Ok I recently purchased a 1993 Ford Ranger. 4.0 5speed 4x4

I have been having an issue with the temp gauge going from cold to hot staying there for a few seconds and then going back down to cold.

first things first.
The truck has a new temp sending unit as of today
the cooling system has been flushed and refilled and I believe all the air is out of it because the radiator is full even though I have parking up hill and doing everything people have said to in order to "burp" the system
I did run an exhaust gas test and it came back negative no gas in the cooling system, and we ran the test 4 different times.

Other then that the engine runs fine, the heater is one of the best i have ever had in a vehicle it blow warm but once the engine runs for a while it blow hot but not too hot and stays constant in air temp.

So my question is why would the temp gauge be acting so weird?

I now ask the floor for help

Thanks

Eddie

 

i have a manual temp guage in my 94 3.0 and let me tell you they fluxuate alot... it is possible i did not "blurp" my sysmtem correctly

 

Replace the thermostat.

I have a second gauge as well, its located in the upper hose. Neither gauge moves a much once the truck is up to temp.

 

With the engine warmed up to temp and idling , carefully inspect the lower radiator hose to see if it is collapsing.
With the engine off and cold , squeeze the lower hose feeling for soft spots , it may be collapsing inside where you can't see it.

 

ok so update, I replaced the thermostat and the gauge move still but it is not so dramatic it only goes from the "o" in Normal back to the "m" or the "a" and back down to the "o". and the lower radiator hose is not collapsing nor does it have any soft spots. BUT the upper radiator hose does make a weird "thumping" noise after i have driven the truck for a while.


That is all for now, I thank you all in advance for your help and wisdom.

 

My gauge usually does not fluxuate too to much how ever it will jum 20 degrees at times while driving my second gauge is on the upper hose in the spot where the thermo sensor should be

 

I know that they are not supposed to move that why Ive posted here, I have no idea how to stop the gauge from moving like it does. All i know is it is not normal

 

The upper hose thumps, because there is air in the system.

 

Thank you, now on to my next question how do I get the air out. I have parked it up hill and let it cool checked the fluid and repeated. im at a loss on this one, all of my other cars have always had a bleeder valve for air.

 

Let it idle with the cap off heat on full hot.

The bubble will work into the radiator and out. My take 10 to 20 minutes depending on weather.

 

Park it somewhere level and let it idle with the radiator cap off until air bubbles come up...

 

when I do that the truck spits out the fluid

 

Thats the air bubble moving around. You may need a new cap too.

Make sure the truck is cold before opening the cap, as it will puke coolant if its not.

 

Ok thanks, I have done that and I have a new cap already, it got a little better, but I do not know if i need to let it bubble out for longer then the 20 minutes that I did, will the coolant stop puking out when all the air is out?

 

When cold it should only dribble a little bit, as the tstat cycles the air bubble should be forced into the radiator. It should not be more than a splash.

I am beginning to wonder if you have another issue. Do you lose coolant and cant find a leak?

 

It does only bubble out a little bit every could of minutes, nothing major, i have already checked for leaks and there are none that I can see, and I do not lose coolant whenever I check the coolant levels they are always right on. lol

 

Once you do it once you should not need to do it again, unless there is an unresolved issue. Verify your res tank and hose are clean and flowing.

Not sure why the upper is making noise, unless maybe the tsat is in backwards.

 

thanks for the response the hose and res tank are clear and working, the res tank has fluid in it, I just dont think I let the system air out long enough maybe, i dont know though its not overheating so im getting to the point where I am not worrying about it as much. now I have to move on to a Throwout bearing and clutch kit lol it is making some serious noise now.

 

I just ran into this same issue with my 94 4.0 last night. I'll post back with what I come up with. I'm thinking air pockets with out a doubt. I also picked up a new t-stat as well. I can here the air pockets passing threw the heater core when driving the truck. I just put headgaskets and decked the heads about 1,000 miles ago so I highly doubt that is the issue but im going to block test it later today just to double check.

 

OK guys new development!

The upper radiator hose sprung a leak today and when I replaced it with a new one, I was letting the truck idle while filling it and letting the air bubbles come out and I noticed that when the you step on the accelerator both of the hoses collapse. what in the world is going on here?!

thank you in advance for your answers.

Eddie

 

I know it may be a pain to do but take off your water pump and see if the impeller is still there. On one of the threads here, someone posted a photo of his water pump and the impeller was all but missing. It could be yours may be on its way out.

 

Glad to see I'm not the only one with this issue. I have read many posts about the TSBs, with bypass kits and waterpumps. My situation is almost exact to yours crzyeddie. My son was given a 1990 ranger 4.0 by a grandparent. On the way ome with it we noticed the temp gauge fluctuating. We brought it home and replaced all the hoses, thermostat and cap. It then started to blow coolant out the cap collapse both hoses and thump in the upper hose. I used a motorcraft stat, Stant cap and gates hoses. Oh yea we also repalced the 22 yr old radiator thinking it was restricted. The engine and heater core look good and clean. I want to stay with this until we figure it out because too many seem to have the issue and I have yet to see anyone say they found the problem. Most give up and try to live with it. The only thing I haven't trid it the pump but it ha been replaced in the past. I may be to about the same point you are. Did you pull your pump yet?

 

Diesel1 I am glad and sad at the same time that so many people have had the same issue, at this moment and time I have replaced 3 thermostats, 1 temperature sending uni, 1 upper and lower radiator hose, 1 radiator cap and have flushed the system at least 5 times. To answer your question No i have not replaced the water pump because this vehicle is my daily driver and I have not had time to tear that much into the truck. But i will be getting a chance to at least check the water pump and see sometime this week so I will post here what my findings are. Thanks again for your reply and I hope together we can all get to the bottom of this issue.

 

Today I was successful. I got thinking about the coolant flow and what the added bypass kit that Ford had once offered did. The coolant bypass when the thermostat is closed is limited to the heater core circuit. If the heater core becomes restricted it limites the flow. The heater core feed comes off right by the temp sending unit and the thermostat and the return goes right to the pump inlet. If there is a pressure delta it will create and air pocket by the thermostat and temp sending unit. This caused the dancing gauge because the thermostat can not react in steam.

I replaced the heater core today even though I had good heat. It took care of the problem. No more dancing gauge, no more collapsed hose or coolant blowing out of the cap due to air pockets.

The hardest part of replacing the heater core was draining the coolant. Remove the vanity panel under the gove box. 4 screws to remove on the 1990 and there is the heater core. 20 minutes job and the part was half the price of the pump.

Hope this helps and possibly works for you as well.

 

Thank you Every one for your help in this situation Today 02/25/2012 I had to replace my water pump because it was leaking pretty bad. So along with the water pump I went ahead and put a brand new lower radiator hose and flushed the system once again, It appears that the problem has been fixed with a new water pump. I really appreciate the help I have received here and I look forward to learning more from all of you out there.

Eddie