1993 4.0 overheating

[Bstandsforbama]

Hello, new to the thread. And very sorry if this has been posted before. I also am having trouble finding info on the web. Doesnt help that im bad with technology haha. I have a bone stock 1993 explorer sport. New water pump. New thermostat. New radiator. Changed the spark plugs and although old and shot I didn't see anything concerning. When I bought the vehicle it would run a little hot at a red light but when I was moving it would cool down to a normal temp. First thing I checked was the thermostat. It didn't have one. That made me assume it was circulating to fast and wasnt cooling it down when stopped. (Been an issue with other vehicles not that familiar with 4.0s though) after flushing the system. New thermostat. Etc. I fired her up and she ran nice and cool. Drove her around the block and she started running a little over the middle. Went to take the cap off to check to see if their was any air pockets and let her burp and she just spewed steam and water out until the radiator was basically empty. It did this when it didn't have a thermostat in it too. She does have a little misfire. Better after changing the plugs and wires along with oil change etc. I bought it with a new radiator and water pump already installed. Although it didn't have a thermostat the housing hadn't been off in a LONG time. Im piecing it together they obviously had an overheating problem. I've had other ford's all 5.0s that have done the same thing but didn't have a bad head gasket.. Is there something to look for common with the 4.0s? I bought it as a project truck tor put a 302 in but would like to drive it for the time being. But to go over again it's bone stock. New water pump. Radiator. 180 thermostat. Nothing fishy with the old spark plugs that were in it. Doesn't run HOT just a little over middle after a while and has crazy pressure built up (did this when it had no thermostat too). No leaks. No clogs. Flushed it and burped her. Oil looked good. Coolant looked fine. (Prior to tune up. And it sat for a while) any and all advice is greatly appreciated. I considered a new radiator cap but dadgum I can't imagine that would cause it to build up that bad. I'm not ruling out headgasket just saying I didn't really see any signs of it being bad. But then again it's not always easily diagnosed. Thanks.

 

[trashtruck]

have you checked the clutch on the fan? if you purchased it with the overheating problem it's possible one or both heads are warped.

 

[mekelly]

I 2nd TrashTruck. Warped heads, head gasket, fan clutch.

Rent (you get all your money back) a coolant pressure tester from Autozone. Connect it, start the engine and see if pressure starts building right away (before the thermostat opens). If so, you're getting combustion gases in the cooling system.

 

[Bstandsforbama]

I considered the fan clutch though it appeared fine. Most of the time when the fan clutch is bad it will slow down when the rpms go up but function normally when idling. She ran cool at an idle until I drove her. Even when I bought it and was looking at it I let her idle and she ran cool. It's like as soon as I start driving it she'll run a little hot and from there on out she won't cool back down. I could crank her up now and let her sit for an hour and she'll be fine. Go down the street and it's all over from there.... I'll check the fan clutch although looks new. Change the cap. Flush her again. And if I can't figure it out I suppose I'll start my 302 build a lot earlier than expected haha I guess I was hoping for a solution instead of having to yank the motor. But deep down I felt it was a head problem. Black on black 2 door 5 speed with no rust and I paid less than the motor and trans is worth as they sit so I'm not terribly upset. Was gonna get a v8 swap one way or another. Thanks for the help guys and if anyone else wants to chime in feel free. There's always hope
MeKelly I know it's not accurate to go by visuals but she wasnt being fishy at all before the stat opened up. She drank from the radiator and I conintued to top her until she was steady. Although I messed up and didn't back fill her first but she did eventually cycle through. I would say it could have air in the system because of that but because she did the same thing without a thermostat imma rule it out. Although did run cooler when driving without the stat it still got up there when beat on a little bit.

 

[Rhett]

In addition to the good advice above...I would re-burp (sounds bad heh) since you drove the truck and then burped it. You already know that's not an effective way to burp it, not to mention dangerous for you and the engine.

This time to do it is when the engine is cool, like first thing in the morning. I like to squeeze the upper hose while the stat is opening on this truck, while monitoring the level in the open radiator. It might take 2 burp sessions (over a 2 day period, for example) to purge all the air. Never do it when the engine is hot.

 

[Bstandsforbama]

Well since I already goofed up by not back filling her I was hoping to check it and put more water in if needed. She wasnt deathly hot and I would never just reach over and yank the radiator cap off. She could be barely starting to warm up and it would spew out like this. Again just concerned since everything is new and she did the same with no thermostat too.

