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Fluctuating tempature

Tiny
JJ58551
  • MEMBER
  • 1989 FORD BRONCO
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 118,000 MILES
What would cause the tempature of the engine to fluctuate pretty much the whole time your driving it? It's not over heating but gets close at times. Ive already changed the thermostat and sending unit.
Friday, February 25th, 2011 AT 1:55 PM

10 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
That usually means air pockets in the system, probably due to a leak somewhere. Have the system pressure tested.
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Friday, February 25th, 2011 AT 4:37 PM
Tiny
JUGGERNAUT615
  • MEMBER
  • 24 POSTS
Also check to see if the radiator is not cloged old radiators especialy ones who have been filled with tap water tend to rust from bottom up. Easily checked when car is cold start it up let it run for 2 minutes then shut it off. Then feel the radiator at the bottom then up towards the top it should be around the same temp but if bottom is cold and top is warm the bottom of the radiator is clogged with rust the only fix is to replace this cannott be fixed with flushes.
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Saturday, February 26th, 2011 AT 2:03 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
I don't agree with the previous answer.
First off, the radiator core is aluminum now and doesn't rust, second, it is normal for the bottom of the radiator to be cooler because that's how it works. The temp of the coolant lowers as it passes through the core to the bottom. Thirdly, that is not a symptom of a clogged radiator to act that way.

The temp is fluctuating because the sensor reads coolant and not air so if the sensor hits an air pocket, it reads cool, even if the engine is not.
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Saturday, February 26th, 2011 AT 2:12 AM
Tiny
JJ58551
  • MEMBER
  • 33 POSTS
I also want to ad that this happens mostly on a long grade or hill, when trying to keep speed. I looked it up on 2carpros and it said this is caused by clogged radiator. Is this a possibilty?
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Saturday, February 26th, 2011 AT 1:29 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
A clogged radiator will lead to gradual overheating but will not cause constant fluctuation in temp. Low coolant will do that.
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Saturday, February 26th, 2011 AT 1:31 PM
Tiny
JJ58551
  • MEMBER
  • 33 POSTS
Ok update on bornco. I have done everything. The radiator is new the thermostat is new and the sending unit is new. Still fluctuating tempature. What now? I have been told by a couple of diffrent people that the water pump could be the problem. Please does anybody have any idea?
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Tuesday, March 1st, 2011 AT 3:14 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
I told you that is wasn't the radiator in the first place.
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Tuesday, March 1st, 2011 AT 10:29 AM
Tiny
JJ58551
  • MEMBER
  • 33 POSTS
Syestem was checked and you are right it wasnt the radiator nor the thermostat. And there was no air pockets in the system. It is in the shop today getting a waterpump. This is the only thing left and if this dont fix it then im going to scream. Thanks wrenchtech for your help.
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Tuesday, March 1st, 2011 AT 5:00 PM
Tiny
JJ58551
  • MEMBER
  • 33 POSTS
Oh yeah everyone that answered, it has a head gasket.
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Wednesday, March 9th, 2011 AT 9:22 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
Yes, that causes coolant out and hot air in. The head gasket was probably the result of an earlier overheating so make sure you have found the original cause of the coolant loss that led to the head gasket failure.
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Wednesday, March 9th, 2011 AT 9:26 PM

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