temp fluctuations

[nich94]

Hi
I have a 1993 ford ranger 4.0. I just replaced my water pump, fan, clutch fan, radiotor, hoses, sensors ,and thurmastate.
My truck warms up fine but after 10 minutes it heats up the letter L and then falls below N right after words. This continues to do this throw out the drive.There head gasket is not leaking into the oil or outside. I'm completely lost on what to do next with it. Does the heater core have anything to do with it? Fan clutch being bad? Spark plugs ? Any help would be awesome this drives me crazy that I cannot find out what it is !!

 

[RonD]

Bad fan clutch will cause engine temp to rise while you are stopped(fan is not pulling air thru rad), when you start moving again air starts to flow thru rad and temp drops.
Missing fan shroud can cause similar symptoms

Heater core on some models is part of the coolant by-pass system, if it starts to clog up you can get random fluctuations on the temp gauge, there is no correlation between speed or if stopped, going uphill or downhill doesn't matter.
If this seems to fit then yes, for $30 and 30minutes you can have a new heater core.

Look at your heater hoses, if they go from the intake and water pump directly to the firewall/core, with no heat control valve seen, then yes your model is using the heater core as part of the by-pass system and a partially blocked core can cause temp to rise and fall.
You can try Back Flushing the heater core, but if it works at all it would be a temp fix at best, the $30/30min. is best.
Back flushing is good to do every few years when you change the coolant.

 

[86bronco2owner]

same here

i Have an 86 bronco 2 xlt and my temp gauge and sensor were acting up, but had a bad wire connection somewhere

 

[nich94]

Thanks for the replies I'm gunna try the heater core i checked all wiring and dont see any frayed wires. The clutch fan is new as well. Also what does it mean if you have a little whitened spark plug, is it bad or just needs replacing I haven't replaced them in a while?
Thanks I will keep this post going to see if it works or not.

 

[kimcrwbr1]

A good leakdown test will tell you if it is head gasket/s. Have you replaced the radiator cap? Maybe try running it with the radiator cap loose and see if the temp holds steady once the engine is up to normal temp. If you see steady bubbles out the radiator it needs head gaskets. If your heater gets good and hot it is not the heater core.

 

[nich94]

I changed the heater core and small difference not much. I'm lost with it. How can you look for head gasket problems?
Also how about shorts in the wiring ? Where to look for them ?
Thanks for all the help much appreciated.