Bouncing temp gauge

[Ilikemice]

Hi all,

Typical. I planned a road trip next week and thought I'd change the coolant this weekend ready for it... now every few mins my temp gauge goes from normal to 1/4 then move back up again. It never overheats but I'm concerned about the fluctuation.

After changing the fluid, I let the car idle for 15 mins or so facing uphill with the rad cap off and the fluid level didn't seem to move much but the temp gauge stayed perfectly in the middle. Then I drove it for 20 mins and the temp gauge went to normal but then every few minutes it will drop down to about 1/4 then move up to normal. When I got home and let it cool down the fluid was lower in the rad and so I topped it up another 3/4 of a litre.

The hoses seem alright and not soft or buckled, the lower hose stays cool.

Before the coolant change the needle would stay in the middle and not move while driving.

I've scoured the internet but I've not found a similar issue with a resolution! Although it's not overheating I don't really want to keep driving if it could be hiding a different issue!

Any ideas?

 

[janolsson]

My first thoughts are air lock based on the theory that the sender measures the locked air then gets some water that's cooler. When you burped the system did you have the heater on hot??

However the tstat can give symptoms like that. If you haven't changed the t stat since owning the car then that would be my first port of call (only use oe stat). Also check the viscous coupling on the fan.

 

[Ilikemice]

The heater was on full and hot air was coming through the vents. I haven't replaced the thermostat. Do you know where to find an OE one at short notice?

 

[janolsson]

The heater was on full and hot air was coming through the vents. I haven't replaced the thermostat. Do you know where to find an OE one at short notice?

Dealer got me one overnight. He said I needed to order the oring separately so I did and found the stat comes with one

 

[Ilikemice]

Thanks Jan. I'll give them a call!

 

[Ilikemice]

I've been reading up about it and it could need a bit more burping so I'll try it again tonight. I read it takes a fair few miles to purge itself of air. I take it the air lock would clear itself out after a while.

Is it still safe to drive? If it had air bubbles and there was a major problem it should still read as overheating on the temp gauge, right?

Edit: I called my local Ford dealership. They can't get thermostats in apparently since the vehicle is out of production!

 

[Ilikemice]

So I had the car idling jacked up, facing uphill, with the rad cap off for about an hour and noted some stuff down:

- The top rad pipe stays cool until the car gets to normal temp, at which point it gets hot = T-stat opening correctly

- Bottom pipe stays cool until after a fairly hard drive at which point it's very slightly warm.

- With the rad cap off, turning the heater on causes the fluid level to drop slightly. I topped it off at this point then put the rad cap on.

- The expansion tank still contains brand new coolant. No murky green crap from the system has made its way in there yet.

- I had to replace the lower rad hose clamp with a regular hose clamp. There's an ever so tiny leak coming from it.

- Squeezing the heater pipes I can feel some bubbling... I've no idea how to purge this as you can't tip the car far enough up to let it burp.

- The gauge dropping is at its worst when the car is just started and driven, regardless of the engine temp.

- I drove around for about an hour with the heater on full blast. It was very hot.

- I squeezed all the pipes I could find to try to get any air out. For the whole hour not one bubble came out.


I've ordered a coolant temp sensor, thermostat, and new lower rad hose.

The gauge is reading the actual engine temp, right? Not the flow out of the engine or whatever... At the moment it's at normal temp about 90% of the time which makes me think it's not life-threatening, and it has NEVER gone past normal when idling or driving.

 

[axle4x4]

hi ilikemice coolant probs a bit late in reading your thread but when i replaced my engine back in the car i refilled coolant to radiator level, expansion bottle roughley half way, radiator cap on car on level garage floor left it ticking over for about 1 hour checking expansion bottle only but often heater was on full sorted its self but i could have been lucky though. hope this might help