Hey guys, I posted a few weeks ago with an overheating problem, thanks to you that's fixed, now the problem is quite the reverse. Now I'm having trouble getting the temp into the normal zone on the gauge (gauge sensor has been replaced, not issue with that). And what baffles me is sometimes it will go to normal zone right about where the letters N or O is "Normal" are and stay there, and my vents will stay nice and warm the enitre time im out and about.

But more times than not, it will stay below normal, my vents will fluxuate like if I slow down or stop they'll get cold, or accerelate it'll warm up. I'll mention also it seems a little warm when I first start truck, then drop to cold.

I replaced the thermostat before, is it possible this is bad? out of the box? I had just put it in when I had the overheating problem. Any other thoughts?

The fluids levels are ok, and this baffles me, at least it's drivable, as it really wasn't with the overheating problem. Thanks for any input!!!

 

It is possible your thermostat is bad. Anything mass-produced can be these days.
If you want a cheap test, try pulling it out, putting it in some water with a thermometer and warming the water on the stove. If the thermostat opens earlier than the rated temp it is bad, if it opens at the right time or really close to it (+- 5*) you are ok. Might want to try several times to make sure it is consistant. At least you will know for sure weather it is your problem or not without spending more money.

 

Ok heres an update:

driving home from my job third shift (less than 25 degrees out) on a 55 mph road my heat will flucuate. BUT when I got to a 35 mph zone near home it got real nice and warm, and the temp gauge evened out and stayed normal (near o).

So I tested this theory, I drive around the block 3 times. The first two times I locked cruise in at 35 mph, both laps around it stayed HOT and the gauge was in normal. However, on the third lap around, going 55 mph, same issues as before, colder temp (below normal mark usual, and flucuating or no heat)

Now also when I got home I opened up the pressure release (the radiator cap has a release valve to blow pressure through resevior). After the 55 mph lap the overflow bottle was near full (not sure if it was during 35 mph test too) AND when the pressure was released there was more freaking air... Its gotta be coming in somewhere too...

Any ideas!!! I'm so lost! Still!

 

I hate to say it, but maybe you have a bad head gasket, or cracked head. I would have the system pressure checked and see if it holds pressure. A blown gasket will probably hold some pressure, but a cracked head will not hold much at all.
Other than those two items I can't think of anything else that would add air to your system.

 

It could just be a bad rad cap or the wrong pressure.

 

Would a bad radiator cap pull in air?

Because I seem to get air in everytime I drive.

If it is a head gasket it's not that big of a deal, the engine is rebuild a few weeks ago and is under warrenty, labor too. And if it was a head gasket, wouldn;t I be losing fluids?

 

Unless you have been through this you'll Never understand it.....



IT'S the Heater Core... It's clogged
u can replace or clean it out... there cheap

 

So if a heater core is bad or clogged it can suck in air too? And if so is there anyway I could test this (what would driving with the heater off do)?

I just having trouble trying to think how the heater core is going to make temp gauge go up and down and flucuate heat, and somehow theres air in the system. But does anyone else think that sounds logical, I mean, I have no idea (obviosly)?

 

The problem isnt that it's sucking air. The coolant system (if the radiator cap valve is closed) is a closed system.

It sounds to me like the system is vapor locked. These trucks were designed bad, unless you have a 3 inch body lift. The upper radiator hose is higher than the radiator filler neck. Thus, there is always going to be a pocket of air in that upper radiator hose, unless you somehow get it below the level of the filler neck. Thats just how gravity works.

What is happening is, little by little, the coolant is slowly working its way through that upper hose, and once the fluid gets into that upper hose, you will open your cap and see that it is "low." What you need to do is let the truck cool off, pull the cap, start it up, and let it run into it get hot, or until you see the coolant moving in the radiator (indicating that the thermostat has opened.) Then once this happens, add some fluid, and keep squeezing the upper hose to get the air out and let coolant in.

Another way to get the air out of that upper hose is to actually bend the hose down around to inside the fan shroud, which is lower than the filler neck of course. You do not want the engine running, by the way. Then fill it up and work that upper hose until you can tell its full.

That would explain the movement of the gauge. As far as the heater, the times that it goes "cold" could be one of those times where the pocket of air works its way into the heater core, or the heater core could have air in it, itself. A clogged core will also cause it to fluxuate, but not with engine temperature, as you indicated it's doing.

 

to make sure you do not have blown head gasket ,open the radiator cap while the truck is running if you see bubbles in the radiator you have a blown head gasket ,like the other guy said sometimes you really can have a bad thermostat from the get go,go buy a motorcraft one and install that one,they may have given you one for the wrong temp,because the computer has on a 94 the temp control sensor for the computer and one for the guage,if you replaced one of those you may want to check the other one?

 

If you had a blown head gasket, you'd know it. He would lose a lot of fluid. Are you losing fluid by the way depotops?

 

Ok I'll try to explane...


But like I said unless you have been through it it's hard to understand..

the heter core being clogged will SOMETIMES allow water to pass through and sometimes NOT..

Like when there is NO pressure on it..

when water is NOT passing through. there is NO heat and the temp Guage will GO up like mad....

when TS opens it will pass a little water NOT what it's suppose to ( I have never seen one totaly clogged)

at this point you may get a little hot air....

and the temp guage will decrease ( like mad)

simple test....

pull the outlet heater line off and start truck....If your full of coolant catch it....

you will soon find that it will flo a little BUT IT SHOULD FLO LIKE A WATER HOSE...

simple test that takes about 5 minutes....

I've seen this a million times.

 

Air in rad hoses....

never herd of this one..... water is heaver than air.... hence the water pump it forces water to circulate..... that's Y you have a overflo... to catch it and suck it back in when needed....

 

I've heard of it, and see it multiple times. If the UPPER radiator hose is higher than the filler neck of the radiator, theres an air pocket. You can fill the radiator up to the point where it's overflowing out of the neck, but how is the air going to get into that hose if it is above the filler neck? It's called gravity my friend, and 6th grade science.

 

sorry I fail to see what a little of a lot of air in any cooling system has to do with the price of tea in China...

most auto's on the road have air in the cooling system

mine ran 2 years with just 1 gallon of coolant in system and nothing else

belive it or NOT MOST cat9 's will explode the rad if all air or almost all air is removed,,,

Not sure how you would remove all the air is a cooling system OR why ?