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Car runs hotter after new radiator, thermostat, and burping!


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I just replaced the original radiator on my 02 with a 320i. The car now runs very hot just idling in the driveway based on my VDO temperature gauge and after being burped. (Front on jacks, running with rad cap off until coolant is filled/topped off). I had to trim the fan blades a bit, not sure if this affected it?

I replaced the thermostat with a 75* and tested it prior to installing. Before the thermostat is even open, the car is in the mid 200*'s, full red.

I am thinking maybe there is a bad ground or bad sensor unit for the VDO guage? I replaced the connector on the unit as you can see with the blue connector.(stock gauge does not work)

The picture below, I can't seem to figure where the electrical connection goes, the temperature sensor wire is within this bundle. It looks to be a set of grounds?


Could my problem be a bad sensor unit/ground/gauge issue?

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Merry Christmas !

now -

it was running hot before 'repairs' - yes?

radiator didn't fix that ?

thermostat didn't either ?

swear no air trapped? and you have FULL HOT heater output??

can it be your really working around a cracked cylinder head?

failed head gasket?? water pump and housing condition? age?

erroded inside housing?

sorry you showed us your 'trimed fan' - that really is sheit now

so order a new 'tropic' blade for when the other issue is cured

'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

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you can't have a vdo and stock gauge on same sender. must have separate senders for each. with only your stock one connected, what does it say?

does the sender range match the vdo gauge?

using an IR gun (CHEAP at auto and hardware stores, everyone should have one) measure temp and compare to gauge readings.


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Guest Anonymous

Sam 99 % of my overheating problems came from air trapped in head, there is a bleeder screw in the block under the exhaust manifold between 3 & 4, with motor idling lossen the bolt to release air trapped in head, a real nasty job but it is per BMW plan, to avoid getting air trapped use syphon method of filling radiator, take a 18 inch piece a vacum line and syphon your antifreeze into radiator, its slow but allows head to burp itself, since 1999 I have used this method with nary a overheat problem, all stock parts.

Dave Miller

Merry Christmas all

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use a mechanical thermometer to check coolant temperature in the radiator.

And if you're using the original VDO temp sender on an aftermarket VDO gauge, are you sure the two are compatible?

That sender grounds through its threads--are the threads on the sender and its threaded socket both nice and clean?

Finally, are you really sure the system has all air purged? Didja refill with the heater set to full hot? Did you loosen a heater hose (outlet side on car's left/driver's side) to make sure there's no air trapped in the heater core?

Let us know whatcha find...


'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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You said you installed a 320i radiator. Was it a new or a used one?

A colder thermostat will not make an engine run colder if the radiator has a problem getting rid of the heat due to plugged tubes.

Do you see coolant flowing in the radiator?

Try burping it with the radiator cap on. Watch that fan when you do it.

No amount of skill or education will ever replace dumb luck
1971 2002 (much modified rocket),  1987 635CSI (beauty),  

2000 323i,  1996 Silverado Pickup (very useful)

Too many cars.

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Thanks for all the feedback and suggestions.

Before the new radiator, the car only ran hot on the highway pulling hard or up hill, would be a constant 180* otherwise.

The 320i radiator is brand new. Today I ran the car for a good 45 mins and it was pegged between 180-190* after messing with the gauge. All hoses could be touched by hand and the thermostat never seemed to open or at least the hose was not very hot. Even the upper hose was hot but still able to touch by hand.

Wanting to pick up a IR thermometer to do a full read, can my problem now be that car is not hot enough?

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