Is the cooling system on these 7.3s too efficient?
During the summer, I am lucky if the temp needle gets higher than about 1/3 the way up in the "normal" range. Even on 100+ degree days.
During these last few days where it was down in the single digits to below 0, the needle barely gets past the bottom line of the normal range.. maybe 1/4 the way up when driving. At idle it will eventually drop almost to the bottom of the normal range.
It will come up a bit with driving around but if I let is idle long enough, the temp starts to drop.
I do get heat in the cab...it will defrost just fine but if I let it sit long enough you can feel a little drop in the air temp. Not much tho.

Coolant is at the full mark, normal color and clean.
I am thinking that maybe the thermostat is not closing all the way so some of the coolant is just constantly flowing. I did replace the water pump last summer but kept the same thermostat.
Truck is an E99 with about 296K on the clock. Almost all stock...no mods that would affect the cooling system.

Thoughts?

Thanks all!

Your thoughts?

 

IMHO: 7.3's have a very efficient cooling system.

Perhaps something that affects the longevity of the engine when maintained properly. Possibly that's why we still see so many and most achieve 250k+ without catastrophic failure. No plastics like the newer ones and no EPA Self Destruction Requirements

My 99 with 250k still cools just as it did when I picked her up. I use a 203* thermostat and rarely see 195* on a hot day unless towing a load.

I've seen it 210* under a 15k lb. load crossing the Appellations in August when it was 100*; but that's it. They do have a substantial by-pass built in the system which prevents them from reaching Op Temps. Keeping the fins clean (along with the TC and CAC) are just as important for maximum air flow. I've never seen more than a 20* difference in OT & ECT.

I still run the Green, flush and change the thermostat, o-ring, and T-Stat housing every 15k miles. Keep the SCA at recommended levels (test quarterly) and have replaced the Water Pump only once.

Maybe I just got lucky - It's a Texas Built 99.5.

 

As for the gauges, I use the Scan Gage-II (x2) and monitor what the PCM is seeing. The Cluster system is approximate and often is a poor indication of activity. I've seen 6.0 Boil Over and the gauge was in the middle - Maybe just a thing with that truck.

 

I guess it depends on what you mean by 'too efficient'. The cooling system is way more than an unloaded truck needs. It was designed to exchange heat up to about 23k lbs gross however in my experience it seems to work pretty well up to 25k-26k lbs with the 3.73 gears. Maybe 3k-5k more if you go with the 4.30 or 4.88 gears.

About 1/3 up the Normal range is about where most of these sit. However, the actual coolant temp can swing from 190-230 degrees and that needle in the dash won't budge. it takes about 235-240 degrees to get that needle to move to the upper end of the Normal range. 250-260 degrees will put it in the red and illuminated the "Check Gauges" light.

If you install a coolant temperature gauge then you can see what the real temps are. Alternatively, you can connect a scan gauge or tool and monitor engine oil temp and that can help you determine if your t-stat is stuck open. Not sure how cold it is where you live but I can easily get my oil temp over 200 degrees even when it's 50 degrees out under normal driving. If you pull over and let the truck idle and the engine oil temps falls below 180 then you might have a stuck t-stat. It's happened to me once...my oil temp was falling down to 160 once I pulled off the highway so I knew something was up. A new t-stat solved my problem.

I presume you are aware the PCM only monitors the engine coolant temp sensor on manual transmission trucks. Automatic trucks do not read actual engine coolant temp...the value given is a calculation and may not reflect the actual temp of the coolant.

 

Interesting observation. Yesterday, when my CPS starting cutting out in the Philly airport parking lot in 28° weather, I hooked up AE after I replaced the CPS, and I decided to look at the coolant temp (for the first time ever) as it warmed up. I was curious to see the relationship between the gauge and the numbers on AE. Once warmed up, my gauge was where it always sat, but AE reported 300°F! It's an early 99, and apparently there are a few things that my PCM program doesn't do (like PERDELs, vehicle speed). Was wondering if the coolant temp was also incorrect for this reason.