That's a touch hot...

[Rupert]

My truck, a '91 Isuzu Trooper with the 2.8L Chevy V6, overheated last night. The only sign that something was wrong was that the temp gauge was pointing to hot. Let's assume the engine is not permanently damaged. I want to know what can cause overheating. I popped the hood, and the coolant resevoir was empty. I did a cursory once over, and I didn't see any obvious leakage of coolant. I haven't checked the oil or opened the radiator cap yet. It was dark, so I easily could have missed something obvious. The upper and lower hoses to the radiator are in need of replacement. I'm going to go to class now, and I'll be able to deal with this later in the afternoon. So, what might be wrong given the little info I have? It would greatly help with my diagnoses!

[Speed_Racer]

Could it possibly be a coolant temp sensor? I had something like this happen in my old Escort. The temp gauge was all over the dial, past C some days, way past H otherdays.

If there was no signs of overheating, it could just be the temp sensor going crazy on you.

[ifcar]

It probably wasn't just the gauge malfunctioning if the coolant reservoir was dry.  

[SaltyDog]

So yesterday the coolant was full and today it's gone?

[Rupert]

Heh, I wish I knew. I doubt it drained all the way yesterday, because I only drove it for a mile or two yesterday. I suspect a slower leak, but haven't had a chance to look. Other than a leak, what could it be?

[cozmik]

I would make sure the cap is still in good condition and that there are no pressure leaks in the system. If the pressure of the system is different than what it was designed for, then that will change everything about how the coolant works at different temperatures.

Otherwise temp sensor sounds like a possibility.

[Rupert]

What does a bad cap look like? Do you think I could get it pressure tested for free? I checked the oil, and there's no coolant in it, so that's good.

[Rupert]

I filled the radiator and res. and ran the truck until it was warm. No white smoke and no really big leak. We'll see if there's a puddle tomorrow since I didn't see any super obvious leaks. I'm just gonna make sure to keep it topped off and keep an eye on the temp guage until I have money enough. I think it is the lower hose, but I'm not totally sure.

[SargeMonkey]

My truck, a '91 Isuzu Trooper with the 2.8L Chevy V6, overheated last night. The only sign that something was wrong was that the temp gauge was pointing to hot. Let's assume the engine is not permanently damaged. I want to know what can cause overheating. I popped the hood, and the coolant resevoir was empty. I did a cursory once over, and I didn't see any obvious leakage of coolant. I haven't checked the oil or opened the radiator cap yet. It was dark, so I easily could have missed something obvious. The upper and lower hoses to the radiator are in need of replacement. I'm going to go to class now, and I'll be able to deal with this later in the afternoon. So, what might be wrong given the little info I have? It would greatly help with my diagnoses!

The therma stat went out, happened all the time on our old corrolla. But why is there a Chevy V6 in a trooper? You might need to replace the coolent hoses, they can swell shut, and the radiator my have crud in it, making the coolent flow worser(Word choise?). Are you using 100% antifreeze? It helps, the water/freeze mix justs causes rust and does not move heat as well.  

[Rupert]

No, I'm pretty sure it's leaking from a hose. The Trooper came with three engines in '91. A small four, a larger four and the GM V6. It's like the late '80s-early'90s Chevy Novas that were really Corollas. Why would I use 100% antifreeze? It doesn't get to -100F here . I've heard good reasons for the mix, but I forget what they are. If 100% was best, that's what would be reccomended.

[SargeMonkey]

Think of it this way, we have always used 100%. We also get extremly high amount of miles out of very beatup and lously cared for cars. 300,000+ miles out of an '81 corolla that was hit in all four corners twice. We sold it for $100 and I still see it very once in a while. It gets about -10 here max, or is it min? Anyway when we use a mix of around 50% the engine in that car would boil over, same in the two trucks, and the camry in my sig.

[JWC]

According to Bosch's automotive engineering manual, ethlylene glycol coolant begins to lose its beneficial properties at mixes above 55%.

Other problems that can be encountered are:

lower fuel economy
water pump fatigue
wear on aluminum cylinder heads

[Secret Chimp]

My truck, a '91 Isuzu Trooper with the 2.8L Chevy V6, overheated last night. The only sign that something was wrong was that the temp gauge was pointing to hot. Let's assume the engine is not permanently damaged. I want to know what can cause overheating. I popped the hood, and the coolant resevoir was empty. I did a cursory once over, and I didn't see any obvious leakage of coolant. I haven't checked the oil or opened the radiator cap yet. It was dark, so I easily could have missed something obvious. The upper and lower hoses to the radiator are in need of replacement. I'm going to go to class now, and I'll be able to deal with this later in the afternoon. So, what might be wrong given the little info I have? It would greatly help with my diagnoses!

The therma stat went out, happened all the time on our old corrolla. But why is there a Chevy V6 in a trooper? You might need to replace the coolent hoses, they can swell shut, and the radiator my have crud in it, making the coolent flow worser(Word choise?). Are you using 100% antifreeze? It helps, the water/freeze mix justs causes rust and does not move heat as well.

That's not true. The best coolant is water. You need the antifreeze in there to keep it from insta-rusting the engine.

[93JC]

Are you using 100% antifreeze? It helps, the water/freeze mix justs causes rust and does not move heat as well.

That's not true. The best coolant is water. You need the antifreeze in there to keep it from insta-rusting the engine.

You silly bastards are both wrong. (with respect to what antifreeze does. Water is indeed one of the best coolants.)

Antifreeze is used to, you guessed it, STOP THE COOLANT FROM FREEZING.

Most coolant systems are designed to use a 50/50 mix of antifreeze and distilled water.

(colder places (I'm talking REALLY cold places: Siberia, northern Alaska, northern Canada, Antarctica) use a 75/25 mix, usually)

[Secret Chimp]

Antifreeze is used to, you guessed it, STOP THE COOLANT FROM FREEZING.

That's obvious, doofus. It also acts as a rust inhibitor.

[SargeMonkey]

38mpg out of a poorly cared for engine... We also don't have any cars with aluminum head me thinks.

[93JC]

Antifreeze is used to, you guessed it, STOP THE COOLANT FROM FREEZING.

That's obvious, doofus. It also acts as a rust inhibitor.

Not really, no. There's no reason whatsoever to add ethylene glycol into your coolant to prevent rust, unless you've poured salt water into it too.

Actually, ethylene glycol, over time, in contact with ambient oxygen, will break down into a few different sorts of organic acids and start eating away an engine block. Neat, eh?

[saxonyron]

You guys are missing the point that the ethylene glycol not only prevents freezing, but very importantly raises the boiling point to almost 300 F.  The old days cars, especially high-performance ones, would routinely "boil over" if they were running only water.  I remember reading an article about 20 yrs ago about a guy driving a 1963-67 era Vette.  After aggressive track driving, he had to run pure ethylene glycol because the engine would run hot and keep boiling over.  Can't quote numbers, but our 100hp/l engines run a lot hotter than the 40 hp/l dogs of the 1970's.