Mechanics

735I COOLING SYSTEM

1973 BMW 740

Hi all and hope you can help. I bought a bmw 735i, England, last week. It has 86,000 miles with a V8 3.5ltr 5 speed steptronic gearbox. I bought the car and drove 50 miles home with no problem but the following day I had a 90 mile journey and 3 miles from my destination, m the temp gauge shot up and I pulled into a garage within 2 mins only to have the expansion tank lid blow off! Of course it was undriveable after that. It was taken back home and I drained the rest of the fluid and replaced the expansion tank. I turned on the heaters full and slowly topped up the tank to make sure that all the air was released and I could see the coolant dropping and bubbles coming up through. Once the engine had reached its normal running temperature and the coolant level was correct, I watched this and let the engine run for half an hour and replaced the cap. I then went out for a drive and after about 40 miles the heater stopped working and only cold air came through. I got back home and waited for the engine to cool and then topped it up again. Where is this coolant going and why? I can`t find any leaks but you can smell coolant in the car cabin after a while. The thermostat is operating and so is the waterpump but I can`t locate the problem. Any ideas? Thanks and look forward to your help.
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Maxmoves64
November 21, 2007.




Has a cooling system pressure test been performed? Also what is the production date of the vehicle(open the drivers door and look for the sticker on the " B" pillar) The V-8 motors have a tendency to leak at the valley pan (under the intake manifold) at the mileage you quoted. There are quite a few age and mileage related issues that go along with ownership of the V-8 motored BMW automobiles. Cooling systems that utilize plastic require periodic replacement of components, as you have seen.

Dr. Hagerty
Nov 21, 2007.


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