Overheating Weird - Smartest People Needed 2016 XC90

[MarkVolvo]

And BTW, I've had this thing in the garage, during the summer, with AC full blast and the doors open for 20 mins and could not recreate the issue - tested it the same way after driving awhile and it did happen again.

[Krons]

Thinking the temp sensor, check a hose under the hood with an infrared temp gun both before and after issue to ground truth your onboard temperature measurements. Can get an infrared temp gun at Harbor Freight pretty cheap.

I've got 2017 V60 with random overheating issues, but different symptoms. On longer drives when going to IDLE engine temp warning comes on. If we get moving the temp goes back down. AC warms up as well when idle and cools off when moving again. I'm not close to a dealership so I took it to a local "European" mechanic. I had noticed the fan was not coming on, even when the temp warning was on. He told me it was the fan and replaced that and the module on it. Problem came back on our next road trip some 3 months later.

I suspect the coolant temp sensor but for the life of me I can't find the thing. Does the coolant have to be fully drained to change it? Can anyone post a picture or description of where it is on the engine?

I wouldn’t know…what engine is in it?

[Oly850]

So our 2017 had a similar issue, we got a brief coolant low warning and then the car would overheat as you've described. I topped up the coolant 3x over about 10 days and finally found a cracked T fitting on the driver's side of the motor down low that had a fairly invisible crack but greenish coolant staining down the front. It's black ABS and about 2" in diameter. Dealer replaced. Service writer was a prick about it because I dropped it off on a Saturday, but it never happened again.

[MISSMYT5C30]

I have read about this problem and I am having the same problem with my XC90. The problem is a short in the ECM. Apparently you can get it repaired or replace for $1000.00 and up. I will post the link to the site.

[Vova585]

I have read about this problem and I am having the same problem with my XC90. The problem is a short in the ECM. Apparently you can get it repaired or replace for $1000.00 and up. I will post the link to the site.

That's an interesting variable. Totally likely that algorithm is somehow malfunctioning. However with the location of ECU under the fender well(so smart, probably learned from jeep) I would not be surprised for water Intrusion

[FourStar]

I have read about this problem and I am having the same problem with my XC90. The problem is a short in the ECM. Apparently you can get it repaired or replace for $1000.00 and up. I will post the link to the site.

Hi, are you able to share that link? I've got one that seems to be having the same issue. Almost like the water pump stops running at highway speed.

[robinvolvo]

Original Poster back again here, I have now also changed the temperature sensor as suggested in some responses above, and also drained and refilled the coolant again with a vacuum tool, and pressure tested the cooling system. Unfortunately the overheating problem persists.

To recap, the entire cooling system on my XC90 has now been replaced: thermostat, fan, water pump, radiator, temperature sensor, connecting hoses. The system works fine in daily driving around town, it is only on a longer journey of an hour or more where the engine has time to fully heat up and I then drive at highway speeds that it will overheat. There is still no carbon in the coolant (tested multiple times with the chemical test), no milky oil, no smoky exhaust, so doesn't show any signs of being a head gasket issue.

It seems to me, along the lines someone suggested above, that under certain conditions, the cooling system just switches off. Perhaps an ECU issue/bug.

The most recent time it overheated was this weekend, I was doing about 60, coolant temperature was fluctuating between 205-215, oil temperature was steady at around 210. Then suddenly, coolant goes up to 230 and climbs to 240, dash warning comes on, I pull over.

• At this point, as with previous overheating incidents, the cabin heat will not work, it blows cold air (normally cabin heating works fine)
• Oil temperature begins to climb now, 220, 230; I switch off the engine
• From this I surmise that the cooling system has just stopped, the coolant isn't circulating to bring heat to the heater core
• I wait with engine off for 10 minutes coolant temperature falls to about 220, restart the engine, cabin heating works again and cooling system is obviously functioning and coolant and oil temperature come straight back down.

I have looked at the Xemodex website and links regarding repairs to ECU. Do any of the posters above have more information on this ECU issue / fix? Does it sound like this could be the answer? I don't have any of the codes mentioned showing up with my OBDII reader.
https://xemodex.com/us/product/engine-c ... ir-service

[robinvolvo]

Any feedback on the Xemodex ECM process, anyone done it to address overheating issues?

Any other suggestions for this weird overheating issue? I am at a loss on what to try next.

[MISSMYT5C30]

I just purchased the XC90 and have replaced most of the cooling system. I am going to replace the ECM if I cannot return it to the dealer. This should be a recall and I sympathize with anyone else experiencing the same issues. It gets expensive.

[robinvolvo]

*BOUNTY OFFERED* to anyone who suggests a solution that ends up working

OP here still living with my inexplicable overheating problem on my 2016 XC90 spa (please read my first post in this thread).

I haven't spend $600 on the Xemodex ECM rebuild as suggested later in the thread, as I don't have any OBD codes showing anything wrong in ECM, so seems unlikely that would fix it.

One additional clue: though the coolant doesn't leak and has been replaced multiple times and refilled under pressure with full pressure testing - no leak shows up and pressure holds for an hour with the test pressure tool connected. Despite no leaks, once in a while, particularly during cold weather I will get a "coolant low switch off engine" warning, I know that can happen sometimes even with cars without any problem, but seems to happen more often to me, maybe once a month or so, or once a week when very cold. When I check coolant level (engine cold), it is never actually low, always just covering the max line, I usually put a bit more in anyway, and the warning goes away. What could this indicate? Some obstruction in the coolant flow perhaps?

My point in the earlier post that when it overheats, the cabin heat stop working, preys on my mind and seems to hold a clue to the answer.

I am stuck with a $15,000 car which works ok for my day to day city driving as long as I am careful, but I can't do any long highway trips as it will overheat. This is a real mystery, I will seriously pay a bounty to anyone who come up with a solution that works, please any smart Volvo mechanics out there read through my earlier posts and give your verdict, something very weird is happening, this is not a standard problem.

TIA.