Cooling system problem in 1979 BMW 320i

[Alan]

Hi gang,

My bimmer lately has begain to clinb up towards the high end of the temp gauge and now is going to the red zone after about 25 minutes of driving.

One of the things I noticed is that the hose leading to the bottom of the radiator from the thermostat housing is always cool.It's an old part so I got a new one,installed it,still acting the same way.Wasn't like this during the summer, the cooling system was running fine according to the temp gauge.
(BTW,I recently changed all the coolant with fresh stuff.)

The outside temperature where I am is has been around 40 and below recently(today was in the 20's)and it's pegging out the needle but the lower hose remains cold(it's a 75c stat).

Could it be that's been cool enough outside that the coolant never gets hot enough to open the stat(the engine bay gets good air flow around the motor)or is the new stat a dud?

What's the best way to test a stat?

 

[sbc350gearhead]

Is your fan electric? Is it working properly? Do you have any cooling leaks? How old is your water pump? Do you have any air trapped in the cooling system when you changed coolant?

 

[Titanium_Alloy]

Most likely it's the stuck thermostat. When was the last time you replaced it (if ever)? Replace thermostat and gasket and see if everything goes back to normal.

Regards,

 

[Alan]

I tested out the old stat and it opened right up with boiling water poured into it.

The stat is housed in a metal enclosure with the hoses from the block,water pump and lower radiator hose connecting to it.It gets a lot of outside air flow around the metal enclosure surrounding the thermostat.

The fan runs off a belt.

I'm assuming the new stat I installed works fine but the problem remains.The water pump has a cast impeller so I think(hope)it's still working fine.There aren't any leaks from the cooling system.

The lower hose feeding the radiator remains cool.If there is air in the cooling system,what is the best way to purge it out?

 

[JohnnyO]

Put the cap on only halfway and drive around for a while. It will heat up more with a little pressure but the air will boil off easier with the cap not on all the way. Put the heater on too when you do it. The lower rad hose comes from off the thermostat? I'll confess I'm not real familiar with many imports. No disrespect, but make sure the t-stat is facing the right direction too. Also if the heater is pumping out good hot air when it's supposed to, then it's probably okay.

[ January 08, 2004, 11:01 AM: Message edited by: JohnnyO ]

 

[Ray Garlington]

quote:

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My bimmer lately has begain to clinb up towards the high end of the temp gauge and now is going to the red zone after about 25 minutes of driving.

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Make sure your temperature guage is working properly. If the guage is ok and it is indicating in the red zone, the engine will be quite hot. Coolant will probably be boiling or close to it.

So, if your engine doesn't seem too hot, it probably is the guage malfunctioning.

 

[Alan]

The thermostat is idiot proof as far as the direction it can be installed.I'm gonna try the loosened cap idea.

I'm starting to suspect something electrical also.When the headlights are switched on the temp gauge always jump up a bit,turned them off and it goes back that tad.Maybe a bad ground connection?

 

[thrace]

The problem could still be the thermostat. Had a 320i which overheated. My engine was hot. Not just the gauge. It had that overheating engine smell and it gave off alot more heat when opening the hood and checking the engine. Changed the thermostat and flushed the cooling system using a prestone flushing tee. Ran even hotter after. I did test the stat in boiling water and it did open. Then I ran it with just a copper tube in place of the thermostat. It ran too cold always. Years later, I did change the thermostat again and the temps were normal afterward. Both replacements were from the BMW dealer.

[ January 14, 2004, 12:43 AM: Message edited by: thrace ]

 

[The_Jeff]

Could be a bad ground in the intstrument panel or a gauge voltage regulator if you have one. Air-burping with the cap loose is best done facing steeply uphill if your radiator is the tallest point in the system. Do you have a surge tank (pressurized) that's higher or an overflow tank (nonpressurized)? Look around the top of your engine for plugs you could take out for air burping. Thermostats are what auto parts makers practice on before they get good at things, or so it seems; keep trying heavy duty brands until you find one you like. If you get air in the system behind the thermostat it won't feel the heat from the coolant and open. So if all else fails drill a tiny hole, your smallest drill bit, in the flange of the thermostat to burp the air and let the water through. Mount the thermostat with said hole upright.

 

[Dr. T]

How come nobody's mentioning a clogged rad. When was the last time it was changed?

 

[Alan]

I just changed all coolant from the block and radiator.It's not clogged.

The system I'm starting to thinks is a heat sink system.The radiator is raised above engine so it seems to purge air from the system itself.Since the stat isn't getting hot enough to open the coolant goes to the top of the radiator where it is cool.I am really thinking the problem is electrical as there is no overheating smell,no rush of heat at all when I pop the hood.Matter of fact a lot of parts feel pretty cool for an engine thats been running for 45 minutes.

I took a temperature(infrared)reading of the stat's housing and got 165 F.I guess the coolant just isnt hot enough to open the stat keeping the lower radiator hose cool.