My '94 Ranger had a problem for over a year. It's running temperature would go way outside the "normal" range on the temp gauge. Additionally, the heater wouldn't get hot in cold weather. I replaced hoses, thermostat, et cetera and had the mechanic look at it several times to no avail.

I finally took it in to him last summer and told him to change the water pump as that was the only part that hadn't been replaced. That did it. The pump was the original (and had almost 200K miles on it), and he said the impeller blades were all gone. "There was just a shaft spinning in the stream," he told me later. I didn't think this could happen, but he said the blades most likely broke in pieces and dissolved over time.

Now the engine temp stays in the zone between the cold end of the scale and the low end of the "normal" range. I also tried the heater in warmer weather and it blew me out of the cab! I took the truck back in for other work, and the mechanic told me the radiator coolant level was low and he added about a "teacup's worth" of coolant. After that the engine temp went way up past the normal range again. I popped the radiator cap and ran the engine from cold for about five minutes, thinking that perhaps there was air in the system, and about a teacup's worth of coolant eventually came back out of the radiator. Now the engine temp stays in the low end of the range again. I finally read in a Chilton's guide that the collant system is closed, and additional fluid should only be added into the overflow bottle. Coolant would be pulled in as needed. I added a bit to the bottle with no change in temps.

Now that it's cold out I've noticed that it takes a bit before the heater gets warm, and even then it's not toasty. I'm surmising that the engine running colder has something to do with that. Can an engine run "too cold," and if so, how? Should I ignore the Chilton's and put a bit more coolant directly into the radiator?

 

these engines do run cool. you can put cardboard over the radiator. I used 1/4 inch poster board my kids had and a bungy cord.(I bet everyone on this forum with the 2.3/2.5 puts it over there rad, I only use the motorcraft tstat. I dont think it matters that you fill the coolant thru the rad cap make sure the overflow tube is not clogged. maybe once you get it working good and coolant is filled maybe then dont take the cap off and give it a chance to get air in the system, just a thought. If you changed the heater hoses and you know they are not clogged you could try and back flush the core or just replace it for $25 and 30 min of work. make sure you get all the air out also. just some thoughts pick and choose what works for you .

 

Thanks for the input. I had the core replaced when we were trying to figure out the heater problem last Spring. Coincidentally, I tried flushing/cleaning the system twice (for good measure) before I found out the pump was missing its impeller. By that time I said the hell with it and didn't do it again. Perhaps next Spring...and I'll definitely do the cardboard trick for now.

 

my 94 when I was driving to work would give me a eng check light when I would drive into a cooler spot during the winter. It was 70 miles 1 way and I went from 2500 ft to around 4500 and when I would crose some of the hills the light illuminated, truck ran fine but I noted the cooler temp level. Put a paper bag in front of the rad and had no more problems. Had this situation for about 6 years. Now I guess the slipper fan is going but since I dont commute any more I will leave as is until it over heats this comming summer. BTW I was running a cooler T stat (around a 180) when all this happened. put in a stock T stat and still had a few issues with cold weather.

 

Yes an engine can run too cool, IF the thermostat sticks open & permits an excessive amount of coolant to pass to the radiator for cooling, or you've used the wrong heat range thermostat, or the new one is bad.

I know you said you've replaced the thermostat, but if in the past you've used the wrong recipe coolant, it can cause cavitation that'll eat at the water pump impellers, or if the coolant was ignored to the point that it got so acetic that the water pump impelleres disintegrated, those pieces are likely still in the system somewhere & it would't take a very large piece to lodge in the thermostats seat & prevent it from closing as it should & that cooant by-pass can cause over cooling.

If the coolant was in that bad a shape, sludge, pieces of the impellers, corrosion, hose liner, ect could have also clogged the heater core & radiator.

SO, have you disconnected the heater hoses at the firewall & "back flushed" the heater core separately????

If not, this might help flow through the heater core.
Be careful not to apply full home 60lb water pressure to the heater core, as it's only designed to withstand 15lbs or so & if it's in a weakened state from internal corrosion, it could pop from over pressure.

So maybe consider pullng the thermostat & checking it out for debris, or if you suspect it, just replace it again with an OEM one, or a like design, that has the built in "air bleed valve", as this will allow the system to burp air easier after a refill.

Also on the refill, if you'll do it with the front end facing up hill, the steeper the better, it'll help the air migrate to the radiator cap area & burp.

So after adding enough of the specified coolant to see it in the radiator, but not compltely full to the top, "milk" the lower radiator hose several times & the coolant level will rise, then drop to a lower level, if more air was expelled past the thermostat air bled valve.

Once the level remains steady when you stop milking the lower radiator hose, top off the radiator & overflow tank, replace the radiator cap (is it new too????) if not, with over 200K miles, replace that puppy also.

Then with the front end raised, the heater temp contol on max heat, start the engine & let it fully warm up, such that the thermostat opens fully & run the engine at a fast idle for a few minutes, then shut it off & let it fully cool down & see if the overflow tank level drops.

If it does, the system & radiator cap has worked as it should & burped some more air out & topped itself off with coolant from the overflow tank.

So add some more coolant to the cold fill line & repeat the run & cool down cycle until the over flow tank stops dropping.
Then watch it for a few days, in case it burps some more.

Maybe checking the thermostat seat for debris & back flushing the heater core will help.

Make sure you use the Ford specified recipe coolant, so it's compatable with the engine & coolant system parts.

A bunch more thoughts for pondering, let us know how it goes.