My wife's van is really trying my patience lately. The A/C had been acting up, going in and out a little bit the last couple weeks, so I picked up a massively overpriced recharge bottle with the gauge to see if that was low.

She came home and parked the van, it was obviously at operating temp as it had just been driven. I connected up the guage and bottle and turned on the car with the AC at full blast, blowing warm air, though sometimes it blows cold.

The pressure reading on the recharge bottle was DEEP into the red zone, showing pressure around 150. I assumed that the compressor wasn't clicking as I know that can cause higher pressures.... but I also figured at this point that low refrigerant was not the problem.

I left the car running and went to the drivers seat to cycle the AC on and off a few times trying to get the compressor to click on, but it never did. After a few minutes of messing with it I started hearing a hissing sound and notice fluid spurting from the over flow reservoir cap. A quick glance at the temp gauge showed it was absolutely pegged. I checked the radiator fans and they were spinning, so I buttoned up the hood and took the van out to get it moving and drove around the block a few times.

During this drive, at one point, the temp gauge in the dash dropped to the OFF position for about 30 seconds and then snapped back to pegged hot. During this drive I had the heater cranked full to try and help cool it down. It was blowing hot air as it should.

After a couple laps around the block the temp wasn't falling much per the gauge so I took it back home and parked it and shut down the engine but left the key in the on position, thinking the fans might stay on. They didn't.

Pulled the code and I got a P0117 - ECT low voltage.

Also of note: Later on I turned it back on and the dash gauge indicated normal operating temp. I clicked on the AC and it started blowing cold and the temp gauge was steady. After about 30 seconds of blowing cold the AC air went warm and the coolant temp starting rising fast, so I shut it back down.

Ambient air temp during all this was north of 90 degrees.

Prior to leaving for work this morning (around 4:30am) I started it up and the AC was blowing real cold and coolant temp went up to normal and stayed there. I didn't have time to let it run more than about 7 minutes but during that time all, including the AC, as normal.

I've read that P0117 can indicate a bad ECT or bad wiring, but would that cause this overheating issue as well? Or is it more likely that the P0117 was triggered due to the actual overheating to the point of boiling and it was a valid reading? That is my gut feeling EXCEPT for the one little moment where the dash gauge dropped to the off position while I was driving. That makes me think of an intermittent short in either the wiring on the sensor itself.

My plan is to go home and pull the sensor and test it. I can check the resistance easily enough at ambient temp and then watch what happens when I hit it with a heat gun.

I also figure I can check voltage coming from the plug for the sensor while the ignition is on... I've read it should be about 5vdc. Lastly, I can check for a closed short in the wiring, I think.

Hopefully the sensor itself tests closed or open... Either would indicate a problem, but I don't think it will be that cut and dry.

And I'm left with the question: Can a fault in the ECT/wiring RESULT in sudden overheating, even if the fans were spinning? That doesn't quite seem logical. If not, what caused the overheating? It seems to be linked to the A/C somehow.

Really growing weary of this dang van.

Qwick, easy ,and cheap? Change the sensor. All your symptoms can be caused by the ECT sensor sending misinformation to the Pcm. Fans were spinning but were they spinning at correct speed?

Sounds like a likely cause of your issues, without the code I'd say thermostat.

Thanks fellas. My plan was to pull the old one out this afternoon after work and test it a bit and likely change it out no matter what as the problem seems somewhat intermittent. It's less than $20 and looks to be very easy to accomplish. I just wasn't sure if the overheating was a symptom of the faulty sensor or if the overheating triggered a valid sensor reading.

I looked at how to change the thermostat on youtube... much more involved so hopefully that isn't it. Plus, having witnessed boiling over at the reservoir tank cap I think that means the thermostat is not stuck closed, so likely it is ok.

And yes, fans were spinning, and they were kinda loud, but I have my doubts that they were running wide open.

Check and be sure that your radiator cap is good( the 2 rubber seals are in good shape), and is sealing the radiator correctly.

Be real careful with overheated engines and radiator caps. I had a not too bright relative remove a cap on a hot engine, got sprayed all over with boiling antifreeze and spent some time in the hospital. Turning off a hot car and letting it cool may be a better strategy that trying to drive it cool. Stick a box fan in front of it if that makes you feel any better.

