95 3.8 Overheating - Clogged Radiator? Fan?

[Longhorn2806]

Hi, I'm new to the forums, so pardon any newbie (possible & probable) etiquette

I'll try to be as direct and short as possible, but the symptoms are all over the place (SEE END OF POST FOR QUICK SUMMARY) :
I have a 95 mustang, 3.8L V6, manual. About 6 months ago the temperature started to swing from 1/3 hot to 2/3 Hot. While driving, it would continue to do this, but it would never overheat! I figured it was just the thermostat sticking, so i took my time to fix it. (I'm in grad school, so no tools or do-it-yourself options here)

I took it to a shop , and we found that the ENTIRE cooling system required 1/2-3/4gal of water. (Basically, it was empty...doh!) I am so used to the coolant getting checked when I take it in for an oil change, i never looked at it - Dumb, I know - please go easy; I beat myself up enough :-/

They did a coolant flush (which had to be done 3 times because of rust & crap coming out). Also did a pressure check on the coolant system - no leaks, everything is good. AFTER THIS, my car started to overheat. Not what I would expect with fresh, new, full coolant.

The symptoms are all sorts of convoluted, but here they are:

After the coolant flush:
The car would overheat, but I could cool the car down by gassing it to ~2k RPM. (Hold @ 2K RPM until The temp would swing from HOT to middle / just below). At idle, it doesn't overheat. I would drive it further, the temp would eventually go up again - I would gas it to 2k RPM until the temp came down - repeat. It would do this in stop & go OR highway driving. (It seems to revolve more about what RPM's the engine is running at than the actual speed)

Trip #2 to Mechanic:
- Replaced the thermostat; If continues - next thought is possible radiator clog.

The car seems to stay cold for a long time (~5-10 minutes of driving), and then quickly creep back up to HOT. NOW, it seems like it doesn't get as hot as before - only goes to just below the "H"...but this could be because I gas it to cool it down before it ever gets there. The strange thing, besides it still not working, is that NOW it is HARDER to get it to cool down. I have to gas it to ~2300 - 3k RPM, and the temp swings to just above middle.

A VERY interesting note on the fan: From the little I have driven the car since the overheating started, it seems:
- When initially starting and driving the car, the fan will come on once temp reaches just above middle, and turn off when temp reaches just below middle, as expected.
- After a while of driving the car, it seems especially on the highway, the fan WILL NOT come on anymore (idle or not).
- If I turn the AC on (while idle), fan comes on.

Any suggestions or comments? I feel like the next steps are:
1) seeing if we can clean out the radiator with chemicals
2) new radiator
3) New fan?
4) Possible new CCRM? (from what i read, i don't think this is the case, as the fan ALWAYS comes on when the AC is on, and the FAN comes on when required if initially idling. But maybe high-speed fan resistor?)

So, sorry for the book: In Summary:
- I can cool the car down by Keeping the RPM's in between 2K-3K for 15-25 seconds.
- It seems that the fan works when the car is initially turned on, but not after driving for a while or at high speeds (50-70MPH'ish).
- Possible Radiator clog?
- Does a fan make THAT much of a difference when driving on the highway, or does this point more towards the radiator? (remember, when idle & No fan = temp doesn't rise; just stays wherever it is at the moment)
- How much of a temperature swing is normal? I assume it should stay in the middle, with a little bit of give. (not my insane " H....swing down to 1/3 hot ")

Again, no tools myself, but I want to get opinions from everyone before continuing to let the mechanic guess & check at my expense :-/ (Trustworthy guy, but 2nd opinions never hurt).
anything else to be thinking about that can affect a car to overheat?
Thanks so much!!

 

[94GTMustang5.0]

is the air deflector in place? These cars came equipped with an air deflector on the bottom of the car that helps pull air over the radiator. I know its more essential with the fox body mustangs, but it couldnt hurt to check.

Have you verified the temps with an infrared thermometer?

 

[Longhorn2806]

Hey 94GT,

Thanks for the hint - Yes, the deflector is connected to the underneath of the front bumper.

I haven't done the infrared, but when i talked with the mechanic, he said that they found warm and cold spots in the radiator, so this is a sign of clogged pipes.

I guess overall, I find it hard to accept that a radiator would be so clogged that it creates a TERRIBLE backup...but I guess its possible. Maybe others can comment on how often this happens.

Also, I just wanted everyone's opinion to the possible causes for overheating - Either the coolant system (radiator, thermostat, & water pump) or the fan. Anything else that can cause overheating?

Thanks again!

 

[divit250r]

Sounds like the same problems my mom's 3.8 Thunderbird had. Head gaskets kept taking a dump, apparently a pretty common problem for that engine, since it shares the 302 / 5.0 headbolt pattern and style.

Her car would put out no heat, constantly lose coolant, and smell like antifreeze all the time. The dealer replaced the head gaskets twice and when it was ready for it the third time, she traded it off on an Escape. lol

Hope it's not your problem, but it's something to investigate at least.

Scott

 

[Longhorn2806]

Hey Scott,

Ironic you say that - ~9 years ago, my head gaskets did blow. Long-story short, FORD had an issue, so i got reimbursed, new head gaskets, etc..