 

[mekelly]

Jack up the front of the truck to ensure the radiator cap is the highest point of the cooling system.

Take the cap off, start the engine and turn the heater on. Once the thermostat opens and starts circulating the coolant, it's pretty easy to ensure all the air is purged.

 

[Bstandsforbama]

I went down to my shop last night and topped the radiator off.. the overflow was empy and the hose had popped off.. it was gucky so i cleaned it. filled it. and put the hose back on. didnt tamper with anything and cranked her up. she ran very cool. for a while.. and then slowly started running hotter and hotter. once it hit a little over half i shut her off let her cool. checked the hoses and they were hard as a rock. and the cap was dang near melting lol. once I released the cap some she spewed all over the place. checked the cap and it looked fine. it was a 13 psi cap. I believe the original was a 16 right? not sure and I dont think its a big deal but i stole the 16 psi off my foxbody. filled her back up. put the cap on and fired her up. she ran VERY cool.. then slowly started going up. all over again let the pressure out and did it one more time. this time the temp went DOWN. and went down low. decided to leave my basically brakeless 41 chevy that was a death trap at the shop and drove the xploder home which is 4 miles away. i babied her and cruised and she ran right under the N and went right on the N when stopped at a redlight. but went back down a tad when moving again. now I'm no master mechaninc but I don't think a blown head gasket (or any type of head issue) will fix itself nor would the temp go down when driving. Could be wrong. Usually am lol. she stayed cool and I made it home. Gonna check it again in the morning. Just frustrating because I bought the car with everything new except having a thermostat in it. I don't know the history of the car or whats been done or whats been happening. But I'm slowly piecing it together and clearly the previous owner had a problem with it as well. I know putting a 16psi cap on it didnt solve all my problems but it definitely did the trick to get me home. My buddy has a shop near mine I'm gonna run it by him and let him inspect it and test it. get a second hand opinion on it. as well as use yalls advice. Thank you all for the help so far. By the way.. could anyone point me in the right direction to a thread or site about doing the 5.0 conversion.. I know a little bit about it and have read some threads but I have questions about clearlance and fab work. I believe some stuff has to be relocated and I had questions about the headers. etc. Never done a swap in something with such a small engine compartment. Would like to be prepared. Gotta give props to guys who put ls1s in Honda Civics ya know haha! But again thanks.

 

[trashtruck]

curious how neither a 13 or 16 lb cap won't release pressure. it would be interesting to know how much pressure is building.

 

[Rhett]

Doesn't sound good with that much pressure building up.

For the 5.0 swap, there's a lot of info over at TRS (The Ranger Station) too. Also check out James Duff's website, they have more info on it. The transmission tunnel will probably require modification. Usually the heater box too. A lot of guys have to cut the radiator support for front clearance. A 1" body lift will help for the oil pan clearance.
Seems like JBA made some headers that fit (JBA Shorty headers?? maybe not made anymore) but it's been a long time...

 

[Centaurious]

In my experience a 13# cap is too low for a 4.0 OHV engine. They will cool more effectively with a 16# cap as it reduces the chances of overheating from the heads.

 

[Bstandsforbama]

well... as if things couldnt get more confusing and aggravating its the opposite completely now... doesnt run even slightly hot when driving... only when stopped. I've tested it a bunch.. SOOOO.. the only logical thing now I guess thats quick and easy is to change the fan and fan clutch.. (fan is old and cracked, clutch looks brand new) Don't understand how it went from running cool when parked and over heating when driving to the opposite OUT OF NOWHERE.
And thanks for info on the swap. I was gonna get a 5.0 explorer with the GT40s and start building it. goal is about 500HP. I'll worry about tranny when the time comes. rear end. etc. But see here is my biggest concern about clearance. is it possible if I lower it?? Alot... lol Not like a bagger but hugging the road.

 

[Explorin'VA]

I would try out a new fan clutch first, that fixed my overheating problems on my 94. Especially if overheats at a stop but cools when you start moving.

 

[larrydd999]

If your fan is old and cracked, by all means replace it. You don't want it suddenly coming apart. I do suggest you purchase it locally - I mail-ordered one and it arrived with cracks. Not as bad as the one I replaced, but had I purchased it locally I would have taken it back. BTW, there are multiple choices in fan clutches, depending on your cooling needs.