Replaced the ECT... the easiest fix/replacement I’ve ever done on a car... but still had the issue. Was ok for a minute or two then AC started blowing warm and engine temp started climbing fast.

I scratched my head for a minute and realized that no coolant came out when I pulled the old ECT. That shouldn’t be, I figured. It should have lost some.

It took about half a gallon through the “radiator” cap. Reservoir was empty. When it boiled over yesterday i must have lost too much.

Seems to be working now. The next few days will tell.

Still acting up some but not to the sane extreme. I was watching the live data on my scan tool and as soon as the ECT temp hit 220 the AC stopped blowing cold and engine temp began to rise pretty quick. It got close to deadline but not there. It probably would have. All this was at idle. I goosed the gas for a little bit and temp started to flutter back down, kind of back and forth. Until it hit 220 again. Then it dropped steadily back to normal (about 211) and the AC went cold again.

Is there a chance the thermostat is failing and sticking partially closed, causing temp to rise, which results in the computer shutting down the compressor atb220?

If you didn't bleed air from coolant system you could be vapor locked and overheating. If the condenser temp is so hot it cannot reject heat from refrigerant the system may shut down on high pressure.

Don't know what year or make of van, but, just out of curiosity, when you turn the heater on when the temp gauge is pegged, do you have really good heat out of the vents? If not, there is air in the engine cooling system/no flow type deal going on.

If the scanned sensor reading matches the actual condition, look for basic causes of the condition.

In this case, the scanner indicates a hot engine and engine is running hot.

It means you need to check for a cooling system related fault.

Without knowing what year/make/model/engine combination you have, I would look for a thermostat related issue first, followed by checking for trapped air in the cooling system, followed by inadequate circulation due to a faulty water pump or clogged radiator.

If those items check out, less likely candidates might be looked into like combustion gas in the cooling system (head gasket).

So... a thermostat change and complete coolant flush and refill is not a bad idea, even if not the issue? Relatively cheap and easy and I don’t know when the coolant was ever flushed out.

Cone to think of it and now that you mention it, yesterday when it started warming up past normal the heater wasn’t blowing hot. Warm, but not hot. That was after I added some water so I likely did create an air bubble. So perhaps I should just wait and give it a few days worth of driving and see if the level in the overflow drops, indicating the air has been burped out?

Or should I proceed with the thermostat and flush?

quote:

heater wasn’t blowing hot.

Blocked heater core is a possibility. Does it run normal temps while at speed and start heating up at stop lights. Does opposite happen with how the heat works? Ok while still, colder while moving? If yes, get car warm, feel hoses going in and out of heater core and see if they are same temperature. If they are the same temp then coolant is flowing.

Not all vehicles are the same, some have pressurized over flow tanks, some are vented to atmosphere. Most vehicles can run with the pressure cap off up to normal operating temp.
Meaning that, with the engine cold, remove the pressure cap on the system and start it, it will push some out at first and make a mess, but then will drop out of sight, fill it up and reinstall the pressure cap.
Edit to add:
I searched your previous posts to see that your wife has a 2004 Sienna that had a cold misfire, is this the same van that is overheating now?
There is a large oversized funnel that locks on the coolant filler neck for doing this.
Many of the newer coolant systems require this to get the air out.

This message has been edited. Last edited by: rizzle,

quote:

Originally posted by Skins2881:

quote:

heater wasn’t blowing hot.

Blocked heater core is a possibility. Does it run normal temps while at speed and start heating up at stop lights. Does opposite happen with how the heat works? Ok while still, colder while moving? If yes, get car warm, feel hoses going in and out of heater core and see if they are same temperature. If they are the same temp then coolant is flowing.

Heater hadn’t been used in months until it overheated the other day while I was going to attempt to add R-134a. It overheated then while I was waiting for the compressor to kick on, which it wouldn’t do that night. Full boil over. I ran the heater and it was hot while it was redlined.

The next day I changed the ECT and added more than half a gallon of coolant, which I’m assuming was lost on the boil over.

The van was driven some the following day, but not much. It still showed the same symptoms, but not to the same extreme level. Meaning, I’d notice the AC stop blowing cold and the engine temp rise a bit, but not to the same level. While the temp was approaching redline I turned it to heater, only mildly warm.

