Engine not heating up

[Pnwrager]

Hey all. I'm fairly new to working on vehicles and recently finished up a replacement on my cooling system. Replaced the radiator, hoses, water pump, thermostat and housing. Now my temp gage will go up about 1/4 of the way then drop back down so I know that the thermostat is opening and closing. And my mpg' s went from 15-16 down to 13 on my last fill up. So I don't think it's simply a sensor reading the temp wrong. I'm lost on what to do next except for taki ng off the thermostat housing and making sure the thermostat isn't in backwards. If anyone has an idea on what I should do your input would be greatly appreciated. Truck is a 91 4.0l v6 if it makes any difference.

 

[Vincenthdfan]

Did you put the spring side of thermostat toward the intake manifold...basically facing aft?

That is the correct direction.

You also want to make certain you got all of the air out of the system.

Have the front end of truck angled uphill, doesn't take a lot....then with radiator cap off, let engine idle and warm till thermostat opens up....you'll see numerous bubbles coming up out of radiator neck as you do this.

I just got done doing a new heater core, thermostat, and water pump in my 93 4.0 so its all very fresh in my memory.

 

[Pnwrager]

I'm 99% sure I installed it in the right direction. When I burped the system it was sitting flat so maybe I'll try it with the front end up

 

[RonD]

Thermostat for Rangers is rated as 190-195degF, not 160 or 180degF

Simplest way to refill without trapping air is to remove 1 heater hose at the firewall, the one from upper intake is best but either will do
Fill until coolant/water starts to come out hose and/or Heater Core
Put hose back on
All air is now out, or enough so any remaining will end up at the top of the radiator after thermostat opens the next time.

Center of Ford Temp gauge is about 200degF, so after warm up needle should be just below 1/2, above 1/3 for sure

Make sure thermostat is working without leaking:
Start cold engine and feel upper rad hose will be stone cold of course
Turn heat control in cab to HOT, fan can stay off
Wait 3 minutes or so and feel heater hose, should be warming up
Feel upper rad hose........should still be COLD, if it is warming up like the heater hose then thermostat is leaking
Upper rad hose should stay cool until engine temp gets to 190degF, then it will start to open and hose and rad will start to warm up



Not that it matters now but most thermostats come with a "jiggle valve", yes that is its official name, lol
It a small hole in the thermostat plate with a loose metal pin in it
This hole should be mounted at 12:00 position, highest spot, it is there to let Air out as you refill the engine cooling system or to let any trapped air out after engine heats up and cools down a few times.
It is called a jiggle valve because coolant flow causes pin to "jiggle" in the hole keeping it open all the time.

Next FYI, Reverse the heater hoses at the Firewall every few years, this keeps the core cleaner by back flushing any debris out the way it came in

 

[Pnwrager]

Thermostat for Rangers is rated as 190-195degF...

Is it possible that the knuckle heads at O'Reilly sold me a thermostat that opens up at a cooler temp?

 

[RonD]

Look at the box, or look up the part number

If you said 1991 Ranger then you would get a 192degF thermostat

But "the box" can have wrong thermostat inside, doesn't happen often but does happen.

And any "new" part means its NEVER EVER been tested, that's all "new" means now
Used to mean "it works" not any more, just means no one but YOU has ever touched it so "good luck, and we will replace it if its bad"

 

[Effieman]

My temp gauge hasn't gone up nearly as far since I replaced my radiator last year. BUT, being a Ford, the heater still kicks butt......So, I finally connected my scan tool and got a temp reading of 186, so I'm not going to worry about it.

 

[Vincenthdfan]

I gotta tell ya...I've been working the bugs out of my little '93 4.0 4x4 XLT since I got it last March.

I don't know why I'm so driven to work all the bugs out, I guess the lil truck has kinda grown on me, lol.

Anyway, my latest was a new thermostat, water pump, and heater core...

The temp gauge on the Ford is the oddest thing I've ever seen in any of my vehicles....fluctuates from 1/4 to 1/2, back to 1/4, repeat...

I seem to remember a post you made way back when RonD that this is normal operation for Rangers, with the excess pressure routing from water pump to heater core repetitively, thus the temp crawl up and down.

Even though its normal, it sure looks odd??

 

[RB7 Ranger]

low on coolant/ air pocket,
wrong thermostat
air being introduced into closed cooling system