Hey guys. I've had the oddest problem with my 'lude lately.

Starts off a few months back when I was having overheating problems. 6 mechanics later, I've gotten 6 different opinions and fixed half a dozen different things. Head gasket has been replaced, radiator flushed multiple times, thermostat replaced, fans checked and all set to go.

But, things are still overheating. I searched a bunch of times and kept seeing problems with grounds, so I checked all my grounds. I drove from Tucson to Phoenix a couple days ago, and I didn't have any overheating problems! I figured that maybe it WAS my grounds, but when I was almost there suddenly my dials were freaking out. Turns out my alternator was unplugged. So, I plugged it back in, and now my battery is good to go.

On my way home, same overheating problems, but now I know my alternator is plugged in.

I brought it to Checker to have them test my alternator, and it turns out that it's kind of low. It works, but not really well. Also (idk why and it's freakin' me out) but it is putting a load on my engine! If you unplug it, it idles normally, and when you plug it back in suddenly the RPMs jump down a few hundred.

Could my alternator be the reason for my overheating? I go from the "middle" to "3/4" all the time, but it's only at 70 MPH or higher, but that's highway driving so it's going to be hard to get back home if I can't drive on the highways haha. When it gets to 3/4 I just turn the heater on full blast and slow down to like 60 and the temp usually goes back to normal, but I can't drive 60 on highways all the time. People get pissed.

So yeah.. I'm supposed to drive back to Cali in a couple days for Xmas, and not sure if I should if I'm gonna keep overheating!

Any ideas?!?!?!

 

If you can resolve the overheating issue by putting on the heat and slowing down, your car is clearly overheating and is not just a malfunctioning gauge or temp sending unit.

As far as the alternator, if it's malfunctioning, it could be trying to create max power all the time, which will put more drag on the motor.

It seems unlikely, but it could be putting enough stress on the motor to make it work hard enough to start overheating when driving on the freeway. If it's not working well and you need to replace it anyway, I would start there before doing more with your cooling system; start with the problems you know.

 

Another thought - if the engine is running too lean, it will cause a dramatic rise in head temperature (and therefore engine temp.) Normally, the engine runs somewhat rich. The excess fuel carries some of the heat away and the excess fuel hits the catalytic converter where it burns up any excess oxygen.

I am not an engine authority - but there are only a few things that I can think of that would cause the engine to run normally, but overheat.

1. Not enough coolant.
2. Blown heat gasket. - I take that you have checked these two items.
3. Plugged Fuel filter - unlikely as engine would have difficulty maintaining high load for more than a few seconds before sputtering badly or seriously loosing power.
4. Bad Oxygen sensor causing a lean burn.
5. Bad MAP sensor causing a lean burn.

Both of the last items are used by the ECU to calculate fuel mixture. If the alternator is a problem, it would most likely overheat the alt., fry the battery and catch wiring on fire if there was a short. I think your alt. is ok if you haven't had any other weird electrical problems.

Does anyone else have another take on this?

 

Ok, if the alternator isn't working intermittently, because the brushes are bad or whatever, then intermittently the system voltage could drop below a functional level. All the voltage dependent sensors could be affected. Are the head lights dim at night when you experiance the over heating on the high way?

Check for soft, collapsed or kinked radiator hose. If the hose is just too soft (gets softer when its hot) then at high RPMs (like highway driving) the water pump can suck the hose until it pinchs shut and you'd never know it cuse it may only happen when you are crewsing at 3,000 rpm for a while. This effect can be master-errrr i mean, exasterbated by having blockage in the radiator. If there's blockage then the engine really is sucking threw a straw and a soft hose could suck shut. Now, if only my girl friend did that.

 

How can a head gasket make an engine overheat?

 

It's def not the head gasket or coolant. Replaced both already too just for good measure. The radiator hoses are fine too, and I am not having any electrical problems except for one time when the alternator was unplugged and everything turned off haha.

Not sure about the running lean thing... how do you check that?

 

check the spark plugs. A properly running engines spark plug should have a brown or reddish colored electrode. If the electrode is black, the car is running too rich. If its white, its running too lean. http://z.hubpages.com/u/214665_f520.jpg

 

Well, i had the same problem before. I took off my thermostat.

 

My sparkplugs are doin' fine.

How would taking off the thermostat help though? It's working just fine, and I'm not overheating when the engine is cold...

 

It sounds to me like you just have a stopped up radiator. Flushing the radiator doesn't do much besides getting the old coolant out and new in. If the radiator is stopped up flushing it will not help. I have taken radiators apart before and not even been able to push a metal rod through the tubes. You might need to replace it instead of just flushing it.