It’s a 2002 Chevy Astro. I don’t know if these two problems are related.
About 3 years ago, I was sitting stopped in traffic when the temperature gauge suddenly spiked to overheated. I turned the heater to full blast and moved into flowing traffic, which brought things down to normal. Took it to the mechanic who said that there was something wrong with the coolant system and it would take $1500 to fix. Since I didn’t have that kind of cash, I decided to see how things went. Never happened again.
Until 2 weeks ago. The heater stopped working entirely and the temperature gauge will randomly spike to overheating. The spikes never happen when I’m moving down the freeway, but they come on so rapidly that I’m not sure I believe my temp gauge. I mean, I’ll come down and off-ramp and be waiting at the bottom for all of 30 seconds and the temp will go as high as the dial reads. Then, I’ll start moving again and it will come down again just as quickly. And the spikes are not reproducible. I’ll go a few days of normal stop and go traffic with nothing, just to have it spike repeatedly in one day with no change in driving behavior. The weather hasn’t been over 55 degrees here in weeks. Is it possible for an engine to heat and cool down that quickly? Is it related to the heater not working?
The heater not working suggests there’s a large pocket of air in the cooling system. If so, it’s because coolant has leaked out. You may be right on the cusp of severe overheating and resultant expensive damage.
Check the coolant level in the radiator. DEAD COLD ENGINE ONLY remove the radiator cap to do this. The level in the overflow jar is NOT a reliable indicator of whether or not the system is full. Top up as needed; if it was low get the leak found and fixed as soon as you reasonably can.
Will do, although we just had the oil changed and all the fluid levels checked a couple months ago and everything was nominal (there is a slow leak in the oil lines that we know about).
What am I looking for when I uncork the radiator? How cold is dead cold? After sitting overnight only, or is a few hours of sitting ok? Changes whether I can check this now or have to wait for tomorrow.
I had a Olds Cutlass in which the onboard computer decided to wig out. It would operate normally for a while, then the fan would go off. Then on. Off. On.
You’re looking to see it filled pretty much right up to the top. If it’s not refill it with a 50/50 mix of antifreeze and water (unless it’s premixed) right up to the top. As for dead cold, Gary can answer better then I, but I would say an hour or so. Also, to be on the safe side if it hasn’t been more then a few hours since you are sure it hasn’t been run, put a thick rag of the radiator cap when you unscrew it so your hand doesn’t get burned if it spews a bunch of steam out.
Also, I’m not a mechanic, but low coolant was my guess as well. Overheating engine plus no heat in the cabin points to that.
A lot can happen in a couple of months.
Overnight is perfect, several hours is probably fine. If you can hold you hand on the top of the radiator it is cool enough to check. If you can’t leave your hand there, let it cool a bit longer. Boiling hot water sprayed all over the front of you is not fun, take that from me (been there, done that)
If the engine was cold when this was done, the level in the radiator should have been checked. But if it was a while-you-wait service, the radiator cap would not have been removed because a) a bunch of hot coolant could have spewed out, making it low on coolant even if it wasn’t before, and b) the guy doing the oil change likes his skin unburnt just like the rest of us. They would have checked the overflow jar, with no real knowledge of whether the engine and radiator were full or not.
And as Rick suggested, even if it were full at that time, that doesn’t preclude a leak from developing and a bunch of coolant being lost in the meantime.
Ok, attempted to get the radiator cap of to no success. Neither the husband nor I could figure out how to get it free without a hacksaw. But, the overflow container for the coolant was very low. Topped it off with premixed antifreeze. Seems to have done the trick as the cabin heater now works. No evidence of temperature gauge spiking so far. Will try to get the van in for coolant leak checks as soon as possible.
Could someone explain how a lack of coolant leads to no heater?
Push down…hard and twist to the left about a quarter of a turn, then stop pushing down so hard and unscrew it the rest of the way. The idea behind this is that after that first quarter turn it can let out the pressure before you unscrew it the rest of the way.
The heater core is up higher compared to the rest of the system (you should see two hoses that come from somewhere around the engine and travel up to a box mounted on the firewall usually on the passenger side). If the coolant is low and there is air in the system the air will rise to the top, where the heater core is and coolant won’t circulate up there very well. At least that’s my understanding of it.
Hmm, that sounds suspiciously similar to what we were trying with the radiator cap. Will try it again later.
So, if the coolant doesn’t circulate up to the heater, it won’t work at all? I always figured it was just a hot wire with a fan, like a space heater for your house. No coolant needed. In fact, I was told that if the car is overheating due to stopped traffic, you were supposed to put your heater on full blast with the intention of adding extra flow-through over the engine while you move the car either to a place to stop or to faster moving traffic. Am I on crack?
Nope, the heater is just a small radiator right behind your dashboard. Working on the same coolant that cools your engine. The reason behind putting your heater on when stopped in traffic (or to help an over heating car) is because you have another radiator siphoning heat out of the engine. Actually, what you said is correct you just ever so slightly mis-understood or mis-heard. When you said " full blast with the intention of adding extra flow-through over the engine" that’s correct, but it’s not air, it coolant, and it’s not “flow-through over the engine” it’s just “flow through the engine” as in extra coolant flowing through the engine.
Wrong on both counts. It gets its heat from hot liquid (engine coolant) flowing through it, the fan moves air that takes the heat from the heater into the cab.
Could be.
You put the heater on full blast to maximize how much heat you remove from the heater = remove from the coolant = remove from the engine.
