Question about BMW 735i

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My 735i1990 bmw is randomly overheating.the upper radiator hose is stiff and hot to touch but the lower radiator hose is cold what does this mean

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Water flows in the bottom, and out the top of your engine. If bottom is cold, not just cooler than the top, could be a plugged radiator or failed water pump.

thermostat typically stays closed til about 170 deg F to 185, to warm the engine. When it opens, top hose gets hot quick. Thermostat sounds fine to me.

Posted on Apr 25, 2015

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Hi Michelle
it sound like the thermostat is playing up, replace the thermostat and your BMW will be OK.

Posted on Apr 25, 2015

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  • BMW Master
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This sounds like a coolant flow problem. possible rad plugged or water pump problem.

Posted on Apr 24, 2015

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Posted on Jan 02, 2017

lancer721
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SOURCE: 1998 jeep grand cherokee cooling problem

Your thermostat is stuck closed. It needs to be changed right away. By the way the operating temp on that motor is 160 degrees so you are running hot you have just been lucky so far. Good Luck

Posted on Dec 01, 2008

Mustgo
  • 2359 Answers

SOURCE: 1991 honda accord is overheating. Installed new

When the car is completely cool,check the electric fan(s) for smooth rotation.

Clean/check/change the thermo sensor,contact and wire.

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Excavate air pocket in coolant system / check for head gasket leak

This test will kill two birds with one stone.

===

MAKE SURE THE COOLANT SYSTEM and ENGINE IS COLD!

RAN THIS TEST IN A WELL VENTILATED AREA ONLY!

You will spill some coolant during this air pocket purge test.......BE KIND TO THE ENVIRONMENT and ANIMAL please clean up after the test!

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Put the front end on a pair of ramp or park your car on a VERY STEEP HILL (radiator facing top of the hill) .

Top of the coolant reserve tank

Let it ran for 10-15 minutes.

Monitor for air pockets escaping from coolant reserve tank.

Small amount of bubbles is OK at 1-5 minute mark

After the thermostat open up (after 195 F warm up) at
5-12 minute mark or after high idle you should see less bubbles.

If you do not see any in rush of bubbles then your thermostat may be partially stuck or rusted badly inside the thermostat hosing.

Give the thermostat host few gentle taps.

If you see larger bubbles surfacing after 15 minutes then should do a hydrocarbon (HC) dye test to test for potential head gasket leak.

Let engine cold down and top off coolant reserve tank.

Start monitor for coolant lost

===

A coolant flush is require every 2 years or 24,000 miles.

I recommend the thermostat that has a relief pop-let to reduce the change of burst radiator and coolant hoses.

Make sure you get a new thermostat gasket,black RTV and fresh coolant for the job.

===
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Posted on Dec 05, 2009

  • 3 Answers

SOURCE: 1996 VW Passat VR6 is overheating

Thermostat is most likely. Try that first, then my next choice would be water pump. Good luck.

Posted on Mar 14, 2010

  • 271 Answers

SOURCE: car overheating, coolant in resevoir cold,

First-change the thermostat and bleed the system.If the problem is still there change the water pump.

Posted on May 15, 2010

  • 4088 Answers

SOURCE: top radiator hose hot and lower hose cold. car

Either the water pump has failed, the radiator core is plugged, or the lower hose has collapsed and blocking the flow of coolant. Hope this helps!

Posted on Oct 15, 2010

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The lower hose shouldn't be as hot as the top. If your not having overheat problems I wouldn't worry about it. If the radiator was clogged, it would overheat.

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That is normal, it will not get hot without the thermostat. The water cools in the radiator and falls to the bottom and the bottom hose is cold. This is what cools the engine and stops it from overheating.

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Hi,i,m a guest here .i have overheating problem with my toyota camery 92 v6...i got that my fan isn't working well , i changed it & the fan got better,,but it's not fixed yet & still i have...


How about the thermostat?

If your getting heat out the vents, the coolant is full, the upper hose is hot and the lower hose is cold that the t'stat is not opening.

If both the hoses are hot, the coolant is full, and you feel the fan pushing hot air than check the front of the radiator for debris build up. If there is no debris than the radiator could be plugged internally or the cooling fins may be severely rotted.

If the coolant is full, there is no heat out the vents and the upper hose is hot/lower hose is cold the water pump is not circulating enough coolant.

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My radiator on my 1994 toyota hilux sulf is over heating just sarted in last few days. Temperature gauge fluctuates when i turn air conditioning on.how do i fix this


First check if you have any leaks in the cooling system , then check if level is correct(radiator and expansion tank , check level when car is cold , never open radiator when it's hot).
Then verify operation of radiator fan , if it's electrical fan it should comes on when temp. goes over normal,
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If everything above is working properly , and it's still overheating , you may have bad water pump or head gasket.

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