Engine won't maintain temperature (too cold)

[It'sStillRunning]

I'm no stranger to a stuck thermostat. I've changed one in the past soon after purchasing my truck because the engine would not heat up. As this current winter settled in I noticed the same problem. Naturally I thought the thermostat was stuck so I checked and sure enough it was. The problem is that, even though I've replaced it, the temperature will not stay warm. The gauge goes up to the middle (what I assume is the opening temperature for the thermostat which is 192 on this one) and then drops back down to C. I'm on my second brand new thermostat and the problem persists. My dad suggested it is the fan clutch so I just got a new one.

I realize I should have asked before but I'm stubborn and try to solve problems myself before asking for help. I read how a thermal fan clutch works and from what I understand it's supposed to "slip" when engine bay temperature is cool (controlled by the spring on the front) and engage when it's warmer in order to maintain proper temperature. What I observed is that even at idle the fan is going full speed in <20F degree weather. It doesn't seem to slip at all. Am I way off here or does it sound reasonable? The engine is less than 2 years old with about 14k miles on it. It got a brand new water pump before installation and a failsafe thermostat (which failed as I said). I checked the fluid levels, added antifreeze and water to top it off, checked for leaks and nothing sticks out in my mind. I'll be installing the new clutch in any case but I'd welcome any thoughts from the community.

 

[Kowboy]

The clutch fan isn't exactly cheap to replace for precaution, $85 or so. When it goes bad it will let you know as you can hear it. It is a roaring kind of sound, not a rattle or squeal. To test it, you should be able to turn it by hand w/ some resistance. I recently replaced mine and think that I wasted my money. Manufacturers, want it replaced like around 100 K. The blade will always be spinning if the engine is running.

 

[wildbill23c]

My grandfather's 93 Ranger 4.0L was the same way, would never get very warm heat luke warm at best, and cold. Never did figure out what caused it, and after the POS transmission failed again on it the truck was sold for scrap.

 

[RonD]

The fan clutch is engaged by the temperature of the radiator, bi-metal spring on the front is warmed up by air passing thru the radiator, after t-stat opens and rad warms up.

It reads like your t-stat is not closing again, which it should, when the cold coolant in the rad flows in after t-stat opens the first time.
A Vehicles cooling system must be designed to cool engine to below 230degF even when outside temp is 100+degF, so there is more cooling power than needed for cooler outside temps, which is were the t-stat comes in, it must react in approximately a 10deg window, if the 4.0l's case that would be 190-200degF, if t-stat just opens at 192degF and then doesn't close again until 100degF it is useless in cold weather.

The fact that the temp gauge goes up to about 1/2 way means the engine is generating enough heat to warm up the coolant to 200degF, which is minimum operating temp for best MPG and lubrication.
When t-stat opens, warm coolant flows into upper rad and cold coolant now flows from lower rad to water pump and then to block and heads.
When this cooler coolant flows to t-stat it should close all the way or partially to maintain the 200degF.
It reads like your t-stat is not reacting this way.

On my 4.0l I often see the t-stat opening and closing a few times on very cold days, gauge drops a bit then comes back up 2 or 3 times, never drops to Cold though.

Make sure you got a 192 or 195degF t-stat, some use 180degF which would be wrong for the 4.0l's cooling system.
If you have an old t-stat you can check it in a pan of boiling water, water boils at approx. 212degF t-stat should be open all the way, turn off the heat and watch to make sure t-stat valve closes slowly as water cools, you can add cold water to speed up the process, but watch that valve doesn't snap shut, that's the sign of a cheap t-stat.
It will open then not close again until temp drops quite a bit, which is kind of what you are describing.

Good 192 t-stat will open partially at 190degF then be fully open by 200degF, and then close a bit when cooled, no snapping or sudden movements.

I have read that some 4.0l owners remove the fan clutch in winter months, but these owners were in locations that were in the minus temps day and night for the whole winter, some switched to electric fans.

 

[It'sStillRunning]

The fan clutch is engaged by the temperature of the radiator, bi-metal spring on the front is warmed up by air passing thru the radiator, after t-stat opens and rad warms up.

