Engine overheated, now running hot.

[iJimaniac]

Okay, so I've got a real head-scratcher.
Backstory; my 94 4.0 Ranger with either 150xxx (what the title says) or 250xxx (what I think it has) miles on it overheated on my way to work the other day. I was immediately concerned because I had vacuum seafoamed the engine two days prior. Upon inspection, I found and fixed a split heater hose that I thought might be the problem, but it was still running hot, so I limped home. It used to run consistently around 1/4 up the temp gauge, now it quickly goes up past half and fluctuates up and down rather quickly. I haven't pushed it up to highway speeds again because I'm thinking it would overheat again.

First step; I tested the thermostat in boiling water. It seemed to take awhile to open and not open fully, so I replaced it with a failsafe. No change.
Upon doing more diagnosis, I found the temp would sit around halfway up the temp gauge parked at idle, but immediately cool down to normal operating temp and stay there if I held the throttle at 2k rpm. Driving on the road is less consistent, but it generally heats up when I slow down. I took the top radiator hose off and got it up to operating temp. Nothing but a trickle. So I figured maybe the water pump impeller was corroded and not pushing water like it should. Took it off. Nope, just fine. Tested flow through radiator, it flows just fine. So that leaves what? Something wrong within the engine itself? Could a bad headgasket be causing this? No white smoke, and no foam in oil. Engine runs pretty much like it did before it overheated. I'm stumped on this, and really want this truck working by Monday. Any thoughts or suggestions on what to do next?


I'll add that I've inspected all spark plugs and wires and found nothing. No CEL.

 

[RonD]

Had a random temp issue on my '94 4.0l.
After warm up temp would rise and then fall but no related reasons

The heater core on this year is the water pump bypass, there is no heat control valve on either hose, coolant must flow thru the heater core all the time or temp will rise and fall.

You can back flush the core to try and clear it out or for $25 and 20 minutes, replace the core, 4 screws under glove box

 

[iJimaniac]

Had a random temp issue on my '94 4.0l.
After warm up temp would rise and then fall but no related reasons

The heater core on this year is the water pump bypass, there is no heat control valve on either hose, coolant must flow thru the heater core all the time or temp will rise and fall.

You can back flush the core to try and clear it out or for $25 and 20 minutes, replace the core, 4 screws under glove box

Hmm, maybe I'll look at the heater core more. I was assuming that wouldn't be the cause, but perhaps...

Side note; my oil dipstick is getting pretty dang hot after running the engine, but I can't recall if it did before this saga. Is that normal for rangers?

 

[RonD]

I replaced thermostat, and fan clutch, looked into lower water pump outlet to see impellers, flushed rad, flushed engine............. heater core never even entered my mind, lol.
Then read a post about some models using the heater core as the bypass instead of using bypass valve on the heater hoses.


Dipstick tube is bolted next to exhaust manifold, so yes it does get warmer than you might think.

 

[Angie]

Can't help any more than whats been said, however. i can relate what i have done in same circumstance. Ignore the factory electric gauge and buy a 20.00 aftermarket temp gauge. the sending unit could also be faulty and showing hot when it is at normal. had this happen on the truck I bought from a guy last year... said it over heats.... i couldn't find anything wrong so i bought a temp gauge, yes after a while it would show 220. after some digging i noticed no thermostat in the motor. put one in and end of probs.

that many miles the sending unit could be shot in the electronic one, if not at least you will know 100% the temp you are at.

one other thing, are you running straight water, 100% antifreeze or a solid water antifreeze mix/pre mix?

ps, my motors were 4.0l pre 94 style if that makes a difference.


have you checked and tested the clutch fan?

 

[iJimaniac]

Can't help any more than whats been said, however. i can relate what i have done in same circumstance. Ignore the factory electric gauge and buy a 20.00 aftermarket temp gauge. the sending unit could also be faulty and showing hot when it is at normal. had this happen on the truck I bought from a guy last year... said it over heats.... i couldn't find anything wrong so i bought a temp gauge, yes after a while it would show 220. after some digging i noticed no thermostat in the motor. put one in and end of probs.

that many miles the sending unit could be shot in the electronic one, if not at least you will know 100% the temp you are at.

one other thing, are you running straight water, 100% antifreeze or a solid water antifreeze mix/pre mix?

ps, my motors were 4.0l pre 94 style if that makes a difference.


have you checked and tested the clutch fan?

The mix is mostly water at this point because I had to replace a lot of lost coolant with what I had on hand.

I'm gonna rout around the heater core tomorrow and see what that does. It blows plenty hot so I don't think it's plugged, but you never know...

The clutch fan seems good (no wobble), but I'll maybe look at that more too.

