Random temperature jump when stopped

[Dubious_Downfall]

1993 Manual Ford Explorer 4x4. Rebuilt motor. Trying to figure out the cause of my random temperature spikes when I stop at red lights.

It only seems to jump at idle RPMs, after reaching operating temperature. It jumps to about 3/4 of the gauge on my dash. It usually rests right at the "L" during this cold weather. It only lasts less than 5 seconds, then drops back to operating temp. Immediately after the temperature jump, the hose running to the thermostat doesn't feel very hot unless I give it a few squeezes, which makes me think there's either a big bubble in the system, and/or air is being sucked into the coolant system somewhere. I know it does it with the heater on, I need to see if it does it without it being on. No leaks from anywhere. Heater works fine. The motor runs like a top. The only other issue I'm having is with my clutch, and I don't THINK the two would be related, but I'll leave that info here just in case. I have another post explaining my clutch issue. It may also be worth mentioning that I always warm up my truck until the tachometer settles at the usual spot (About 600 RPM in my Explorer)

I am not the owner that rebuilt the motor, so I'm going to presume that the cause of my temperature spikes is the same thing that caused the original owner to need an engine rebuild. So I'll rule out the water pump and thermostat for now, as they likely were replaced during rebuild.

Thanks in advance, guys!

 

[1993Saturn]

I put this comment in thread on Goofy Temperature. It applies here too.
"
I would suspect that due to the famous Explorer air bubble. The coolant doesn't always conveniently fill up all the nooks and crannys of the system. There can be a big bubble in the heater core which can sometimes cause a thumping there. There can also be one over the thermostat where the temperature sensor sits. When the coolant fills the void, the temp reads normal. When the bubble appears, the thermostat is now sitting in hot air and the reading skyrockets. Ford long ago had secretly offered a solution with a bypass hose from the top of the manifold meeting up with the pump return hose to the lower radiator. No longer available, hence we must suffer with this particular quirk. I had installed a Prestone heater hose "T" in the upper heater hose. It has a lawn hose threaded cap on it used for flushing. It also worked well with filling up that void when refilling the system. I badly discovered you better replace it every year and a half or so or it will blow apart in about 2 years."
Those bubbles can be real annoying and can persist or just show up at random unannounced.

 

[Dubious_Downfall]

Any video, pictures, or instructions on a DIY version? I saw that thread, but the lack of information is what led me to ask here. I also didn't want to assume my symptoms are from the same exact cause without being open to the possibility that it's from somethimg else. Thank you for the response. I'm really hoping you might have a little bit more info on this.

 

[Dubious_Downfall]

Looking into how to bleed air from a cooling system. I'll report back if it works or if more measures needed to be taken.

 

[1993Saturn]

I'll tell you later. Rather tied up right now

 

[Dubious_Downfall]

I turned on the heater and got it warm enough to start "overheating", squeezed the hoses until they were full of coolant and I couldn't feel any air in them, then let it cool overnight. Before starting it, I filled the radiator until I almost couldn't put the cap on without causing coolant to spill over. Then I squeezed the hoses again, just to be sure that they were filled with coolant. After that, I started the truck and let it warm up. When it was warm enough that I could be fairly certain that the thermostat had opened, I revved the motor up to about 3,000 RPM and kept it there for a solid 15 seconds.

After that, I drove to work, let it cool, checked the radiator, filled it to the brim again even though it had only gone down by less than a cup of coolant, and now I'm keeping an eye on it whenever I drive. I haven't seen the temperature go up significantly at all since doing what I tried. Hopefully that's the end of my issues. You guys will know if it isn't.

Thanks guys!

 

[smegun]

fan clutch is supposed to get viscus when hot symptoms of bad fan clutch is loose goose when stoped its overheating?

 

[Dubious_Downfall]

Yes, it is overheating. I spun the fan while it was cold. It seems to be fine. I've replaced a couple fan clutches. I know what they're supposed to feel like and how much they're supposed to spin freely.

However, I had to jump my Navajo the other day... While the hood was open on the Explorer and it was idling for 5-10 minutes, the radiator cap and coolant reservoir started spitting out coolant. I thought about it and realized that a bad cap could be spitting out coolant and letting air in, as well as lowering pressure in the cooling system, causing the coolant to boil at lower temperatures. I ordered a Motorcraft OEM cap. Part number "RS90" for anyone who needs it.

It would 100% explain how air keeps getting back into my cooling system even though I've repeatedly bled the bubbles out.

I'll be back with an update. I might replace a couple of cooling system parts pretty soon as well. It depends on if the temperature still fluctuates after a new cap.

 

[Dubious_Downfall]

I no longer have coolant spewing from my radiator cap and/or reservoir. But my truck still overheats.

I squeeze the hoses when it's warmed up and idling, and I can feel that the hose going from the radiator to the thermostat is not fully filling with coolant. Even after squeezing it and getting it to fill with hot coolant, I can feel it empty out and not refill. I checked the hose going from the pump to the radiator, and that hose is nowhere near as warm as the hose coming from the radiator and going to the thermostat. I can't tell if the pump is pumping water or not. But normally I can rev the engine about 500 RPM above idle and the temperature gauge will drop fairly quickly. Which makes me think that the pump works, but there might be a clog somewhere, keeping the system from sustaining pressure.

