Nov
13th
2022
Car Mystery I'm CCing y'all on while I go and turn on the Biscuitsignal lantern · 9:11pm Nov 13th, 2022
Hey Biscuit, fellow FimFiccer Latrans and I have a sherlockian mystery we would love to hear your two cents on if you're free later this afternoon/early evening:
"The case of the 1998 CNG Honda Civic that is overheating despite the fan temporarily being wired to stay constantly on when the car is running, which it is, the coolant pump seems to be working and the coolant is full, and the engine and oil and all that seem to be in good working order."
Mouthful of a title I know; I'm still workshopping it.
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Super Trampoline · 126 views
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#Car
#mechanic
#fixing
#crowdsearching
#suggestions
#help
#overheating
Now I see there's a blog post . . .
Well, gonna just copy-past the PM response so everyone can enjoy it
The four most likely culprits are these:
1. If it has an AC condenser in front of the radiator, the cooling fins could be clogged with dirt or debris, which would mean it can't cool efficiently. This is also possible if it's just a radiator, but it's less likely and a lot easier to spot.
2. The thermostat could be stuck shut. If it is, when the engine heats up, very little coolant will flow through the radiator.
3. The coolant pump might be turning, but are the impeller blades that move the coolant? Are they even still there? Metal ones sometimes rust off, and the plastic ones sometimes break off, or the impeller--which is press-fit on the shaft--might be loose on the shaft. This can be difficult to diagnose, since you can't see it unless you remove the water pump.
4. Coolant passages, most likely in the radiator, could be plugged with sludge or rust.
Depending on where the car is operated and what its maintenance history is would change which is the most likely. Cleaning between the condenser and radiator (if the condenser is in front of the radiator) is easy enough to do, and the thermostat might be cheap and easy to change. If the coolant hasn't been maintained, sludge or rust in the radiator is a possible cause, which will most likely mean the radiator needs to be replaced (they can be cleaned out, but it's usually cheaper and faster to just replace them).
When the engine is COLD--when the car has sat for many hours to cool down--you can take off the radiator cap and see what's in the radiator. If it's got a conventional overflow bottle, it's possible that the bottle could be full but the radiator isn't.
--admiral biscuit
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5697741
Turns out #4 was the culprit. The car has a new radiator fan temperature switch, coolant temperature sensor, thermostat, and water pump. I neglected to properly inspect the inside of the radiator and missed the rust/sludge build up. A previous owner apparently used water instead of coolant for an extended period of time.
Fortunately the radiator is pretty easy to pull (one bolt, two coolant hoses, two transmission fluid hoses) so it was a fairly minor operation to get it out and backflush it. Pulled the thermostat and flushed the motor too. My recommendation for the long term is to replace the radiator but it's staying cool(ish) for now.
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Reason #1 why I'm a digital mechanic instead of an auto mechanic. I was going to guess the thermostat, because way back in the cave man era of cars, I had an 1980 or so Subaru the had started to run hot. The dealership sold me two different thermostats (which for the Subaru, you could install with one wrench and a screwdriver in two minutes) One of them had the car running dangerous-hot, the other kinda-sorta-dangerous hot. So I took the thermostat out and ran it that way for a couple of weeks until I could get time to flush-fill-flush-fill-flush-finish the thing (it spat out dirty water with two of the flushes, third was finally clean as a deacon after a colonoscopy). Then the regular thermostat worked fine. Go fig. You put 200k miles on a car and it gets all demandy for things.
(Subarus of that era were very anti-delicate. Fuji Heavy Industries made solid parts. You could take the whole engine apart with five wrench sizes and one socket for a couple of bolts, and the spare tire sat on top of the engine so there was lots of space in there once you put it to one side.)
5697882
Coupla thoughts about Subaru and why I like them:
They make basically one drivetrain, and they've spent years getting good at it.
Their timing belts have marks on them you line up with the marks on the pulley.
They include tools for when stuff breaks
They're the first automaker I know of to include windshield wiper defrosters
They're the first automaker I know of to include a prop for the spare tire cover (after they moved it out of the engine compartment)
They had a tool--and instructions--to crank the automatic lap belts and sunroof into position, if the motors failed.
They also include the screwdriver for the roofracks (and there are a bunch of Subarus where I personally put that tool in the vechicle)
They had the option for weather radio on their digital radios; AFAIK still nobody else does that.
5699423
Well, that's what makes a Subaru a Subaru!
5697882
You certainly have a way with words. Have you considered creative writing?
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5697793
Happy to report no more overheating issues except for about once or twice a week I accidentally put it into third gear instead of 4th gear and then it runs a bit hot and I'm like oh Motors revving pretty high well that's why it's in the wrong gear
5699423
The problem I have with Subarus is basically the same problem I have with most cars: the motor was designed and assembled outside the car, which leads to all kinds of headaches when you actually have to do any in-depth work on them. Subarus, at least the ones I've seen, are extra horrible though because, with the boxer engine, they have the heads up against the frame rails and you can't even remove the valve covers without yanking out the motor first.
5699616
That reminds me, don't forget to get a fluid and filter change on that transmission. The stuff in there has been around the block a few times. Also, how's the oil level? Staying good or are you having to add some regularly?