It reads like your t-stat is not closing again, which it should, when the cold coolant in the rad flows in after t-stat opens the first time.
A Vehicles cooling system must be designed to cool engine to below 230degF even when outside temp is 100+degF, so there is more cooling power than needed for cooler outside temps, which is were the t-stat comes in, it must react in approximately a 10deg window, if the 4.0l's case that would be 190-200degF, if t-stat just opens at 192degF and then doesn't close again until 100degF it is useless in cold weather.

The fact that the temp gauge goes up to about 1/2 way means the engine is generating enough heat to warm up the coolant to 200degF, which is minimum operating temp for best MPG and lubrication.
When t-stat opens, warm coolant flows into upper rad and cold coolant now flows from lower rad to water pump and then to block and heads.
When this cooler coolant flows to t-stat it should close all the way or partially to maintain the 200degF.
It reads like your t-stat is not reacting this way.

On my 4.0l I often see the t-stat opening and closing a few times on very cold days, gauge drops a bit then comes back up 2 or 3 times, never drops to Cold though.

Make sure you got a 192 or 195degF t-stat, some use 180degF which would be wrong for the 4.0l's cooling system.
If you have an old t-stat you can check it in a pan of boiling water, water boils at approx. 212degF t-stat should be open all the way, turn off the heat and watch to make sure t-stat valve closes slowly as water cools, you can add cold water to speed up the process, but watch that valve doesn't snap shut, that's the sign of a cheap t-stat.
It will open then not close again until temp drops quite a bit, which is kind of what you are describing.

Good 192 t-stat will open partially at 190degF then be fully open by 200degF, and then close a bit when cooled, no snapping or sudden movements.

I have read that some 4.0l owners remove the fan clutch in winter months, but these owners were in locations that were in the minus temps day and night for the whole winter, some switched to electric fans.

I checked the thermostats when I bought them. The first one said 195 stamped on the back, this one said 192 stamped on the back. I agree that's what it sounds like is happening. It opens up and stays open too long. The fan clutch change made no difference so now I'm not sure what to do.

 

[It'sStillRunning]

Ok, I tried what you said. I took the previous new thermostat, a 195 degree stant, put it in a pot and boiled it. It opened, I turned off the heat and stood there the entire time watching it until It closed. It closed smoothly just like you said. I also tried twice after that, boiled it and quickly put it in cold tap water and it closed as soon as the cold water hit it.

I sat and thought about it about, what you were describing. When the thermostat is closed no water is circulating so the water in the block heats up and the water in the radiator stays frigid. When the thermostat opens, the hot water exits and is replaced by frigid water. It seems like the temperature difference is too great making the opening and closing intervals too long and the water in the radiator gets too cold before the thermostat opens again. I wonder if I drilled some holes in the thermostat to keep water circulating constantly, just a little bit, if that would even out the temperature between the water in the block and the radiator or just make it cold all the time. I can't think of anything else. The fan never stops spinning so there is always cold air flowing through the radiator. I even blocked it off partially and it made no difference. I can't think of anything else to do.

 

[adsm08]

The fan is going to spin to some degree whenever the engine is running. The real test is to grab it with the engine off and cold and try to turn it. It should spin freely and not try to drag the water pump along with it.

FWIW I am in PA as well, and I am having the exact same issue on both of my vehicles, which warm up and stay warm when it gets above 10.


You parenthetical in the title nailed the problem. It has been too cold this winter. About the only other thing you could try yet is to replace the rad cap. My Ranger did start holding it's temp a bit better when I replaced the old cap two weeks ago. Th BII's temp gauge was all over the place this morning.

 

[RonD]

Well the frigid water coming in should close the t-stat a bit, then as coolant behind t-stat warms up it will open a bit, this should just continue on and engine should be minimum temp 192deF, no matter what temp the rad is, that is the point of the t-stat, maintain minimum operating temp for best performance.

Now if your temp gauge never climbed above a 1/4, with working t-stat, I might say the engine simply can't generate enough heat(i.e. Lima engines), but yours got to normal range, t-stat opened and then temp dropped and couldn't climb back, which I find odd, engine can generate enough heat but then can't?

