Engine Temperature LOW and Fluctuating

[lancer6x]

Hi guys I've spent hours scanning through the entirety of the internet to find someone with a similar problem, but no one seems to have this issue with these specific symptoms.

So for the duration I've owned my 99 3.0 ranger (4 months) my coolant gauge has always displayed that the engine was running cold. When the truck warms up the gauge needle will approach the C line, and then right after passing it begin to travel back down below it. It fluctuates like this continuously.

So I plugged her in to my ODB-II scanner, and the engine temperature it is reading is fluctuating between 180-190, going up and down and up and down, never going above. So it's not the gauge. And my fuel mileage has also been effected (getting under 13 highway).

So at this point I'm sure you will say this is just like a lot of threads and I need to do my research, but here is where things change. My heat works. It works great! Like it blasts heat like crazy. No clogs in my heater core. But the temperature of the engine is also not noticeably effected by me running my heat either.

I have flushed the coolant, I have changed the thermostat, I have parked on an incline and ran it for a while with the radiator cap off to try to coax air bubbles out, but my truck continues to run cold. I can not figure out what could be causing this. I would really like the better performance and fuel economy associated with the car running within its optimal temperature zone, and this issue has been driving my nuts.

Any help is appreciated!

 

[RonD]

Computer(obdII) uses a 2 wire ECT sensor to get engine temp.
Dashboard gauge uses a 1 wire sender to get engine temp.

For both to be reacting as described then coolant temp is indeed fluctuating, so not an instrument issue.
180-190degF is odd though, that is below t-stat opening temp, was the upper rad hose warm?
i.e. was coolant circulating to the rad.

Thermostat should be a 192 or 195degF, not a 180degF, just FYI, and not related to problem, but will effect MPG if 180 is used.
Optimum operating coolant temp is 200degF to 215degF, this is usually just below 1/2 on Ford gauges, 1/2 is usually 220degF

If possible I would see if OBDII temp was/is fluctuating during warm up, i.e. prior to t-stat opening and Radiator becoming part of the system.

Not sure on a '99 3.0l but Ford often used a By-pass on the heater control system, this would have 4 hose connections, and a valve.
If the valve plate gets loose it can cause temp to fluctuate, similar to partially blocked core, not sure if this would effect the heater temp enough to notice.

I believe the 3.0l also uses an intake pre-heater, 2 hoses "T"-ed off heater hoses that run to upper intake, I would remove these and see if that intake pass thru is partially blocked, or one of the hoses.

Just thought of this:
Check the Fan Clutch.
Start cold engine and let it run for about 1 minute, then shut it off.
Open the hood, spin the fan, it should spin freely and easily
If it is tight then you may have found the problem.

The Fan clutch operates by being heated by the Radiator, not the engine.
Fluid in the clutch is cold when engine is so will be thick, which is why you need to run engine for a minute before the test.
Most people notice this fan noise when first starting an engine and then it goes away after about 30sec to a minute, thats the fluid in the clutch warming up and thinning out to disengage the fan, and the fan noise then drops away.
On the front of the clutch(by rad) is a bi-metal spring, if it is warmed up it opens a valve to engage the fan more, warmer it gets the more it engages.
Usual failure for a fan clutch is when it doesn't engage the fan, this is seen as rising engine temp when idling at a stop light, and then return to normal temp when driving, air is passing thru rad again while moving.
But they can fail in engaged position so they are over cooling the system, the fan it self is circulating air over the engine cooling it and also pulling more air thru the rad than needed.

Your fluctuation was the t-stat reacting at its open/close point(190degF), and new t-stat would do the same.

 

[lancer6x]

The Fan clutch operates by being heated by the Radiator, not the engine.
Fluid in the clutch is cold when engine is so will be thick, which is why you need to run engine for a minute before the test.
Most people notice this fan noise when first starting an engine and then it goes away after about 30sec to a minute, thats the fluid in the clutch warming up and thinning out to disengage the fan, and the fan noise then drops away.
On the front of the clutch(by rad) is a bi-metal spring, if it is warmed up it opens a valve to engage the fan more, warmer it gets the more it engages.
Usual failure for a fan clutch is when it doesn't engage the fan, this is seen as rising engine temp when idling at a stop light, and then return to normal temp when driving, air is passing thru rad again while moving.
But they can fail in engaged position so they are over cooling the system, the fan it self is circulating air over the engine cooling it and also pulling more air thru the rad than needed.