Overall: I know the symptoms of head gaskets blowing (which is white smoke out the tailpipe & a VERY SHAKE CAR!) haha

Another possibility I found was the heater block may be clogged...but I don't think this is the case, as no coolant is put through the heater unless it is ON. (and all of this is happening when the heater is NOT on).

Again, thanks for the thoughts!

 

[Longhorn2806]

Any thoughts on the temperature sensor just being bad?

The engine has never smoked, and it got VERY VERY close to "H". Personally, I think the wild swings in temperature still point to the radiator, but thought I would throw it out there for thoughts. What usually happens / what usually indicates when a temp sensor is bad?

 

[Chythar]

You can have a head gasket leak and not have any white smoke. My old 94 V6 blew a head gasket (chronic problem on that 3.8l engine) and it let exhaust get into my coolant. Car would overheat much like you described. No white smoke, no sweet smell to the exhaust, and the engine ran just as it always did. But the exhaust pushed coolant out of the system causing the engine to heat up.

To check for exhaust in the coolant, pop the radiator cap when the car is cold. Look for dirt or grime in the coolant. It should still be decently green since you just got a flush. Exhaust in the coolant will leave the green with streaks and spots of what looks like dirt. If the coolant is brown, you've got a major rust problem.

Additionally, since you just had the coolant flushed and filled the cooling system should be full up to the filler neck. If it's low, there's definitely a problem (duh).

Next, leave the cap off and start up the car. Look for any bubbles coming up, they're usually small bubbles. That's exhaust in the coolant.

Another thought for you. All 94-95 Mustangs, except the 94 Cobra R, share the same radiator. Over time, flex in the Mustang chassis ends up cracking the radiator on the driver's side. Sometimes this crack is small enough it only leaks when the car is at operating temperature. Any leaked coolant evaporates off and is never visible.

There are two temp sensors on our cars. The V6 and V8 use the same sensors, just in different spots. The ECT sensor is used by the computer to determine engine temp. If this sensor is bad, the computer may stay in a warm-up state all the time. This mode shuts off once the engine reaches operating temperature, but if the ECT is bad this mode never stops. Had this happen to me as well. I had to buy a $200 code reader that lets you do live engine monitoring. One of the values shown was the engine temp, and it was jumping all over the place.

The second temp sensor feeds the dash gauge only. So if you're actually overheating this sensor is likely OK.

 

[Longhorn2806]

Thanks for the thoughts!

 

[Longhorn2806]

Got the car back with a new radiator - seems to have been the problem. The mechanic said it was pretty badly clogged. Temperature sensor is OK.

Thanks for the thoughts!

 

[Longhorn2806]

My apologize, but back with an update (Radiator didn't totally fix it).

What happens now:

Cold weather: Drive it ~45/50mph for ~8-10 minutes w/ rpm @ 1500 = overheated. Brought the temp back down by raising rpm's to 2000 at a stop light (manual car). Freeway driving: swings from 1/3 hot to 2/3 hot, then swings back down (3-4 seconds for the swing)

BIG UPDATE: Today, we had 75/80 degree weather! (live in TX). The car ran PERFECT! In city traffic, temp would get to 2/3 hot, fan would come on and bring it back to middle temp level. On the freeway, the temp stuck around 1/2 way or just below. NO TEMPERATURE SWINGS.

Recap: I'm not losing coolant, i have a new radiator & thermostat, and the fan kicks on when its supposed to. Why would these swings & overheating happen only when its cold (30-50 degrees)?

Thoughts from the mechanic:
- Water pump might be going bad, but is OK after it heats up.
- Possible Faulty temp sensor for my dashboard gauge.

My Thoughts:
- I think the temp sensor is bad, and the cold weather affects the wires and resistance. -> However, once the engine heats up, the probe should be the same temp. Also, when it overheats I rev the engine to 2K -> unless this slightly rattles the sensor (doubtful), the temp just slowly comes back down. It doesn't immediately jump, which i might expect if a wires is faulty.
- Might be an air pocket in the system --> Wouldn't this show & cause temperature swings on a warm day as well?
- Water pump may be failing -> again, shouldn't this show regardless of temp outside?
- Bent hoses? again, didn't do anything to the car -> should show in warm weather.
- Head gasket leak -> I don't lose coolant, the car idles and runs OK, no smoke out the tailpipe

Thoughts? Thank again in advance!

 

[mbychows]

It seems to me that the CCRM is doing what it's supposed to do regarding the fan...it turns the fan on if (1) the coolant temp at the sensor rises above 221 F, it then turns it off when it drops back below 200 F, or if (2) the AC is on and car is below ~45 MPH. So that seems to check out. I had an issue with my fan ground corroding out a while ago, and my fan didn't come on at all...as long as I was going above 35 MPH, I didn't have an issue with overheating. I guess that relates more to your comments in your first post, though.

Anyway, if it were me and a mechanic narrowed the issue down to my water pump or the dashboard temp sensor, I'd just replace the sensor myself first. They're cheap and it seems like a decent place to start just to make sure you're getting a reasonable estimate of the engine temperature.