2003 6.0 Thermostat stuck open?
 

Hey All,

Lately I've been driving my truck back and forth between the SF bay and San Diego traversing through the I-5 valley in 95-100 degree weather.

In the SF bay 75 degree weather, my ECT/EOT temps are usually 186/194 @ 65-70mph.

In the valley heat, lately I have been seeing 188/215, 190/218, 194/219 all at about 75-80mph and when going up the grapevine I saw 210-215/228 to 230 going up at about 65mph. This is all with about 350lbs of stuff in the bed.

When I get to San Diego it's about 10-15 degrees cooler and the temps are 186/196, 190/202.

Is my thermostat stuck open? I don't remember having this much of a delta previous years ago but I never recorded the information. I'm not too worried about it right now since the EOT always drops after climbing a grade.

Also, from time to time just driving around running errands, it will throw a P0404 code and at random times it will throw a P2287 code and romp a little bit at idle. Any ideas on these two error codes please?

You need to get your spread doing 60 to 65 on flat level ground after the engine is totally heat saturated. App. 20 miles of highway driving at 60 to 65.

Well that doesn't make sense. I thought the 15 degree delta rule was/is applicable in any load/unloaded condition?! Plus how do I check to make sure the thermostat is opening and/or closing? Shouldn't the temp climb and then lower as the thermostat opens? Will the thermostat open at 186 degrees?

At 65mph on flat land my spread is 186/194 all day 20-100 miles.

If your coolant temp is stable at 186 - 190 your thermostat is opening at around that temp. If it wasn't opening your temp would keep climbing until the engine shut down. If your temps are in the 160 - 180 range it's stuck open. That's for normal flat unloaded driving. Loaded, big hills, higher speeds and up to 215-220 is normal for a short spike followed by the fan coming up to speed and the temp dropping as soon as the higher demand drops away. Your EOT coming down nicely when the load is off is a very good sign. If you want to tell if the thermostat is opening just put your hand on the radiator inlet where the hose from the thermostat runs to. If your hand hurts, the thermostat is open... :)

P0404 is often a stuck or failed EGR valve, and P2287 is intermittant ICP which could cause a romp at idle.

Brian

Thanks Brian. Do the 17-18 degree deltas give you cause for concern even though the EOT temps drop?

I'll be replacing the EGR valve hopefully sometime this week. Is there a good fix for the ICP?

The temperature difference doesn't worry me because I don't know the conditions when they happened. The only time the temperature difference counts is under the standard test condition - normal ambient temps of around 75 degrees, no load, 60 - 65 mph, flat. Anything else the test doesn't count. Some things always count, regardless of any other test. One is does oil temp start to come down within 3 - 5 minutes of removing a big load - coming off the highway when towing, cresting a big steep hill, dropping speed from 85 mph to 60 mph. That says the oil cooler is working. Another thing that always counts is coolant temp. 190 is ideal, 185 - 195 under moderate load and 75 - 85 degree ambient temp is normal, up to 220 under a big load, fan comes on around 215 usually, and coolant pulling down quickly when the load goes away and the fan is on.

I recently towed around 8K for 3,000 km with a stuck turbo so I was pretty down on power. My coolant ran between 188 and 220, and my oil temp ran around 200 to 225. I "usually" had a difference of around 6 - 10 degrees but I regularly had a difference of zero degrees - cresting a hill, coolant temp spiked to 215 and oil temp was 215 for an example. 2 minutes later coolant was 190 and oil temp was 212. Did I have a difference of zero, twenty two, or eleven?

I hope this helps.

Brian

Ok thanks Brian. That puts my mind at ease a bit. I do have a few questions when towing properly with these 6.0s.

When I was towing my 7000lb boat/trailer down to San Diego, I had to traverse a 7% grade for at least 15 miles. Upon initial climb I was doing 65mph. I was watching my temps very closely and i'm not one to punch the throttle hard I saw the ECT climb to 225-228 degrees and the EOT climbed to 241-243 degrees. By that time I had reduced my speed to 45mph and then a big rig had pulled into my lane and slowed me down to 25-30mph. ECT sustained 228 and EOT peaked to 245. Not once did I decide to punch the throttle given the already semi high temps.

Question is, does slow and steady win the race or could I have pushed the throttle a little bit to gain speed again?

I gotta tell ya, sometimes I feel like I baby the crap out of my truck because of this Edge Evolution gauge/meter. Had I never done any research about any of this, i'd have punched the throttle and used all the power that engine has to offer without any reservation of those temps. If I fully bulletproof this motor, can I run it like a raped ape?

Please advise, should I continue to go slow and steady or can I actually use the power in reserve regardless of those already semi high temps. The research I have done so far is that 253 degrees EOT are pretty dangerous.

Thanks in advance.

Erik

When towing a grade if I start getting uncomfortable with the coolant temps I'll slow down to 50 to 55, pull the gear shift manually down in to third and set the cruise. Temps usually drop dramatically. You are doing what the gearing is there for instead of over working the engine. This is also while in tow haul mode.

I'd have done what you did, get up the hill and then carry on. A tip - if the factory temp gauge starts to show hot, THEN you are getting hot. Until then, it's in the range of normal. We tend to ignore the factory gauges, but they are actually pretty good at telling you when there actually is an issue.

Brian

JMHO but when the factory gauge says your in trouble it may be too late. That's why I have the Scangauge. I like numbers. not generalities.

I too like to know before an issue has become a problem, but you know that when the factory gauge starts telling you to pull over you should pull over now...

Brian