Gents, I'm new to this forum so thank you for the help in advance. I'm hoping to find a ford diesel mechanic that can provide some wisdom. First the story: Had my 05 6.0 rebuilt 18 months ago due to head gasket. Deleted the EGR, new heads, head studs, o-ring heads, oil cooler, fan clutch, water pump, and more parts than I can write. Ever since the rebuild the oil temp was running high; 230, 240, 260 depending on whether towing or not. ECT maybe 210 max. The mechanic replaced the oil cooler under warranty but nothing changed. Over the last weeks as I drive it here and there, pulling my boat, oil temp goes up to 260 or more. I use a scan gauge to read temps. On top of that, I will get a “ding” on my dash warning me to check the gauges. Maybe 10 seconds after, the dash water gauge will go up to the top but the scan gauge stays the same – maybe 200/210. I get out and look at the degas bottle and it has coolant and is not over flowing or spewing water out. There is no indication that its as hot as the dash gauge says. I turn the truck off and then back on and the dash gauge returns back to the middle. Go down the road a ways and “ding” again after a little while.

So, I’m not sure what to believe about coolant, ECT or oil, EOT. On ECT, the dash gauge and scan gauge do not match, at least once you hear the “ding”. The oil dash gauge shows below the middle but who knows what that means. Also, at times on the scan gauge, the ECT will flash from 245 to 210 in a second. It mostly stays low but it does switch from time to time. I put another ODBII scanner on and it shows the same as the scan gauge.

It’s possible the EOT is as high as it says but since the ECT is acting flakey, it makes me wonder about everything. I know all the recommendations about the delta between ECT and EOT but that may be a secondary issue at this stage. So, any wisdom for me?

 

Have you done a 12 hour "cold soak" to verify the sensors are accurate? They should be within a few degrees after sitting overnight. If not, that's the first thing to take care of.

 

Well, they are relatively close to the same in the morning when i start it. I'll check again in the morning to be sure. When I start driving the ECT slowly climbs and EOT lags. After a while, EOT slowly takes over and climbs above ECT. If I'm not towing the delta may be 20 to 30 depending on how I push it. If towing my boat, EOT went as high as 262.

 

Swap the sensors and see what you get. They are the same.

There is an oil cooler bypass valve that could be the culprit, but that is rare. It it says open, it could explain oil climbing because the oil is mainly bypassing the cooler. Can't replace the bypass valve without replacing the oil cooler cap/cover.

I had relative high oil temps I fought for a while, but muy ECTs were also slightly high. Changed thermostats and problem solved. My TStat was not opening enough. I had a cheap aftermarket tstat, but went with a Mishimoto and my delta never gets over 15 even when towing my 10.5k camper ( wind sail). If I tie 80 mph, the delta slightly exceeds 15.

At 65 mph, my delta is 5. I have a new oil cooler and you can drink from my coolant system it's so clean.

 

Thank you BryanStein.
Is the oil cooler bypass valve something that comes with a new oil cooler? Reason I'm asking is that I just changed the oil cooler. The new one and old one act the same.

Swapping the sensors is an idea - i didn't know they were the same. I might also get another T-stat and see if that changes the equation.

 

You hear the fan real good kicking on?

 

Jumping gauges is a sign of Bad sender or wiring issue

IF I understand the symptoms correctly
Taking a guess here but I find it unlikely you have 2 bad senders at the same time id be checking the harness


When my TFT sensor was bad it would jump all over send the truck into limp mode
when you see check gauges light up its in limp mode or atleast that how my tft was


Theres no way the truck fluid temps change 35* in a second legitimately so I don't think its the bypass plus the ECT is Dancing High and Low
IMO if the bypass failed it would be high temp BUT more of a steady high temp not Drastic change in a second or two of 35*


Your ECT gauge on the dash is Instant reading
the SGII takes 2-3 seconds to update so its Missed and looks more steady you can set the SGII update rate to fast

 

Oil cooler replacement does not change the bypass valve. You must change the oil cooler cover to change the bypass valve. Idc does not come as a stand alone part. However, I wouldn't be looking at the oil cooler bypass valve a the prime suspect.

262 is pretty high for eot.

