2016 3.5l Ecoboost Coolant Fluctuation

[Brandonian]

Howdy Again Everyone!

Well - here I am again for some friendly advice. 2016 Expedition EL XLT with 3.5l (that's all they made for these years anyway) -

Coolant temperature readings have become erratic (it appears to warm up fine, temp creeps above the "C" mark on the gauge when I run it via remote start for a few minutes - I get in, drive the kiddo to school, normally by the time I get home from drop off a mile or so away the gauge is reading to temp. However I recently noticed that driving it my temperature appears to fluctuate wildly - I.E. on a downhill my gauage drops drarmatically, going uphill it gets back up to temp - then driving it more it goes down a bit. Sitting at Idle in front of my garage - it was fine (I even revved it a bit to see if I could fluctuate it at that point) and it didn't fluctuate.

Now - I normally didn't watch the temperature gauage - but I've never known this to be normal activity by any means. It's not overheating, it's not overcooling - just an odd fluctuation.

For informational purposes - the secondary water pump was replaced when I purchased it by the dealer, I replaced the primary water pump 2 months after buying it because it was leaking badly - and I threw in a new thermostat while in there (this was all last summer).

I wouldn't say it's cold enough here to really do anything of this nature wise, it's low 30s these mornings. My heat works fine (I have to turn it all the way up when the kiddo is in the vehicle, she's a wee little one and says she's cold lol) - when I turn it back to auto on say, 72 degrees, it helps with the fluctuations - checking the reservoir I don't see a loss of any coolant. Which is why I'm believing stuck open thermostat related - but if the thermostat was stuck open I'd have an issue with heat and it wouldn't go back to normal temp just sitting there idling?

The one person I could always call on to help is no longer walking this plane - and my knowledge of general mechanics thanks to him allows me to follow procedures and repair most anything - however sometimes I really get stuck in a diagnostic phase. He could put his ear to a screwdriver on the parts and tell you what was wrong haha .

Also I dislike working on these Ecoboosts - while not mechanically difficult, everything takes longer and is a pita because of the turbos and so many vacuum lines, electrical - i am really contemplating trading this in before any other issues stir up and getting just a normal V8 burb to work on. I'll work on my Wife's V6 Ram all day because of it's lack of turbos, but when it comes to the Expedition, ugh. I would rather own a Ford than a Chevy - but jeez. Anyone else have similar experience - takes them that much longer to do things on this?

 

[Adam J]

another diagnostic concept would be to get a "real" coolant temp reading through OBD and consider the temp "gauge" on dash is likely more of an electronic readout, calculated by input from perhaps an erratic sensor? brief research seems to indicate the $30 sensor is on passenger rear of engine. perhaps on cylinder head below vacuum pump? https://www.f150forum.com/f118/location-cht-temp-sensor-3-5-eb-430813/

 

[Pilgrim]

I had something similar a few years back on my '15. Turned out to be a bad sensor. Plugging obd scanner in didn't help, because it just reads the temp from the same sensor.

 

[Darkhorse16]

Only two things that come to mind:

A faulty sensor (which has been stated);

Or if your new thermostat isn’t functioning properly such as sticking open (which you mentioned). It’s not common but thermostats can fluctuate between not closing when they should as well as not opening when they should.
This is usually debris or blockage related.
I’ve only ever seen it when someone got overzealous with gasket sealant while trying to prevent a coolant leak on the thermostat housing. Some of the sealant got into the pass-through on the thermostat (that little hole that lets small amount flow through for pressure equalization) and more of it interfered with the center and the springs.

All that said if your gauge and a scanner both show the fluctuation, but there are no other signs. It is probably the sensor.

What do you mean by secondary water pump? I’ve never heard of that…

 

[Brandonian]

Thanks for your responses everyone...turns out I've been diagnosed by my closer friends has having anxiety related to issues and just watching everything like a hawk and listening to it too closely reading into things that aren't there.

To reiterate - the temp fluctuation was normal as it was very short drives - and it appears I just never paid attention to the issue before and was not letting it get warmed up all the way, school drive is a mile away - I drive my 8 year old there, and then back home - sometimes I let it run remote start for a full 10 min (she's a teeny bopper and hates the really cold leather seats so I try to warm it up a little for her) - but anytime I have driven it outside of that instance my temp reaches normal and doesn't move.

The dealerships informed me of two water pumps on these - I guess one is internal and one is external? They replaced the internal one when they got it on trade, and I replaced the external one when it leaked everywhere two months after buying it. It was at that point I realized I do not like working on these because of all the extra work involved with vacuums and turbo lines. I also looked up the ford parts and it does list two water pumps for it oddly enough. Still debunking that lol.

I'm now fighting other small things - potentially the valve cover leak and the vacuum pump leak, although when I found that the top vacuum line for the TB was never plugged in (dealer tucked it away and down in the side under the coolant reservoir when they did their water pump replacement) I plugged it in and I don't get any smells or fluids now- and if I should be looking to trade this and get back into a normal V8/V6 non turbo scene, or if I should just keep it, and just take the extra dive in parts costs and time costs personally. It has 150k, I bought it about a year ago with 147k or so (working from home it doesn't get driven daily for long distances, just very short ones).

I like the power of it, I like the sounds of turbos - I miss the simplicity of a normal engine (normal to me anyway lol) and having the grumble of a V8 to listen to.

For reliability - at this 150k mark - ya'll think I just push through with little repairs - or am I on the cusp of having some major crap happen? I don't have a crap-ton of money to dump in a mechanic I don't trust...I also don't yet have a house with a 2 post lift to make life easier for me (in the future plans lol) - I'm mechanically inclined - but with 4 kids, full time beyond work, and our hobbies - I don't want something in my driveway that I'm going to have to constantly tear down.

My commander was reliable - 179k miles and not a thing wrong with it (outside of preventative I did) - about 1 or 2 saturdays a year I'd have it down for maintenance. But this Expedition I am quite intimidated by.

i'm hard pressed to trade just because of a couple of small repairs and up our car payment again - but at the same time I'm thinking of just going back to a 6 seater truck for us and I can tinker with it. This vehicle makes me feel like a Grandpa rather than a Dad - I can't put a small lift on it (economically, jeez at those prices) and can't put a nice exhaust, and working on it just takes 5x as long lol.

 

[Darkhorse16]

Turns out you’re right about the secondary pump.

It’s mounted on the front of the passenger side cylinder head. Never realized it was a pump, just looked like a control valve for coolant flow to the front and rear heater cores. Turns out that it does have a small electric pump inside though.

Reliability is pretty relative. I have 130k on mine, but have recently replaced a lot. But I’m extremely preemptive with my maintenance; to a fault. Add that in with a couple poor diagnostics I ended up doing a full timing job(changed most of the front end parts too), replacing both turbos, when all along it was a torque converter issue that ended up claiming my transmission. It’s a really long, painful story that played out over the last 4 months.

BUT there are plenty of people who have trouble free service well beyond where you’re at. I’d say proper diagnostics, not ignoring lingering potential problems, and prompt maintenance at the correct intervals are key.

I was cross-shopping 5.4 expeditions with 3.5 eco’s; ultimately I don’t regret the decision. The eco may have more occasional small issues, such as a coolant leak from a turbo, that’s more annoying that critical. BUT the 5.4 3v is more known for catastrophic failures. Which is why I decided to stay away since my wife plus kids are the primary users.

Don’t know if that helps