Did a test last night. Before leaving work and starting the car (sat cold for several hours) I popped the hook and spun the fan. Felt a noticeable resistance which felt like the clutch spinning in viscous oil.

Then started the car and drove a mile to Benny's. At Benny's turned off, popped hook, and spun the fan. Felt exactly the same no change.

Bought some stuff at Benny's, and drove 6 miles home. Car warmed up to where it normally operates. At home, turned off, popped hood, spun fan again. Still felt exactly the same.

so tl;dr: fan exhibits same resistance to hand motion regardless of whether car is cold, just beginning to warm up, or warm from a normal drive.

 

[RonD]

At Benny's the fan should have been spinning freely, 1 to 1.5 full turns after you spin it.

If you have another vehicle or a friend does, try the test on that vehicle, so you can get the general idea of what to expect from a working fan clutch.

But it reads like it is not disengaging fully so air is constantly being pulled thru rad and over engine

 

[nich94]

Hi
I am having the same problem. I have a 1993 ranger with a 4.0. Just replaced my water pump, sensors, radiotor, thurmastate, fan, clutch fan and hoses. Truck will warm up just fine and drive for about 5 minutes with no problems. the readings after about 5 minutes is it starts to rise to about to the L then fall below N very quickly. I have tried everything I'm completely lost on what to do next. would the heater core have anything to do? I found no clogged ports, what about my fan clutch or fan they seem a little different from the stock one I bought at napa. Any help would be great
thanks Nick

 

[RonD]

On my '94 4.0l the temp gauge would fluctuate randomly, after warm up, from below half to above half.
It was the heater core, very easy to change on mine, $28 for new core, and about 30min. job the first time

 

[jco77on]

When the truck warms up the gauge needle will approach the C line, and then right after passing it begin to travel back down below it. It fluctuates like this continuously.

My heat works. It works great! Like it blasts heat like crazy. No clogs in my heater core. But the temperature of the engine is also not noticeably effected by me running my heat either.

I have flushed the coolant, I have changed the thermostat, I have parked on an incline and ran it for a while with the radiator cap off to try to coax air bubbles out, but my truck continues to run cold. I can not figure out what could be causing this. I would really like the better performance and fuel economy associated with the car running within its optimal temperature zone, and this issue has been driving my nuts.

I have the exact same issue with my '89. My heat gauge seems to run slightly warmer than yours, but nowhere near the middle of the gauge. More like the N on "normal" label. And also having that fluctuating. And the heat working threw me for a loop also.

 

[jco77on]

I suspected my fan clutch was bad, after warming to operating temp I would get maybe 1/4 turn on the fan after shutting down. The new fan clutch seems to get about 1/2 a rotation after being warmed up, and replacing this had no effect on the engine temp gauge reading very low.

 

[RonD]

I suspected my fan clutch was bad, after warming to operating temp I would get maybe 1/4 turn on the fan after shutting down. The new fan clutch seems to get about 1/2 a rotation after being warmed up, and replacing this had no effect on the engine temp gauge reading very low.

Minimum operating temp is set by the thermostat, Ford uses 192 or 195degF t-stats.

If temp gauge or it's sender is not the issue then low operating temp would be thermostat problem, it is not closing all the way.

Thermostat is on the engine end of the upper Radiator hose.
To see if thermostat is the problem start cold engine, feel upper hose near rad end, it will of course be cold.
Let engine idle for a few minutes and feel hose again, if it is warming up with the engine then thermostat is bad, i.e. stuck open.
It would normally take 5 to 10minutes for engine to warm up coolant in the block and heads to 190degF and then thermostat would start to open a bit, and upper hose would get warmer, as the cold coolant from rad comes into the engine from bottom hose it will cool down the thermostat and it will close until new coolant is warmed up to 190degF and it opens again, this continues until all the coolant is warmed up.
On very cold days thermostat may not open much at all.

Fan clutch not engaging all the way causes temp gauge to go up when at a stop light and then temp goes down to "normal" when moving again.
Radiator requires air flowing thru it to cool down coolant, if fan isn't pulling enough air thru rad when stopped then temp rises, when moving the air flow returns and temp drops.

Fan clutch always engaged, first makes a noise, we often notice this noise when starting a cold engine, loud fan noise that goes away after a few seconds, that's the fan clutch locked because fluid inside is cold, once it starts spinning fluid warms and releases clutch, it is now disengaged and noise goes away.
Fan engaged all the time wouldn't lower engine temp, thermostat would just stay barely open to maintain 190-200degF engine temp.