My guess at this point is that the radiator is clogged. I'm going to try to feel around it for cool and hot spots next time. I may also take my belt off and double check that the water pump doesn't have any noticeable "play" by trying to wobble it around a bit.

Any advice on checking if a radiator is clogged would be appreciated. I've replaced a radiator on my Navajo before. But I've never dealt with a clog.

At least I seem to be narrowing down my possible causes. I'll be back with more.

 

[Roadrunner777]

Check for temp difference on either side. You can get cheap non-contact IR gauges for that, darn useful for lots of other stuff too.

 

[donalds]

Cracked head ..head gasket maybe

 

[Dubious_Downfall]

Cracked head ..head gasket maybe

I'd have to be pretty clueless to not be checking my oil and coolant constantly. Neither of them have any significant changes. And my cooling system doesn't seem to be leaking at all anymore. It's always full and the reservoir level doesn't fluctuate unless running.

In response to RoadRunner: I might actually have an IR laser thermometer somewhere. I hadn't remotely thought of it. Thank you.

The bright side is that a new radiator for a manual transmission Explorer of my year is only about $50 on Rockauto at the cheapest, and I would have eventually replaced it anyway. It's easy, and if you have one of these trucks with the original radiator, you really should replace it. Hell, basically the whole cooling system should be aftermarket by now. Otherwise it will eventually break somewhere. My problem is not having space to do repairs when I need to. Otherwise I'd be replacing things first and THEN asking what's wrong when I inevitably screw up at some point. Lol

Thanks for the help, RR.

 

[BKennedy]

I recently replaced the radiator for the 3rd time, this time with an all aluminum unit. I did this because I wanted to eliminate a possible failure point with the plastic/aluminum units because sometimes I am a long ways from a paved road and a tow truck. If you lived closer, you come pickup my old radiator and try that one. Its very well made, the thickest one available but about 10 years old.
My fill procedure is as follows; After I dump 1-1/3 gallons of concentrated anti-freeze into the radiator, I start the engine with the heater on. I immediately top off the radiator with water, ends up being about the same amount as the coolant. I leave the radiator cap off. Once its full, I wait until I feel heat in the upper hose which indicates the thermostat is open, then start squeezing it with both hands. That pushes the air out. Top off the radiator, go for a drive.

Have you tried flushing out the radiator? Do a flush, then find a steep hill to drive up and down. If there is any air in the system that should push it out. One of my old houses had a very steep driveway. I used to fill the coolant system with the Explorer facing up the grade and I never had to pump the air out.
How long has this issue been occurring? Did it just happen, or did you do something with the cooling system?

 

[massacre]

When I worked on heavy trucks, I bought a snap on airlift setup to fill coolant. Now I use it for everything.
It basically pulls and holds a vacuum on the entire cooling system using shop air.
Then you can hold the vacuum for like 15 min to see if there are any leaks before filling it with coolant. This can be a time saver VS filling it and running it and then finding the leak.

Also because it fills the system under vacuum, there is no “air trapped in the system” problems. Don’t have to wait for thermostat to open, and coolant level to drop, then add more coolant. Again because of the vacuum.

The tool was very expensive but at the time I used it almost every day and it saved so much time and hassle. Those trucks have like 5 gallons or more of coolant, so much quicker than using a funnel lol
Now I use it on many other vehicles and it still saves a lot of time.

 

[RickOTR]

The only way I found to get all the air out of my cooling system was to vacuum fill it. This is how Ford does it at the factory. I rented the vacuum tool from AutoZone and used my own shop air. Fast and easy...

 

[Roadrunner777]

If you can replace a 20+ year old radiator with a $50 part... I guess that's a pretty obvious thing to do, even as preventative. I would also replace every coolant hose that you don't have history on... now's the time. Also... this would be the time to inspect the fan for cracks (there's a sticky thread on this chronic problem), maybe the fan clutch, serpentine belt, idler and tension pulley, and... well, basically anything on the front of the engine that you don't have good history on. Or not. I mean, I like to work on my vehicles just for the therapeutic value. But, if you want a problem-free engine for a while, do the easy stuff when you have the best opportunity. IMHO.

 

[BKennedy]

I replaced the entire cooling system in the Explorer several years ago. This time, when I just changed the radiator I replaced the thermostat, both hoses, and that heater bypass vacuum valve because I had one fall apart on the trail (I have a piece of copper tube in the center console to use as a bypass now). Heater hoses are about 5 years old and look new so I left them.

Many years ago, I found cracks in my fan when replacing the water pump and fan clutch. Bought a Motorcraft replacement from Ford because if the fan goes while spinning, it takes out everything nearby.

Easy way to check water pump and fan clutch are to grab the fan and give it a wiggle. Should have little to no play.

 

[Centaurious]

A) Make sure that your thermostat has a bleed hole in the flat body. B) Make sure that your radiator cap is at least 16lb or more, 14lb will allow air pockets to form. C) put the truck up on ramps or a very steep hill while filling with coolant.