 

[Suicide77]

Another thing to keep in mind considering the vehicle is 23 years old, the temp gauge on the dash could be going bad. Mine did all sorts of back and forth shifty stuff when it finally went before finally settling on the left of the 'N' as normal.

 

[Bstandsforbama]

Definitely changing the fan either way haha I don't drive it often. Just a couple times to my shop. I just wanted to figure out the overheating issue before buying anymore parts. Everything seems to be alright now engine wise aside from running hot unless moving. When I first inspected the fan clutch it appeared brand new. And i didn't notice anything wrong with it. Today I grabbed a rag and applied some force to the fan blade and was actually able to stop it. Gonna go ahead and assume it's bad..But wasn't my issue originally. I must have solved the overheating problem and THEN the clutch went out. Perfect timing huh? I also replaced a headlight bulb and directly after the other bulb blew. I mean literally right after...Seems to be a pattern going on haha. I'm replacing the fan and fan clutch in the morning and see what happens.

 

[Bstandsforbama]

I don't wanna say the gauge is dead accurate but it seems to be fairly accurate. Have considered looking into replacing some stuff after the clutch and fan.

 

[Sip]

I went down to my shop last night and topped the radiator off.. the overflow was empy and the hose had popped off.. it was gucky so i cleaned it. filled it. and put the hose back on. didnt tamper with anything and cranked her up. she ran very cool. for a while.. and then slowly started running hotter and hotter. once it hit a little over half i shut her off let her cool. checked the hoses and they were hard as a rock. and the cap was dang near melting lol. once I released the cap some she spewed all over the place. checked the cap and it looked fine. it was a 13 psi cap. I believe the original was a 16 right? not sure and I dont think its a big deal but i stole the 16 psi off my foxbody. filled her back up. put the cap on and fired her up. she ran VERY cool.. then slowly started going up. all over again let the pressure out and did it one more time. this time the temp went DOWN. and went down low. decided to leave my basically brakeless 41 chevy that was a death trap at the shop and drove the xploder home which is 4 miles away. i babied her and cruised and she ran right under the N and went right on the N when stopped at a redlight. but went back down a tad when moving again. now I'm no master mechaninc but I don't think a blown head gasket (or any type of head issue) will fix itself nor would the temp go down when driving. Could be wrong. Usually am lol. she stayed cool and I made it home. Gonna check it again in the morning. Just frustrating because I bought the car with everything new except having a thermostat in it. I don't know the history of the car or whats been done or whats been happening. But I'm slowly piecing it together and clearly the previous owner had a problem with it as well. I know putting a 16psi cap on it didnt solve all my problems but it definitely did the trick to get me home. My buddy has a shop near mine I'm gonna run it by him and let him inspect it and test it. get a second hand opinion on it. as well as use yalls advice. Thank you all for the help so far. By the way.. could anyone point me in the right direction to a thread or site about doing the 5.0 conversion.. I know a little bit about it and have read some threads but I have questions about clearlance and fab work. I believe some stuff has to be relocated and I had questions about the headers. etc. Never done a swap in something with such a small engine compartment. Would like to be prepared. Gotta give props to guys who put ls1s in Honda Civics ya know haha! But again thanks.

 

[Sip]

I’m having your same exact problem with my Ford Explorer 91. Did you ever figure out the problem?

 

[sd_iconoclast]

The symptoms you describe sound very similar to what I experienced when my heads cracked.
This is VERY common in 4.0s. They crack between the valves. This has happened to me three times in my '91 EB.
I bought it with 137K on it and one head was cracked. The previous owner thought it had a blown head gasket. I replaced that head and almost immediately, the other head cracked. Then, just recently, I cracked one of the new heads, although this one was my fault. I had a vacuum line pop off the octopus and I drove it that way until the #6 spark plug melted.
The good news is that replacement heads are cheap. I have paid about $125 each for new bare heads. Dont reuse factory heads. Buy the chinese replacements as they are thicker.
With each incident, I drove the car for about 10k with the cracked head and I probably could have driven it indefinitely.
The temp would start fine, then it would take off to between 200 and 220 (I have a 180 degree thermostat) and then come back down again.
I would see a slight buildup of milky sludge on the oil cap and later I saw the same inside the valve covers. My oil looked fine otherwise.
I was getting alot of buildup of brown stuff in the radiator.