intermittent overheating

[dlnelsonroca]

Hello! I have what's probably a simple problem, but I need your expertise to really know what to do. Here's my issue:
I've recently had the engine rebuilt because of a bad overheat. All original parts and the inexpensive labor here in southern Mexico. I am having a catalytic converter brought here in a few weeks because we couldn't find the right one here. So the mechanic here put in something else in the meantime. The code came up a few days later of P0420 catalyst system efficiency. Since then I've gotten two other codes, P0013 and P0014. I mention these jsut to give all the background possible, although they're not my chief question right now.
A few days ago the car began to overheat. I had the AC on, but turning it off didn't change anything. I drove home, about a half hour, and as long as I was going quickly the temperature stayed normal, but as soon as I slowed down for a speed bump or went slower than 50 mph, the temp gauge rose quickly. I ended up turning it off about a half mile from my house, and getting it later after it cooled off.
The water pump doesn't wiggle, and so I assume that it's okay. The coolant looks good as well, and appears to be half coolant, half water, although I can't tell for sure. It's bright green.
Now the mystery to me is that since then I've driven it all around my little town, letting the heat go to nromal temperature, and with the AC on, and no overheating. I haven't dared to drive anywhere farther for fear of overheating. I almost wished it would overheat again so I could check to see if the fan was working, but it is working in town.
Is this the thermostat beginning to fail? Or something else. I need to k now so I can order a new one from the States with someone who's coming here in two weeks.
Thanks!

 

[Wooluf1952]

You should've heard the fan if the engine was overheating and the fan was working. It would've sounded like a jet engine.

 

[AWD V8]

A bad thermostat is the first thing I think of when operating temp is inconsistent. Only use an OEM thermostat.

The above is assuming that you do not have air trapped in the cooling system.

 

[gmcman]

What temps are you seeing when it's overheating? Are you sure the coolant is topped off? Did you mix green antifreeze with the orange dexcool?

A remote possibility is a bad head gasket introducing bubbles into the cooling system but hopefully that's not the case.

 

[Mooseman]

Apart from the above, test your fan clutch. Also check the relay for it.
How to test the electro-viscous fan clutch

 

[dlnelsonroca]

Thanks! I did the check on the fan at operating temperature. I could stop it with a rag, and once stopped it was easy to hold stopped. It looked almost exactly like the video posted above. Does that mean it's good or it's bad?
The motor was all apart, so the only coolant in it was new and green.
I don't recall the fan sounding like a jet engine at any point.
Right now when I tested the fan and then turned off the motor, I heard a sound from the coolant reservoir like a popping bubble about every two seconds, not boiling, just a pop, and the water in the reservoir would move a little bit.
I haven't taken the car outside of my village since the overheat, and idling in town hasn't overheated it again.
Any way to figure out what's up with these new clues?

Also a slight hissing from the same general area while it was popping.

 

[Mooseman]

That would mean the fan clutch has failed and probably the reason for the overheat. Our favourite replacement is Hayden. Dorman are hit or miss like most of anything from them electrical.

The popping is probably the cap releasing pressure to the reservoir tank as it gets hot. Normal and would become worse as it overheats.

 

[dlnelsonroca]

That's good to know! I've just ordered a Hayden fan clutch from Rockauto. It will be nice to drive on the road again without worrying about overheating!

 

[mrrsm]

If you are doing the Fan Clutch R&R yourself... One of our Members... @Matt ... has penned a Write-Up on "How to Replace The Water Pump" that has an absolutely Brilliant and Simple way to secure the Water Pump Bolts in a manner that will make removing the Fan Clutch Nut a breeze to perform:

http://gmtnation.com/forums/threads/how-to-replace-the-water-pump.15639/#post-505126

 

[gmcman]

I'm not doubting that the fan may be bad, but if there was green coolant....are you sure all the orange dexcool was flushed out?

I'm pretty sure the green doesn't mix well with the orange, not 100% certain if that can cause it to gel up.

If you disconnect the coolant temp sensor, the fan should lock up and fully engage as a safety default....does it?

 

[Matt]

I'm not doubting that the fan may be bad, but if there was green coolant....are you sure all the orange dexcool was flushed out?

I'm pretty sure the green doesn't mix well with the orange, not 100% certain if that can cause it to gel up.

That's exactly what it does. If you go to green coolant, you need to completely flush the block, heater core etc to make sure there's no residual Dexcool.

