Incredibly stupid question (engine temperature related) - Fuel Economy, Hypermiling, EcoModding News and Forum

Burnt · 12-08-2009, 07:35 PM

I'm not a mechanic, or mechanically inclined

that being said, my '09 cobalt doesn't have a temperature guage...instead one of the readout options is the temperature of the coolant....

is that close to what the actual engine temperature is? and if so, what are acceptable temp ranges? I'm planning on putting in a stealth grill block, and obviously I want to keep an eye on the engine temp during the whole process

I'm not so much worried about it now (ohio winters are heinous), but more so in the warmer summer months

thatguitarguy · 12-08-2009, 07:41 PM

Temp gauges read coolant temp, so that is what you want to watch.

Welcome, and good luck!

MetroMPG · 12-08-2009, 07:46 PM

You could do a simple test: next time you get to your destination, let the engine idle (heater off) and watch the gauge slowly climb.

Listen closely - after some minutes, the electric radiator fan will kick on. Note the temperature when it does (likely somewhere north of 200 F). The number you see on your read out is what you want to know.

You should size your partial grille block so your fan isn't coming on any more than normal.

And if you change your typical driving pattern (ie. road trip in the hills/mountains) remember the block may not be right for the load / heat generated. Don't melt your engine.

bgd73 · 12-08-2009, 07:47 PM

coolant is up top, don't forget the oil temps in grill blocking.

approaching 260 F is very bad news...you could even maintain a good thermostat reading and blow out the bearings in the other world of the engine, the oil..

thatguitarguy · 12-08-2009, 08:17 PM

I guess it depends on if you have an oil cooler or not. All my cars have only the oil pan hanging in the breeze to cool the oil. The rest of the cooling needs for the engine are handled by the coolant flowing to the radiator. And the transmission is also cooled by the radiator, and I don't have a gauge for trans temp.

cfg83 · 12-08-2009, 08:27 PM

Burnt -

(this is a late post, others have already said as much ...)

That's a good question. The coolant temp is not the temp of the engine block, but it reflects how hot the engine block is.

On my car, and others from what I have read, a coolant temp of 250 degrees F is where the engine damage starts. My coolant normally runs around 190 degrees F. When I am stuck in traffic it can heat up to 220 degrees F. At that temperature, the ECU/PCM turns the electric fan on. It keeps the fan on until the temp falls to 210 degrees F, and the cycle repeats itself as long as I am stuck in traffic.

I am sure your Cobalt does something similar. You can find out by :

1 - Idle your Cobalt in the parking lot
2 - Watch the coolant gauge slowly rise
3 - At some point, you will hear the electric fan come on.

Note where the needle is on the coolant gauge. That *should* be around 220 degrees F. If you had a Scangauge, you would be able to tell the exact temperature when the electric fan turns on. I am guessing you could also find out this temperature on a Cobalt forum.

Don't do this test with the AC on, because that *should* turn on the electric fan by default. Maybe not, but that's what it does on my car.

On my car, as an additional precaution, I have a manual fan radiator switch. I can use this switch to turn on the electric fan when I don't like the coolant temp. I am more conservative than the ECU/PCM. I usually turn the fan on at 210 degrees F and turn it off at 190+ degrees F or when the car is moving again.

CarloSW2

jamesqf · 12-08-2009, 11:01 PM

Quote:

Originally Posted by Burnt

that being said, my '09 cobalt doesn't have a temperature guage...instead one of the readout options is the temperature of the coolant...

Could you elaborate on what this readout is? Is it something like a ScanGauge, giving you an actual temperature value? If so, it's probably pretty accurate. Temperature gauges, OTOH, I've never found to be more than ballpark accurate, if that.

For what temperature to run at... Well, I'm not familiar with the Cobalt at all, but on the Insight (the only car I have that's new enough for a ScanGauge to work) normal operating temperature is the 195 F thermostat opening, and on fairly flat roads and outside temps below 100 or so, it seldom goes more than a degree or two above that. It takes a mountain climb - say 4000 ft of 6% grade - to get it up to 210 F, and given that the top of the climb is about 9000 ft, I don't like to see it go over that. I've never seen it hit 220 F. If it did, I would stop and let the engine cool.

Maybe I'm overly conservative, but that's my $0.02 worth.

Thymeclock · 12-08-2009, 11:31 PM

212 degrees is the boiling point (unless you are at high altitudes, which is even lower). Even with radiator coolant, it's best to keep it below that temperature.

Personally, I wouldn't attempt a radiator/grill block without a temp gauge (nor would I own a car that didn't have a temp gauge.) The idiot light comes on only after the car is overheated. IMHO, that's too little, too late.

I notice he said there is a coolant temp readout. He could work with that. Much better than idiot lights or gauges that have no markings on them (which are still better than nothing).

thatguitarguy · 12-09-2009, 12:56 AM

212F is the boiling point of water at sea level, but with a 50/50 coolant mix in a pressurized engine cooling system, the boiling point is much higher, even at high altitude.

The only 3 gauges my 95 Metro has are speedo, fuel, and temp, so I would doubt that any car made since then would have at least a relative temp gauge.

He did say one of his readings was coolant temp, so I think he should be fine to experiment with a block, if he monitors that temp.

thatguitarguy · 12-09-2009, 01:05 AM

Quote:

Originally Posted by Burnt

I'm planning on putting in a stealth grill block, and obviously I want to keep an eye on the engine temp during the whole process

One thing I would suggest about a "stealth" block, is that you be careful about the placement. Keep in mind that the idea is to force the airflow up and over the car. It's not to keep air from getting to the radiator, although that is generally what is going to happen to some extent. So keep the block as close to the grill as possible, and away from the front of the radiator as much as possible, so that even though you are blocking off the airflow, at least some air will be able to get to the front of the radiator.