I have seen a few threads about similar problems but haven't seen any comments saying they fixed it.

I have a 1998 2.5L Ranger (The Lima one). It was taking a long time for the temp gauge to raise to normal temp, I suspected a stuck thermostat and replaced it.

Now the gauge only raises when the engine is revving. It drops at idle speed.

My question is: Should I change the radiator, the water pump, or both? Or is it a temp sending issue? Has anyone else solved this issue in their Ranger?

 

I had a similar issue with my temp gauge. It needle would only go up a little bit. It turned out to be the temp sensor that is situated in the water outlet( I think it is called that...where the thermostat goes in). The sensor was actually broke in half with only one of the two wires intact.
I really do not think that changing the radiator and water pump would solve your problem.
Good luck

 

Yes, +1 ^^^

Change temp SENDER first.

Fuel injected engines have 2 temp sensing devices
ECT(engine coolant temp) SENSOR, only used by the computer
ECT SENDER, only used by the dash board gauge.

I believe the ECT sensor is on the side of the 2.3l/2.5l engines, drivers side front on or near the head under intake.
This is NOT the one you want to change.

Auto parts guys often think they are the same, so make sure you are getting a SENDER not a sensor

 

I ordered a sender from rock auto. On the Lima engine, if I am correct, the sender and sensor are right next to each other on the thermostat housing. Is that correct? The wires were intact but I will swap it out and report the results.

 

Ok, replaced the sender, went ahead and replaced the rad hoses while I was at it. And back flushed the radiator since it was just 2 more bolts to pull it.

My gauge is still randomly dropping, though it's not bottoming out all the way like it was before. Only droping to the line above the "C". Before it would bottom all the way out .

From what I've deducted thus far, I have air in my system. I burped the system after I filled it and wat he'd the coolant drop and filled it back up. Waited for the gauge to climb back up and topped off. Then shut it down, and topped off again when it cooled.

Do I assume residual air pockets or just swap the pump? It is a 1998, has 135000 miles and the pump is original.

 

The thermostat should be a 192/195 degF
A thermostat starts to open at its rated temp, so when coolant in the engine is at 190degF t-stat will start to open, when the colder coolant from rad starts to come in t-stat will close until that coolant is warmed up to 190degF, and so it goes until there is an equilibrium reached between the 190degF coolant leaving the engine at the upper hose and the 15deg cooler coolant coming in from the lower hose.
So thermostat may only be open 20% on a cold day vs 100% on a hot day.
But temp gauge should be very stable because thermostat is not an full open or full closed device, it adjusts flow/cooling. so no big swings in the temp needle.

Not sure how a waterpump could cause what you describe, if the impeller blades were worn down so limited circulation at low RPMs then t-stat would be open all the way.
As you raise RPMs flow/cooling would increase so temp gauge would start to go down but t-stat would also start to close to maintain the 190degF.

At sustained higher RPMs after gauge drops, does the temp gauge come back up to "normal" level, 190degF, or does it stay lower?

Remove heater hose at firewall, fill system until coolant comes out the hose/fitting.
Reattach hose.
Leave rad cap off and start engine.
Top it up as needed.
If should take 5 to 8 minutes before thermostat opens and upper rad hose and rad coolant starts to warm up.
It may burp some more air at that time, top it up.

Put rad cap on.
Mark, with tape, the coolant level in the overflow tank.
Drive it and if possible go up some longer grades/hills, that heats up the cylinders and coolant, and should cause higher pressure in the system sending coolant to overflow tank.
When you get back home check the level, should be higher, but may have burped out some more air so maybe not, mark the new level, don't remove old level mark.
Let engine cool down, as coolant cools off it shrinks and will suck coolant back into rad from overflow tank.
After a few hours check level again, coolant level should be lower, if not check overflow hose for leaks, and replace rad cap.

When engine is cold remove rad cap and coolant should be at the very very top, no air at all.

 

It does climb back up when I rev the engine. The last few drives it has been finding a resting place in the middle of the gauge with little to no moving. So it could be the equilibrium you were talking about. I had an engine with a bad impeller and a very small leak that was doing similar things.

I have not noticed any signs of leaking. The coolant level has stabilized when cold and relaxes to the same level in the tank and radiator.

The timing belt is due (starting to crack) so I figured I might as well just do it all in one shot since the kit with the water pump is cheaper than the timing belt and tensioner separately.

 

Don't know about the 2.3 (I'm new) but I've had several Pontiac Bonnevilles with the 3.8 liter Series II V6, and they are notoriously hard to refill.

The solution with them was to drill a 1/16" hole in the thermostat border so air could bleed out past the thermostat. Not big enough to flow a lot of coolant, but over several drives the air bleeds out. Fill the cooland bottle to the top and monitor it to watch it work. Can't hurt.

Where the hell IS the thermostat housing on the 2.3, up under the coils somewhere? I was gonna flush my radiator and haven't figured out how to get in there to pull it out yet.

 

I wouldn't advise doing any drilling into those housings. Cooling systems work under pressure. Along with the actual antifreeze raising the boiling point of water, so does the pressure that the cooling system creates.
Not only that, but you're basically putting out an invitation for dirt to come inside your engine, which will damage parts over time.

Just follow the upper radiator hose until it reaches some point where it attaches to the block, and you'll find the thermostat.

As far as belching the system of air, if the 2.3 has a radiator cap, stick a snug-fitting funnel (bonus points if you have a spill-free funnel) and give the engine a good rev a couple of times. The water pump will force in more coolant and displace the air out of the system.

If it doesn't have a radiator cap, fill the resivour tank to the full mark and again give the engine a good couple revs. Same thing happens, just a different way to skin the cat. If you go out for a drive, I'd recommend bringing an extra jug of 50/50 with you, if a massive air bubble works its way out, then the system drinks up what coolant was in the resivour.

Another tip, if your Ranger is equipped with a heater, roll all your windows down, turn the heat on high and vent it out the windows. Doing so will allow the heater control valve to open, allowing more flow and also removing any air that may be in the heater core's lines.

Something else to look into, is the water pump may or may not have a bleeder on it. Some do, some don't. I can't say for sure one way or the other.

One other thing to try, with the engine running and heater on, massage the upper radiator hose, wearing gloves if hot. Air likes to stay near the top of the system. Doing this, even if air isn't necessarily in the upper radiator hose, can still move the coolant around a bit and help to work it out of other areas.

Of course though, don't open the system while hot. You'll get scalded.

 

Ron: the small drill hole goes into the THERMOSTAT ITSELF, not the housing.

 

Thanks for the compliment but, I'm not Ron lol. All the same though, I still wouldn't do any drilling into those components.

If you're worried about flow, ditch the old thermostat and buy a new one.

 

Whoops, sorry.

More coffee needed.

ETA: it's not for flow, it's to allow air to escape and get a good fill.

 

If you want air to escape during your filling process, buy one of those cheapie flush/fill kits. You can find 'em for 5 bucks or less nearly anywhere.

Take one of the T fittings and pick a spot on the heater core hoses. Either sub out the heater control valve like I did, or cut a section of the tube and put that in it's place with the hose clamps. While you're filling, take the cap off of the T fitting, and that will allow air to escape.
I'd recommend subbing out the heater control valve, and plugging up the vacuum line with a golf T. Doing it this way means you get full flow through the heater core all the time, which helps to prevent gunk and whatnot. It also doesn't affect your AC, thanks to the blend door. Another bonus of putting a T fitting at the top of the system, is the water from your garden hose will then run down through the entire system. Works wonderfully I might add.