 

[Andy D]

Getting hot at idle sounds like a bad fan clutch. They can be bad long before the bearing goes bad. Is the bottom radiator hose getting sucked closed? Is the cap holding ?

 

[Big Jim M]

Regardless of what the gauge says your engine isn't HOT unless it is puking it's coolant out the overflow. Make sure the coolant system is completely full and go for a ride, just to try to make it actually overheat.
So far all I have read here is the gauge is telling you it is slightly warmer than what USED to be normal. The engine will withstand more heat than the coolant will. So TRY to get it to puke! If it doesn't then your problem is in the gauge and not the engine.
Also like the previous poster said get a REAL temp gauge on there and you will see what the real temp is.
Big Jim

 

[oldyellr]

I had an overheating problem with my '85 Camaro for years. It would overheat in heavy traffic in the summer, waiting in the staging lanes at the drags, running hard on a road course. I did all the obvious things, replaced the rad, thermostat, installed a dual electric fan setup, new water pump, but it just got worse. It ended up boiling out of the overglow tank. Classic symptoms of a leaking head gasket. So I bit the bullet and replaced the head gaskets. That was the problem.

 

[iJimaniac]

Alright folks, time for some updates!
First of all, thanks for continuing to chip in! My power was out most of the evening (welcome to Arizona monsoon season), but I'm back up now, so here's my progress;

While my pump was off, I tested flow through the block with a garden hose. Pretty good. The same with the heater core and radiator.
Reassembled cooling system. Tested compression. All cylinders are the same since before overheating. All holding pressure. Next, I tested the fan clutch with the newspaper trick. I was able to stop it, although not as easy as some of the guys on YouTube did. So I'm thinking maybe this is it? Thinking about it, it would explain the better cooling at high rpms. I'm really hoping this is it, because if not, that basically leaves something internal in the engine.

 

[WarHawk-AVG]

The mix is mostly water at this point because I had to replace a lot of lost coolant with what I had on hand.

I'm gonna rout around the heater core tomorrow and see what that does. It blows plenty hot so I don't think it's plugged, but you never know...

The clutch fan seems good (no wobble), but I'll maybe look at that more too.

Fan clutch isn't wobble, it's engage or disengage (more or less free wheel), when radiator heats up it engages and fan more or less locks w/ waterpump shaft drawing air in, when cool it disengages to save HP from spinning that large air beater on the front of the engine

Run engine to operating temp, stop engine, see if fan is VERY difficult to turn by hand if easy, fan clutch might be worn out, have you chemically flushed radiator? Have you checked to see if lower coils plugged/clogged. (It can still flow ok, but lower coils clogged and cooling thru 1/2 the radiator or less, one way to test is after warmup w/ engine off lighly touch radiator fins, if hot all the way from top to bottom, they aren't clogged ) if you feel cold on bottom, hot on tip, might need to either replace radiator, or have radiator shop clean it out

Another overlooked and cheap fix, new radiator cap, AND good antifreeze (which in warm climates should also be called antiboil ), 50/50 mix under a good 13psi radiator cap can raise boiling point of coolant up to 265F, every PSI over sea level raises boiling point 2 degrees.plus is Antirust/corrosion of metal INSIDE engine

Also on water pump if very old and little to no antifreeze in coolant system can lead to pitting of the machined surface mating to the splines of the water pump, very low flow at idle, but at higher RPM it forces more water thru...

SAMSUNG say whaaaaaat?

 

[oldyellr]

Agreed. Those viscous fans are hard to diagnose. If there's more drag than there should be when it's supposed to be freewheeling, how do you know it's locked up when it's supposed to be? You can't really test that without doing damage.

 

[enjr44]

Well, I had the same problem with a 91 4.0. The temp gauge would go to normal and then some higher. When driving it would then it would drop and then go back up and just keep doing this. Back and forth. Found that the overflow tank would get higher as engine warmed up (all normal); but, it wouldn't suck the coolant back when it cooled (sometimes, not always). Replaced all the normal stuff (cap, thermostat, sender, overflow hose, etc,) with no change. No bubbles, no coolant in oil, etc. I just could not get the temp gauge to read steady

It was a blown head gasket. Found it when it finally overheated on my daughter and filled the crankcase full of coolant. Could have saved the engine if I had just taken it apart and fixed it to begin with.

 

[iJimaniac]

Sorry to leave y'all hanging for so long (dang live is busy), but basically here's how it's come down; replaced water with 50/50, seemed to pretty much solve the running hot. It still fluctuates very slightly, but not bad. Using it for my DD again, but I think I'm gonna trade for a less high-risk vehicle.

 

[enjr44]

Once the warranty expires, they are all "high risk" vehicles.