hey guys hows it going? ever since i bought my truck (95 f350) its heat temp has been on n out of the normal on the gauge. recently the heat only starts getting warm when im accelerating or going an even speed but when i take my foot off the pedal it gets extremely cold. also, now the heat gauge will fluctuate greatly. it will go all the way from the normal up to the red and then back a few minutes later. any ideas? and the temp of the engine seems to have no effect on the temp of the heat. thanks guys

 

please clear up your communication.
When I read heat temp, I think temperature of air blown through the vents in the cab by the heater. Also, you have a temperature gauge in your truck which measures the tempurature of the coolant in your engine, not a heat gauge or heat temp gauge. Clear use of terms will help determine what your problem is.

also answer these questions:
when was the last coolant flush/fill?
when was the last system pressure test?
Are you losing any coolant?

 

hey sorry about that. the heat temp is the air being blown out of the vents, it only gets warm when i accelerate. and the temperature gauge is also what i mean by heat gauge. it fluctuates often.
i just topped the coolant off today, it was a little low
i havnt had a pressure test on the truck since i owned it (bought it last summer)
i lose coolant over the course of a few months. (i havnt checked it since jan and it was way below cold lvl

 

ok, better.
If you are losing coolant, you have a leak. A sealed system is very important because the system can't build pressure without it. Pressure is needed to properly circulate coolant, and also raises the boiling temp of the coolant. With a leak, liquid will drip out, or the coolant will evaporate and come out as steam. Find and fix your coolant leak. A radiator shop should be able to find it quick and easy. Have it flushed out while you are there.
2nd, your heater problem is being caused by a vacuum leak. Find it and fix it. Check the white vacuum hose that goes to the firewall with carb cleaner.
When you fix that and your coolant system problem, proper heating should return and your temp gauge should be happy.

 

ok thanks alot man. so your ruling out any thermostat or other problems like that

 

actually, come to think of it i do hear a hissing noise slightly inthe engine compartment. could that possibly be the vacuum hose broken

 

sry to not all throw this in one post but i had to get vacuum lines for the mustang i used to own and at most autozones and such type places, they only had "generic" tubes. do i need to go through ford.. i hope not

 

like puck said you should back flush your cooling system let it run for at least 30 min to get all you can out of the block and radiator if you use a prestone flush kit you can plug the outlet causing back pressure higher then normal is a good way to check for leaks and free up more of the crud in the system. turn off the engin let it flow until the water is clear dump a bottle of system cleaner in drive it a few weeks or 10 houres reback flush then 50\5o water coolant

 

If that donT help you can try replaceing the block temp senseor AKA temp sending unit which could be sending bad signals to the ECU (computer) causeing the overheating.

 

pressure check the cooling system, the ol ladies 94 f-250 w/a 351 used to do that, you could drive around and the guage (aftermarket) would continually run up to 205, then drop to 180, up to 205, back to 180....if it were just idling it'd stay @ 195 all day....it was a leaky head gasket (which i found after changong 2 thermostats, a water pump, and radiator hoping it was something cheap).

 

i would just pull the t stat and replace it. start there. then find your vacuum leak.

 

I disagree. Find and fix your leak first, then explore other options like the t-stat. BTW, if you do end up replacing the t-stat, only use a motorcraft OEM for your vehicle.

 

why only an OEM from motorcraft? I been runnin stants for years and never had an issure, a thermostat's a thermostat, just make sure you use the right temp.

Seriously tho, get a cooling system pressure tester, with the big fluctiation in temp, and coolant loss, theres an internal issue....even w/the thermostat sticking a little, you wouldnt lose all your heat, theres a bypass in the heating system that lets water from the block pump thru the heater core before the thermostat even opens to begin with.....I'm still bettin tis a head gasket

Makes more sense to check that out from the beginning than to try to "nickle fix it", only to end up spendin for thermostats, gaskets, waterpumps, ect. and STILL have to take it all apart in the end to do a head....trust me, been there-done that, and thats more frustrating than anything.

 

[QUOTE=Ford_for_Brains]pressure check the cooling system, the ol ladies 94 f-250 w/a 351 used to do that, you could drive around and the guage (aftermarket) would continually run up to 205, then drop to 180, up to 205, back to 180....if it were just idling it'd stay @ 195 all day....it was a leaky head gasket

I'm trying to understand why a leaking head gasket would cause the temp to fluctuate. Any ideas?

 

In all my years Have
I ever Heard of A Vechile w/ a blown head gasket run all day w/o overheating ok come on look nothing this man is saing leads to a head gasket like i said prevously back flush your system fix the vac leak and go from there that is the least evasive and most helpful thing you can do for your truck a vac leak alone can make it over heat, a sticky T-stat, he]] it can be a no. of things you have trubble shot it with us start simple you can spend all day and a weeks worth of money tring to fix the smallest of problems an ounce of prevention is worth a pound of cure!