How cool is too cool?

[Lightyear]

A few weeks ago I started to get the SES light and a lower-than-normal reading on the coolant temp. My FLAP store pulled the code with an Actron, 'coolant temp too low'. I replaced the sensor in the crossover with a new Delco, all was well. For a bit. Got the light again after startup and about 1 mile's worth of driving on a 34 degree morning. Plugged in the block heater while the Burb was in the garage this morning. The SES went out after startup, but the temp gauge still reads lower than it used to. Is this related to our chilly North Georgia temps, or are T-stats and a fan clutch in my future?

Thanks, as always, for your help gang!

[JohnC]

Unlikely the fan clutch has anything to do with it. I'd change the thermostat(s) first; at least eyeball them to see if one is obviously stuck open.

[Hubert]

Yep more than likely the stat(s) stuck open. I think the minimum coolant temp before SES is 160F. It has to hit this within a certain amount of time or the code will set. An idling truck in cold weather won't set the code so not sure when and how the pcm counts the time limit. I think its something like within 10 minutes of driving ???? I had this code set and changed stats and fixed the problem.

[Lightyear]

Thanks for the input...both T-stats are getting R-and-R'd on Monday. This chilly Georgia weather ain't helping. I'll report back with results. Thanks again!

[agidius]

is too cool bad??

my temp needle only moves above 160 when towing, or idling in august with the A/C on.

[Hubert]

The dash guage and the PCM use different sensors. Minimum stat usually recommended is 180F. Many like the 195F too. Diesels like to be good and warm. But its a long story with the 6.5 for stat temp, electronics, and overheating there are several threads on it.

The PCM has to see 170F to re-adjust timing or something like that. 165 ish F will run ok (but with lower effeciency) I suspect with no SES.

[agidius]

I have never done any real work on this truck, and have had it about a year.
maybe I will replace the thermostat(s) just for fun.
actually, I suppose it is possible there isnt a thermostat in there.
I need to put my autotap on it to see the PCM temp reading.

this thing is currently my daily driver, and I will currently do anything for efficiency (except not drive the truck).
12 city 17 highway is something I try not to think about.

[JohnC]

is too cool bad??

You'll get better efficiency at 195 than at 160.


my temp needle only moves above 160 when towing, or idling in august with the A/C on.

The gauge could very well be off. They're really not that accurate.

[Lightyear]

Finally got the thermostats replaced yesterday. Big difference...it runs like it did before. Temp climbs up to its old operating range within 5 miles/10 minutes or so. It felt a little better merging into 65MPH traffic, too; a little more snap in the acceleration. thanks, all, for the tips...the Page proves its worth again.

[stezloco]

not having touched my 'stat(s) either , i'm guessing they're/its the car type without the bypass disc on the bottom (double acting type like you'd find in a direct injection truck normally) or you'd have overheated fast without a bypass stat in at all, as the water would short cycle through the bypass ports and not push round the radiator...so they must be the standard 'car' type...if you get my meaning..........was it missing or stuck open??

to agidius, just a little(!) note, cos i'm always interested what mpg others are getting from these old trucks...after converting your figures to imperial gallons...youre getting what i'm getting mate......skinter... he he:D... i'm getting around 9.5/13.7 at last look.
i think in the end, it'll be the overriding factor which decides whether i keep it or not. ive looked at a few topics on here, some really great info...still trying to better the mpg's ...one thing i noticed but cant as yet prove...does losing vacuum to the turbo actuator and letting it stay pushed open by the exh flow whilst driving on the motorway (highway)prevent the f.i.p from delivering more fuel because it doesnt see boost? i'd hoped somebody might have stepped in on that one...when i drove this truck back home after buying it , i didnt check the mpg but got reasonably good mileage for what i put in it..in hindsight i wish i'd checked it at the time..i'll have to experiment with that when ive got some spare time ...i also thought if i lose the vac pump/actuator and heavy steel fan and switch to 2 pairs of electric fans and a pressure actuator as well as a higher output water pump....might get me 1 mpg ......then extrapolate the savings over my mileage/remainder of life.....hey...i may just get my money back on those mods..... at the very least i can have a laugh at my own expense.......youre not alone with the fuel issue.......keep buying that lottery ticket...:D

[Lightyear]

Both my thermostats were there, and both looked the same. I don't know what might have been wrong with either one. But the symptoms of lenghty warm-up and low gauge readings, combined with inputs from some of the 'old heads' here made me think at least one was sticking open. Two new stats later, rapid warm-up and steady 190-195 on the temp gauge. I'll know if efficency has improved after filling up today.