So tonight in opened the cap back up and it finished off the gallon. I ran it at idle then for over 30 minutes. It never went above 200 (yesterday it hovered around 212 or so) and the AC seemed to cycle on and off normally and remained cold. This whole time it was idling I was getting bubbles coming up to the radiator cap. There was still a trickle of bubbles coming up when I buttoned it back up due to time constraints.

So I think the ECT was intermitently acting up which resulted in that boil over which resulted in it running warm yesterday still.

I think this issue might be solved.

quote:

Originally posted by rizzle:
Not all vehicles are the same, some have pressurized over flow tanks, some are vented to atmosphere. Most vehicles can run with the pressure cap off up to normal operating temp.
Meaning that, with the engine cold, remove the pressure cap on the system and start it, it will push some out at first and make a mess, but then will drop out of sight, fill it up and reinstall the pressure cap.
Edit to add:
I searched your previous posts to see that your wife has a 2004 Sienna that had a cold misfire, is this the same van that is overheating now?
There is a large oversized funnel that locks on the coolant filler neck for doing this.
Many of the newer coolant systems require this to get the air out.

Yes, same van. Hopefully the issues aren’t related. There was no sign of coolant in the cylinders when the plugs were changed or leakdown performed.

As I mentioned above, lots of bubbles were coming out tonight as I idled the engine with the pressure cap off. Hopefully this problem is solved with the escaping air. I think it’s mostly out, there was just an occasional burst of small bubbles surfacing.

I hate to say it, but a lot of bubbles coming out of the radiator while it is idling with the cap off generally indicates a blown head gasket and coolant temps over 220F generally insure you blow a head gasket most of the time. Keep an eye on it, but you may be doing a coolant pressure test, then a leak down test next. (A bad thermostat could also cause an overheat sitation like this also).

quote:

Originally posted by jimmy123x:
I hate to say it, but a lot of bubbles coming out of the radiator while it is idling with the cap off generally indicates a blown head gasket and coolant temps over 220F generally insure you blow a head gasket most of the time. Keep an eye on it, but you may be doing a coolant pressure test, then a leak down test next. (A bad thermostat could also cause an overheat sitation like this also).

I had that nagging thought in the back of my head too. There was no sign of coolant in the cylinders during the leak down or the plug change.

But that was before the overheating the other day. I’m going to watch it over the next few days. I think I’ll wait on the thermostat for now and just see how it behaves. If I can get a year out of it without major issues I’ll be happy, kinda.

If a head gasket lost integrity would there now be white smoke coming through the exhaust?

ECT will not cause an overheat, it is a sensor. The erroneous readings you were getting were more than likely from low coolant. You said the fans were on the entire time, right? There are usually two sensors for coolant, one to kick on the fans at a predetermined temperature. The other the ECM monitors for emissions. Now the fans could have been on simply because the A/C was on. Don’t know unless I see it for myself.

The overheat is being caused by a lack of coolant and/or flow. The question is what is causing the low or no flow coolant. A stuck closed thermostat will definitely cause this, but it will overheat every time the engine is run for a time.

When the engine overheated, was there a lot of coolant visible under the hood from the overflow tank? Half a gallon is quite a lot of fluid.

Does the engine still have a misfire? If so, and there is a lack of copious amounts of coolant leaking from the engine bay, the engine might be consuming it via blown head gasket. Now the inverse can be true, a blown head gasket can pressurize the cooling system and push coolant out causing an overheat. This all depends on where the break is on the head gasket, or if the head is cracked.

Right now I would check the oil for contamination. Run the engine for a couple of minutes then check oil for milky color. Next, I would have the cooling system checked for exhaust contamination. This will tell you if you have a blown head gasket that is blowing into the cooling system.

If these check out, the least I would do is make sure the cooling system is properly purged of air. A thermostat change would not hurt either. Before throwing parts at it though, a proper diagnosis is in order.

If you re-read your original post, it all fits together, the A/C trouble after the leak down test (which made the small head gasket leak larger). It was originally noted that the CAT will burn off any white smoke from a small leak.
Now the leak is getting worse and has started pumping compression air into the cooling system.
I suspect the massive leak down in #3 was not past the rings or valves, it was going into the cooling system.

Thanks for the input gents, even if it isn’t encouraging.

The misfire code is still getting triggered and is occasionally noticeable at start-up.

I’ll check the oil for “milkyness” on the dipstick and track down a coolant gas tester.