 

[xavierny25]

I'm a +1 on you can't mix the Dexcool and the green stuff. Although my issue was with my 06 RR sport at a local jiffy lube they add the green coolant to top off and the reserve rank expolded about 20 miles later. Of course the jiffy lube place covered the repair and a rental for 2 days.

 

[dlnelsonroca]

Hello again! I replaced the fan clutch, and it seems to be working great now. There is a problem still. The symptoms are that after I drive about forty minutes then at a stoplight the oil gauge sometimes goes to 0 and the engine temperature begins to go up immediately. If I rev the engine a little bit then the oil gauge goes normal again, and the engine temperature goes back to normal. This doesn't happen when I make fifteen minute trips.
I do remember that the oil gauge did the same on occasion, but rarely, before rebuilding the motor. So I think the problem has been around for a while.
So I'm wondering two things: 1) Is the oil pressure switch faulty, or is it the oil pump? 2) What are the symptoms of a leaky head gasket?
I ask the second question because when I got the fan clutch replaced the mechanic said that the water was quite low. The oil looks good, but he said the head gasket may be leaking. And I read that this could cause overheating when air bubbles get trapped in the cooling system.
Thanks for your help once again!

 

[Mooseman]

Are you also getting a message or idiot light for the oil pressure? If not, I'd suspect the stepper motor for that gauge, as well as for the temp. To confirm both, use a Bluetooth ELM327 OBD adapter and the Torque app (Android) to see actual readings from the sensors. If it is really going to 0 and getting bells/lights, 99% of the time it's the pressure switch. Replace it and see what happens. Not too pricey so it's a cheap fix.

If the head gasket was bad, there would be hell. Water in the oil is the most apparent symptom. You could check each cylinder with a borescope for a clean and wet cylinder or two as well as a clean spark plug and you would get the sweet smell of coolant in the exhaust. Compression test would also concur with any other findings.

 

[dlnelsonroca]

Thanks! I changed all the gauges a few years ago when my fuel gauge started messing up, so I don't imagine that the gauge itself is the problem, especially when the temperature goes up the same time as the oil pressure gauge goes down. Once a few weeks ago it got hot enough for the water in the reservoir to boil, so I think it really did get over hot. The only gauge that lights up when the oil pressure appears to drop to 0 is the check gauges light. And then it goes off as soon as the oil gauge goes up again. It would be great if the problem were only the pressure switch! Would that explain that the car getting hot when the oil pressure seems to drop? If so then I'll find a pressure switch and get it in as soon as I can get one here from the States in a few weeks. Hard to get good parts where I am.

 

[Mooseman]

I don't think the two are related. If it did overheat, I would recommend replacing the thermostat as they can be damaged when overheated, whether it was at fault or not. It could just be a coincidence that when going idle, pressure drops, causing the switch to fail, and the temp goes up, possibly due to the t-stat.

 

[dlnelsonroca]

Well, I finally got the parts from the States here, and they're all in the car. It was a real disappointment today when I saw the oil pressure gauge drop to zero again, even after I've changed the oil pressure switch. It only does it when the car's good and warmed up, and idling at a dead stop. Does this mean that the oil pump is probably going bad? Thanks for your advice!

 

[Mike534x]

My first Envoy did the same thing, only when it was at operating temp. Never did find out why, it never knocked or anything so I just let it be. Only way to tell if your pressure is really failing, is if you hooked up a mechanical gauge to the port where the pressure sensor plugs in and watch the reading.

 

[mrrsm]

Please tell us that when your Engine is at Idle... That you do NOT hear any noises like THIS:

 

[dlnelsonroca]

Thanks for the answers! I've only been inside the car when the oil pressure drops, but I didn't hear any odd noise at all. I put it in neutral and rev the motor a tiny bit, and the gauge jumps up. Once I get moving again it's fine. It's done this occasionally for the last few years, but it seems to be doing it more often now. I hate the thought that I or my wife might be somewhere and the oil pump quit altogether.

 

[Tiggerr]

I'd get a mechanical gauge on it pronto..wouldn't chance grenading the motor over it...
Way easier to swap an
Oil pump and pickup tube than swap a motor...

 

[gmcman]

I'd get a mechanical gauge on it pronto..wouldn't chance grenading the motor over it...
Way easier to swap an
Oil pump and pickup tube than swap a motor...

I agree on verifying oil pressure. ....but since he has 4WD.....could be splitting hairs on swapping motors. Since the front cover needs to be removed to release the pickup tube if I'm not mistaken, which is in conjunction with removing the oil pan.

Just throwing out some bad humor as both jobs would be a major pita.