 120C a burbling sound and warm air from the vents and she cools down to 90C. I figure this is thermostat. New thermostat and it still overheats. Is there another component such as a heater diverter that could cause this same symptom or could the blade on the water pump possibly be spinning on the shaft intermittently. New facts, fans work fine and no oil in the water,
no water in oil and water pump changed 80k ago.
Your help is greatly appreciated, thanks
Alex

1. Feel the radiator and all the rubber hoses cheking for blockage in the form of "cool spots".
2. Check for a water leak under the water pump. If you see it, the pump is gone.
Did you change the coolant with the right mixture of water/coolant?
Good luck!

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J.H.
'86 300E

Hi there,
Try checking this: fill the radiator completely full, then run the engine until it is completely warmed up and check for bubbles coming out of the water. "goose" the engine a few times while checking - once the coolant system is completely full and the air is purged from the heater, etc. there should be absolutely no bubbles emanating from the system. If there is you have a blown headgasket or a cracked block or head. (Usually a blown headgasket, 95% of the time). The combustion gasses will "blow" the coolant right out of the radiator while you are going down the highway, and the engine will overheat, the heater will stop working because there's no coolant flowing through it, etc.
Good luck with it!

RGW
'82 300D/4.3L V6
Etc...

Does anyone suspect the heater control valve?

Thanks guys, First the top water hose never builds pressure or gets hot (I Suspect it is during the occasional burbbling/cooling episodes its since i'm driving I can't check). I don't think its a blown head gasket and it never cools even with lots of cool water.
Next...........can the heater control valve prevent the whole system from recieving water?? And if so where is it located and what does it look like??
Thanks for all the assistance in advance
Alex

The heater control valve can not be causing your problem.
The top rad hose should become hot when the engine is at its normal running temperature. what you may have here is a circulation problem.
Blocked/clogged radiator, internally collapsed lower/upper radiator hose, defective water pump, defective thermostat (not opening), major air lock in the system.
Other possible causes: defective water reservoir cap
Combustion gas entering the cooling system (Faulty head gasket, cracked head.
Jackd

have overlooked the 'tstat'. Just because it's NEW, doesn't mean it's working ok! It could be stuck.

Also hearing 'gurgles' may mean the rad pressure cap is bad.

Since the car did NOT overheat until the new tstat was installed, I'd look there first! My 0.02 cents.

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Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Get a new pressure cap. I had the same problem on my 300TE when I bought it -- PO said "it had an overheating problem with the AC on but they fixed it" -- typical "soccer mom" didn't have a clue as to what they did.

Turned out the AC was discharged (leak at the expansion vavle), and when I charge it, it overheats on the highway. Would blow several quarts of coolant out when I stopped after a hot run. Put a new pressure cap on, and it only gets too warm in traffic now (need to install the new visco clutch this spring).

You could also have a bad thermostat, in combination with the bad pressure cap the coolant will boil in the head and prevent circulation.

Thermostats are cheap, and easy to replace, so I'd do that too.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Any coolant purging from the overflow tank on right side just behind the front wheel? If so, then the cap is probably the culprit. If not, it sounds to me like a bad monovalve with the way your heat works intermittently. If this is the case, depending on model year of your 300E you can repair or you must replace the monovalve to solve problem.

Good luck,

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-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi

Great Guys thanks, First the thermostat was replaced to fix the problem so its highly unlikely that that is the problem. Yes the cap is suspect and will be replaced next, however the intermittant thing just dosen't seem so simple (I hope so and will do it). Next I assume the consensus is that the heater valve is ruled out as a culprit so Finally what and where is the monovalve and can it cause these sorts of symptoms??
Thanks again in advance
Alex

Very common problem with old 300es is a loose cylinder head.This will cause the problems that you discribed as the compression pressure leaking will force the water out past the radiator cap.The car should run at 90 degrees centigrade. Have a mechanic retorque the head cold to 60 foot pounds.Usually this will fix the problem. Otherwise a headgasket replacement is called for.
Check/replace radiator cap .You are probably pumping the water out so that car is always low on water.