Engine running hot and no heat inside - Thermostat?

[Forder]

This past week, my ol'94 has been running hot (almost past the "L" on "NORMAL" on the gauge) when sitting idle and there's no heat coming out of the vents. But when I start driving highway speeds, the temp gauge goes back down to the middle in the normal operating area and the in-cab heat comes on and boy is it HOT! Almost burns your hand if you hold it to the vent for too long.

So I'm guessing that the thermostat is stuck closed or something? I thought if anything they would fail-open causing the engine to run cool, but I'm no expert which is why I'm asking you all . I don't know how the thermostat would affect the HVAC either though. My dad says they may be separate issues (heater core and thermostat).

Thanks in advance for any help! I hope to fix everything this weekend. I need to replace the fuel filter and flush the coolant anyways since I haven't done that in the past decade I've owned this thing, lol. Any good write-ups on the fuel filter? I see one for a '96 on here, but not for first-gens.

 

[mr cribb]

This past week, my ol'94 has been running hot (almost past the "L" on "NORMAL" on the gauge) when sitting idle and there's no heat coming out of the vents. But when I start driving highway speeds, the temp gauge goes back down to the middle in the normal operating area and the in-cab heat comes on and boy is it HOT! Almost burns your hand if you hold it to the vent for too long.

So I'm guessing that the thermostat is stuck closed or something? I thought if anything they would fail-open causing the engine to run cool, but I'm no expert which is why I'm asking you all . I don't know how the thermostat would affect the HVAC either though. My dad says they may be separate issues (heater core and thermostat).

Thanks in advance for any help! I hope to fix everything this weekend. I need to replace the fuel filter and flush the coolant anyways since I haven't done that in the past decade I've owned this thing, lol. Any good write-ups on the fuel filter? I see one for a '96 on here, but not for first-gens.

I say thermostat... sounds exactly like what happened to me in October. I did a write up for changing the t-stat:
http://www.explorerforum.com/forums/showthread.php?t=334499

 

[Anime]

My experience is the thermostats on these, including the OE Motorcraft ones, fail slowly, letting the engine temp creep up a few times, then eventually getting stuck closed.

Replace the thermostat ASAP, even if it means just draining some of the coolant and buying a $5 Stant stat.

I would suggest replacing the antifreeze/coolant with Zerex G-05, it's the gold/yellow stuff available at NAPA. The green Prestone and other coolants at wallyworld and other parts stores seem to be harmful to the gaskets of systems designed for earlier coolant like the Explorer. I've had great results with the G-05, it's the same stuff Ford uses in their newer vehicles. Zerex also makes 'original Green" which is the correct green coolant if you want to use that, it's slightly cheaper than G-05.

Might be a good time to replace all the hoses too if it's been a decade, both the top/bottom radiator hoses and the heater hoses, just get a bunch of 5/8" heater hose for that.

Be sure to follow the proper procedure for burping the air out of the cooling system when you refill it, and you should be set for awhile.

 

[Currency]

I just buy prestone 50/50 from walmart. Love when it's on sale for $10 a gallon and stock up because they generally charge $13.50 in my area. I do have a really minor leak at the top of my radiator. So I generally keep it 3/4 full.

Mine never has hit the 'normal' on the gauge unless I'm playing really hard in the mud or something. Then I have seen it hit 'normal' but afterwards it drops back down to right above the line past the C.

 

[Forder]

I say thermostat... sounds exactly like what happened to me in October. I did a write up for changing the t-stat:
http://www.explorerforum.com/forums/showthread.php?t=334499

Thanks for the link. I'm about to run out to the parts store now to do this. Me and the wife have been really sick all weekend and I'm just now over it (she's getting over it now). Fortunately I have Presidents day off today so I have time to do this before the work week.

My experience is the thermostats on these, including the OE Motorcraft ones, fail slowly, letting the engine temp creep up a few times, then eventually getting stuck closed.

Replace the thermostat ASAP, even if it means just draining some of the coolant and buying a $5 Stant stat.

I would suggest replacing the antifreeze/coolant with Zerex G-05, it's the gold/yellow stuff available at NAPA. The green Prestone and other coolants at wallyworld and other parts stores seem to be harmful to the gaskets of systems designed for earlier coolant like the Explorer. I've had great results with the G-05, it's the same stuff Ford uses in their newer vehicles. Zerex also makes 'original Green" which is the correct green coolant if you want to use that, it's slightly cheaper than G-05.

Might be a good time to replace all the hoses too if it's been a decade, both the top/bottom radiator hoses and the heater hoses, just get a bunch of 5/8" heater hose for that.

Be sure to follow the proper procedure for burping the air out of the cooling system when you refill it, and you should be set for awhile.

Thanks for the suggestion. I wanted to do a full coolant flush while I'm at it anyways since it's way overdue, I'm sure. I'm not sure what the proper procedure is for burping the air out of the system. Is there a write-up around for flushing out 1st gens on here? (Edit: Found this excellent sticky )

Thanks for all the help everyone!

 

[Youngcheezy]

i had this problem with a car i had a while back. First thing i thought, oh great my thermostat is done ... then i popped the hood and realized i didn't put my radiator cap back on.
like you, i was running hot and had no heat inside the vehicle.
maybe there is a leak..? or bad circulation..?

 

[Youngcheezy]

sorry for the quick hijack, but what do you guys think about that radiator sealant crap? it looks like a million little aluminum shards in a small tube.. I used it once in a car i had and after i used it i think my coolant problem got worse! oh well, car long gone and smashed up at the junk yard now though.. but quick opinions please! don't wanna make the same bad-decision twice

 

[FLwireman]

Stay away from the sealant crap. I used that stuff and in the long run I had to have my tranny rebuilt due to overheating. I ended up changing the T-stat, water pump and radiator. That $4.00 bottle of sealant cost me big bucks in the long run.

 

[Forder]

Well it was an easy fix. I thought the coolant level was good by looking at the cold fill level on the reservoir, but the reservoir is almost opaque now and I misread it. It was bone dry. Opened up the radiator cap and the coolant level was at least 6" deep. It was about a gallon low, lol. I topped it off and all is good now. Heat works great and temps are normal.

At least it was an easy fix .

Thanks all!

 

[nexis]

now the question becomes where did the gallon of coolant go?

 

[Forder]

now the question becomes where did the gallon of coolant go?

Well I said in the OP that I haven't flushed my coolant system in a decade; what I should have said is that I haven't touched my coolant system in a decade, lol. So over the course of 10 years or so, I'm sure it evaporated/broke down or something. If there is a leak, then if it's that small, then I'm not that worried about it :. I definitely haven't noticed any drops below it in the driveway though.

 

[jd4242]

ps thermostats have nothing to do with heater cores,water runs through the core all the time no matter if the tstat is open or closed

 

[Tony H]

Sounds like you are low on coolant.
Engine gets hot and there isn't enough to flow through the heater core

 

[jd4242]

Sounds like you are low on coolant.
Engine gets hot and there isn't enough to flow through the heater core

Well it was an easy fix. I thought the coolant level was good by looking at the cold fill level on the reservoir, but the reservoir is almost opaque now and I misread it. It was bone dry. Opened up the radiator cap and the coolant level was at least 6" deep. It was about a gallon low, lol. I topped it off and all is good now. Heat works great and temps are normal.

At least it was an easy fix .

Thanks all!

Did you read the whole thread?

 

[bftank]

check your heater valve just before your thermostat. mine had a small crack that weeped out a gallon of coolant overtime. i didn't see any leak or any discoloration around it. just heard it hissing after shutting it down this winter.

just for maintenence purposes anyways