1986 325es radiator overheats in traffic

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bmwuser8@gmail.com - 12 Oct 2007 20:36 GMT

Hello All, happy Friday!
My 1986 BMW 325es runs hotter in traffice and when I am on highway (or
motorway for you Europeans!) it cools down a little bit.

The car has 215k miles on it and eversince I put a performance chip in
it (bought it online) it runs great (have to use 91 octan fuel though)
and I do get aroung 26MPG on highway.

When I am driving in traffice the gage shows it is at 1/2 marker point
but on highway it moves down a little bit and stays in between 1/4 and
1/2.

I just drained the coolant and put new antifreez in the car thinking
that it might help but it did not.
Could it be the thermostat?
The fan blades look normal and raditor does not leak at all.

The car runs fine even in traffice but I do get the antifreez
overheating smell that you usually sense when cars overheat. Smell is
obviously stronger when you open the hood.

Any ideas anybody?

Thanks in advance.

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Scott Dorsey - 12 Oct 2007 23:25 GMT

>I just drained the coolant and put new antifreez in the car thinking
>that it might help but it did not.
>Could it be the thermostat?

Yes, it could be.

>The fan blades look normal and raditor does not leak at all.

Does the fan feel stiff when you turn it? A common failure is that the
fluid clutch on the fan will fail and become loose, so the fan does not
turn at the proper speed when the engine is hot.

Don't forget to pressure-test the radiator cap.

>The car runs fine even in traffice but I do get the antifreez
>overheating smell that you usually sense when cars overheat. Smell is
>obviously stronger when you open the hood.
>
>Any ideas anybody?

Could be anything, but check the fan clutch, replace the radiator, and
test or replace the radiator cap before you swap out the radiator or pump.
There isn't much else to go wrong.

If you pull out one of the sensors and you see a layer of mineral buildup
on it, you may want to consider doing an acid flush on the system too. Note
that when you do the acid flush, anything that is a little leaky is going to
turn into something very leaky almost immediately, so be prepared to do some
replacement if you risk the flush.
--scott

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"C'est un Nagra. C'est suisse, et tres, tres precis."

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Jeff Strickland - 12 Oct 2007 23:55 GMT

You have described the exact problem that arises from having a worn out fan
clutch.

While in traffic, the air flow through the radiator slows, and the temp
rises. The fan clutch (viscous coupler) heats, the viscous material (a sort
of jell-like material) expands and causes the clutch to lock, which
physically attaches the fan directly to the water pump pulley which is
driven by a fan belt. The result is that the fan draws air through the
radiator to bring the heat down.

When the clutch fails, the fan never locks to the water pump pulley, and the
result is insufficient air flow and an associated heat rise. when the
vehicle speed increases, cold air is forced through the radiator, cooling
the viscous material, releasing the fan from the pulley and freeing up a bit
of horsepower and reducing noise at the same time.

Your fan clutch is toast. You can buy one from the auto parts store, the
price range is rather broad, and you can expect the price to be $100ish. It
is not difficult to replace.

> Hello All, happy Friday!
> My 1986 BMW 325es runs hotter in traffice and when I am on highway (or
[quoted text clipped - 20 lines]
>
> Thanks in advance.

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Dan Buchan - 13 Oct 2007 19:30 GMT

> When I am driving in traffice the gage shows it is at 1/2 marker point
> but on highway it moves down a little bit and stays in between 1/4 and
> 1/2.

Sounds like it's underheating not overheating. BMWs sit at halfway on
the gauge and don't budge once they're warmed up.

It probably is your thermostat - sticking open. When you're moving
faster there is too much airflow cooling the radiator and the thermostat
should be closing to compensate, but isn't.

That's if your temperature gauge is working properly.

Dan

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