I've been searching for a while now but have not found an exact match to my problem.

So, Yesterday I was pulling a large load home (15K lbs) over flat land/small rolling hills and I experienced a coolant temp spike. And I am trying to figure out what caused it. I was traveling 65 mph about 2k rpm and 20lbs of boost, I was motioning the ECT, EOT, TFT, and Fan Speed via my scanguage and 99% of the time the ECT was in the 209-220 range, once it got up to 220 the fan would come on and the ECT would drop to 209 ish pretty quickly.

However, twice the ECT shot up from 215 ish to 240 within seconds then the dash indicator said check coolant temp then the fan came on and cooled it down to 200 within seconds, I did lose about 1/2 gal of coolant. So today I'm going to get a new degas cap (still OEM original) and continue to monitor the situation.

My EOT ECT delta has been a constant 10-13 degrees for the 3 years i've been monitoring it so i believe my oil cooler is still functions within spec and all my cold soak temps are within a degree or two for various ambient temps (20 -80) so all my sensors should be good.

Also, tonight I'm going to pull the EGR valve and check if there is any coolant in the intake, but if there is not, where should I start looking and what should I start worrying about e.g. head gaskets?

Sorry about the long post, just trying to provide as much background info as possible.

As usual FTE rocks!

Jason

 

What year is your truck? Hopefully you will have some wet soot on your EGR valve and maybe a bad EGR cooler. Lot easier and cheaper to fix than HGs. As far as the spike, possibly the plastic wheel in the water pump maybe broken? I know they are prone to giving out but a sudden spike like that leads me to believe something failed or stopped working as efficient all of a sudden but I guess pulling heavy like that definitely puts the strain on things. Sounds like the the fan is working properly though. Do you have/use any tuning while pulling heavy like that?

 

I have an early build 2006, and I am stock except for the Atlas 40 FICM tune that I done when Ed repaired my FICM two years ago.

 

I believe you want to park the nose of the truck on a decline, let the engine cool down, and then pull the EGR valve, looking for wetness or goo.

 

Luckily i did park it with the nose down last night so I will pull the EGR valve and report back when done.

 

If I remember correctly my fan kicks on at 210* and back off around 205*......220* seems awfully warm for fan activation, jmho.....possible your thermostat hung up for a second?

 

Sounds like you could also have a sticking t-stat. Cheap and easy to replace. Stick with OEM in my op.

 

My 07 fan kicks in right at 220 and quickly drives the temps down to 200-205. Doesn't sound like you have fan issues.
Lots of you tube stuff about the bad oem coolant caps. Replacing that may solve your issue, especially if you have puked coolant.
Inspecting the egr for wetness will help to confirm any egr/oil cooler issues.

 

What would cause the thermostat to "stick"?

 

Since the truck had been running at operating temps for some time during this run, you'd hardly expect that an open thermostat would close temporarily to raise temps, then open back up to allow a cool down.
Usually they go bad after shutting closed with cool down, and then, not opening back up with operating temps. I'd look elsewhere as noted.

 

Well I removed the EGR valve tonight and the intake was dry as a bone, no goo, no liquid. So as of now I am just hoping the degas cap released at a pressure lower than 16 PSI and the coolant flashed boiled and created an air/steam pocket that caused a temp spike.

If the degas cap does not fix the temp spikes, on to the next potential issue, besides HG, how do I determine if the water pump is bad without removing it, if possible?

 

I bet a new coolant cap will cure the spike in temps for you at least for the time being.
If you run a tune make sure it's safe for towing.
If that doesn't cure it, you'll need to diagnose (with a gauge) your coolant psi, the degass bottle will start to show vanishing coolant again.

This senario sounds all too familiar, there should be no surprise regarding the 6.0 dilemma of TTY head bolts causing HG seepage. Can't even rule out a cracked head. Denial is most often the first hurdle.

 

Not much chance the water pump will be an issue unless it's leaking from the front seal.
Replace the coolant cap and drive. I bet that's the issue.
If not, check out the pressure testing on you tube for help.