Does the truck work real hard to pull the boat? His big is the boat? The reason I ask is the oil cooler bypass valve may be more active during times of high oil demand (heavy towing). But I'm talking about sustained 85% engine loads. I doubt a boat (unless it's a 30 footer) would cause greatly elevated eots.

As Blade asked. When the ect gets to 220, the fan should be going full blast....and you will definitely hear it. If the fan is not kicking in, either your getting a false temp reading on the ect, or your fan clutch is not working, or both.

My first thought is you've got a screwy eot sensor at elevated temps (swapping may verify this) and the ect fluctuation is a separate issue with either scan guage or wiring.

 

Blade & Bryan - I'll see if I can clarify a couple points. Let's take the EOT first. This gauge does not act funny, it simply shows high EOT. The boat is a 27' pontoon. With trailer it's about 4500 lbs. The truck tows it ok but up hills it grunts a fair amount. This is the first 6.0 diesel I've had so I'm not sure how much its working. I will say that before the rebuild, the EOT didn't seem to get high like this but honestly, I wasn't paying that much attention and it went to the rebuild shop right after I purchased it. Without pulling anything, the EOT can be 230 running down the interstate at 75/80 mph. ECT maybe 200/205. So, I had the mechanic change the oil cooler 3 weeks ago but nothing changed.

In the middle of trouble shooting this EOT, I started pulling a flatbed trailer with hay or my boat. Last weekend while pulling the boat, I heard the "ding ding ding" on the dash telling me to check gauges. The Scan gauges were about the same - reading 205/240. When I looked at the gauges, the coolant gauge started to rise (delayed from the ding sound) and went to the max. I pulled over and opened the hood. Coolant level appeared to be fine and I slowly released pressure from the degas bottle. There was not overflow or spewing. Got back in and cranked it up and the coolant gauge was back to normal. No issues the rest of the trip which was only about 30 minutes of easy driving. Yesterday this cycle repeated itself going up the interstate with the boat. Ding ding ding, the gauge rises up to the top, I pull over and check it out, and no sign of overheating. The scan gauge was showing 205. However, while watching the scan gauge I noticed it occasionally jumped to 245 and back to 205. If I turn the key off and back on, the dash gauge returns to normal. Go down the road and it happens again.

I can't remember the fan coming on to be honest. It was replaced during the rebuild. At this stage, I haven't been able to verify that the engine is really that hot. Since the dash gauge goes from looking fine to rising rapidly to the top but the scan gauge shows normal - combined with no overflow from the degas bottle, it doesn't really seem like its that hot. After spending 5k to rebuild, I'm nervous though.

So, is the high oil temp and flakey coolant temp related? Not sure. I'm tempted to change the thermostat and both sensors this week and see what I learn.

 

Pulling 4500lbs should be like almost nothing. Does it downshift going up hills? Have you checked DTCs? Any boost related codes? Any smoke?

Its also hard to believe you've entered the PIDs wrong in SGII since you've had it a while, but have you checked them yet?

Like you, I find it difficult to believe you are really running that hot and suspect the eot sensor and some kind of qwerk on the ect reading. Could be a wiring issue too.

Switch sensors and if nothing changes, it's not the sensors.

 

It might be worth 25 bucks to buy a new temp sensor and swap it to rule it out. And if nothing changes you have an extra sensor. Oil and coolant utilize the same part number.

FORD OEM 6.0L V8 COOLANT TEMP SENSOR 3C3Z-10884-AA

Did you do the cold soak to compare the sensor readings before starting? What were the results?

 

This has me intrigued, I thought the engine started defueling at about 250-253 oil temp but it's not. Coolant temp jumping around could be explained by air in the system but not the oil. You could try putting a thermometer in the degass bottle when it over heats and you relieve pressure. I think a grill thermometer would work. Just thinking out loud.

 

I never seen any poster that hit a defuel point don't report any power loss


I believe you would only see it with a FPW or EGT GAUGE

 

Thanks Benny, I've never had one but that's what I've read on here several times. Watching :-)

Edit: after thinking for a minute, if he's not defueling then that tells me the sending unit or gauge is wrong. Right?

 

Good chance he is defueling it's just not enough to notice

FPW should be shortened during defuel truck may even downshift to get rpm up to help cool things

I. Never saw a post when a person hits a defuel point and mentions loss of power defuel is suttle