15* Delta T - Ford Powerstroke Diesel Forum
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Old 01-03-2012, 04:34 PM
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15* Delta T

Ok I thought I had it figured out, my truck will see 15* Delta T EOT vs. ECT after cruising at 65+ for 20 minutes or so. I read the TSB (which I've been trying to find again and can't find it) and it said something about checking this while under load then I read something about seeing higher than 15* while cruising and this was normal. Ok, so what should I be concerned about???? Coach.
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Old 01-03-2012, 04:55 PM
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With a 15 degree difference at highway speed (55-65mph) after the engine is warmed up (no longer climbing steadily and ECT has reached the thermostat opening threshold at 192F) you are "under load."

Your oil cooler is most likely plugged.

You should be concerned now that coolant flow is reduced downstream at the EGR cooler where hot exhaust gases are cooled before reintroduction to the intake manifold. These hot gases may flash boil the coolant and the brazed cooling elements could rupture allowing the coolant (albeit a smaller amount than full flow) to enter the intake manifold where during the combustion process it is converted to steam. This steam is capable of stretching the torque to yield bolts and in fact hardened studs as well as warping the cast iron heads.

If you however ascribe to the logic that "under load" means heavy acceleration or towing then your current 15 degree delta not "under load" will be magnified as a greater demand for fuel in the combustion chamber will certainly produce more waste heat requiring greater thermal capacity of the coolant while the additional friction of the pistons at a greater cyclic rate simultaneously raises the oil temperature. The thermostat will be fully open at 219F and any additional heat transfer will require the full speed application of the engine fan.

The 25 degree delta was reduced to 15 degrees to allow for time to replace components before a system failure. In either "under load" by highway speed operation or heavy acceleration/towing applications the notice for action on your part is now indicated. Better to invest in a thorough flush and cooler rebuild than the same plus replacement of a failed EGR cooler and possible head gasket failure precipitated by either headbolt/stud/head failures.

It's not good news but it is preferrable I think to common reports of plumes of white smoke and lost power.

Good luck.

Jonathan
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Old 01-03-2012, 04:55 PM
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maybe your referring to coolant system psi...your oil cooler is clogged, i think 10* was max, after that you would have to replace your oil cooler, cooling system flush, prior to swapping oil oil coolers.
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Old 01-03-2012, 05:02 PM
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The typical coolant system pressure is ordinarily below 16psi.
The indirect measurement for insufficient coolant flow through the oil cooler is an indicated temperature difference of 15 degrees between coolant and oil as measured from the stock sending units when the vehicle is at operational temperature and under load typically as driven on the highway at between 55 and 65mph.

There are instances where the "rule of thumb" (15 degree difference) is not always accurate or precise. When the ambient air temperature is very low, coolant heat transfer is very fast and there may be higher than "ordinary" temperature differences than from temperate weather conditions. Saying that, 15 degree differences ought to be closely monitored and preparations for oil cooler rebuild following a thorough cooling system preparation conducted.

Jonathan
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Old 01-03-2012, 06:28 PM
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Thanks for the replies guys, Col. thanks for your service, my dad was a Lt. Col USAF, he passed away a few years ago, I was Navy E6 GSE1 (SW). Anyway I didn't mention that I don't have the Gold coolant, it's been gone a long time. I am planning on doing the oil cooler and egr delete pretty soon, waiting on tax return. Coach
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Old 01-03-2012, 06:39 PM
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Let me say "Thank you" to you as well, Coach. Your service as well as your father's gave me the opportunity to continue to serve. It takes all of us together.

I do think you need a flush regardless of the coolant you currently have in the truck or what coolant you intend to use in the future. The blockage indicates debris in the system that needs to be removed to avoid the same condition in the new oil cooler. I encourage folks to get the coolant analyzed too for traces of solder bloom and other metals in addition to regular testing of coolant pH, nitrite/carboxylate/molybdate (the principal coolant additive packages associated with your particular coolant type anyway), and freeze point.

Good luck - I think we are all looking forward to a tax return (fingers crossed!).

Jonathan
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Old 01-03-2012, 07:39 PM
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If I could ask a question.

I routinely have a hard time getting up to operating temperature. Normally I'm in the 184-188 ECT range with ambient temperature ranging from 40-65 this time of year.

The delta may get as high as 15-16* during this temperature range. When I do get the coolant temps. up to 190 and above say 192, 194, etc. the delta then reduces to 6-9*.

Presumably the thermostat is opening and reducing the oil cooler temps if I'm understanding it correctly.

So with this in mind do I have a problem? Or does my truck simply runs cool. I have read about this phenomenon here on this forum time and time again from folks who have tried changing thermostat etc.

Thoughts?
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Old 01-04-2012, 05:42 AM
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First, I don't have the same observation for my own oil/coolant temperature differences during "warm up" to operational temperature (but my truck weighs 16,000lbs). Saying that, the difference during the run up is not the time to make the indirect assessment of the oil cooler's operational efficiency. Yes, with a greater heat sump volume (the coolant in both the block and the radiator) your oil cooler will have better capability to shed the heat in the oil. Your type and age of oil may have some affect on the readings. Another thing to consider is that your thermostat may be stuck open allowing the coolant to remain cooler for a longer period of time than the oil which heats up just fine. A new thermostat is about $20 and while I don't ordinarily advocate throwing parts at a problem the purchase of a "back up" thermostat isn't a very large investment. The time needed to change a thermostat is minimal, effort is small too. You may easily test the new (and the old) thermostat to validate proper operation (begin to open at 192F, fully open at 219F...using a Motorcraft thermostat of course - stamped 89-104C).

Measurements at any discrete time (of any pressure, temperature, etc.) have a relevance to be sure. However, in the case of assessing oil cooler efficiency - an indirect assessment at that - is best (fewer false positives) when the engine is already at operational temperature such as after about 20-minutes on the highway.

I think you are ok - maybe a "slow to close" or slightly open thermostat.

Jonathan
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