No, making holes in the t-stat plate would make it worse, if engine is struggling to warm up some of the rad coolant it would be worse off trying to heat up all of it.
I would be more inclined to put a restriction in the upper rad hose, so flow was less even with t-stat open.
Put a big pair of vise grips on it, lol, close that hose off completely then work up from there
Get yourself an 1.5" ball valve with hose fittings to restrict upper rad hose flow in the winter.

The radiator flow is to get rid of "excess heat", which you don't have alot of, if any, so engine is not harmed with no rad flow, that's what the t-stat does, blocks rad flow, so restricting the upper rad hose might just work in very cold weather, like a manually controlled t-stat.

 

[SenorNoob]

Wouldn't this be the perfect case for a cover over part of the radiator? You know the cloth/leather things people use on full-size trucks when it get really cold?

Just have to remember to take them off before you burn thing when it warms up.

Edit: There is another product idea. The manual thermostat. No more sticking!

 

[turbo2256b]

Suggest when testing a T stat in a pan of water or such a thermometer should be used too.
Also I found the NAPA Premium Tstats to be a lot better than the cheeper ones. Others I have tried gave up on me in a month or two. I have real gages in my hot rod and dually.

 

[It'sStillRunning]

I tried blocking off the radiator with a piece of peg board and taped off enough of the holes until it maintained temperature according to the gauge. What didn't make sense to me is that when I park it after driving it at temperature I can hear the coolant boiling in the reservoir which is coming from the radiator overflow. As a last resort I will try to get a good quality radiator cap. That is the only thing I haven't checked.

 

[alwaysFlOoReD]

Is your rad fluid [glycol] at the proper percentage? It needs to be checked every year and replaced every couple years. The glycol helps transfer heat when in the proper proportions. Also I use cardboard directly in front of the rad when extremely cold, covering up to 3/4 of the rad.

Richard

 

[RonD]

50/50 mix Coolant doesn't boil until 230degF at no pressure, that's about 1/2 on the temp gauge.
With 15psi rad cap the boiling point is 265degF, HOT on temp gauge

Not sure what you are hearing in the overflow tank, bubbling could be air trapped in the system.

 

[bobbywalter]

sounds like a potential cracked head or gasket maybe, hopefully its the cap bleeding off at 3 pounds or something less troublesome.


when you start it cold does the upper hose get hard instantly?



did i just say that?

 

[Caesar]

I have issues with my temp gauge always being between 1/4 to slightly under the 1/2 mark on my 98 Mazda B4000. Since buying the truck over the summer it has never been at the dead center of the temp gauge, always a tick below it.

Well this "issue" lead me to a discovery. My mechanic (also my father in law) and I were about to swap the thermostat and purge the air and we went through several thermostats and none of them fit. We eventually discovered that my 98 Mazda B4000 has a 99 Explorer 4.0L SOHC engine instead of the OHV. So my truck has the external thermostat housing with two sensors, and both are stuck in there pretty good. We replaced the thermostat and flushed the system and the temp guage did temporarily go to the 1/2 mark. But now with the low temps it is back down to nearly 1/4 mark.

So I know the motor swap only complicates this problem. I am still not 100% sure if my truck is running off the original ECU, or the Explorer ECU, although I believe it is the ladder. My truck uses a PATS key, so that is a pretty good indication that it has the SOHC ECU. I believe one sensor sends a signal to the ECU and the other to the temp gauge. I am contemplating changing the entire housing and switching to the updated click in sensors vs the screw in sensors that often leak and fail. I am beginning to wonder if the low temps are causing the ECU to run richer on these colder days and effect my gas mileage. It hasn't been great as of late, and although it is a 4.0L I would welcome better mileage.

So is this just a "Ranger thing" or is it one (or both) of my sensors, the thermostat, air trapped in the system, or just the abnormally low temps these last few weeks? Also can the motor swap have an effect on the dummy gauge on my instrument cluster? In other words does it use a different ohm resistance to display the temp? Or is it the same between the OHV and SOHC? Any insight would be appreciated.