Overheating Weird - Smartest People Needed 2016 XC90

robinvolvo · Post by **robinvolvo** » 05 Jan 2025, 17:58

I have a weird issue with a 2016 XC90 T5 (spa) overheating.

* Replaced complete cooling system (thermostat, radiator, water pump, fan, all hoses, vacuum purged and replaced coolant, pressure tested cooling system and there are no leaks), yet it persists in overheating when driven hard.

* Tested coolant for CO/CO2 with one of the test kits multiple times, there is no leak so doesn't seem to be a head gasket issue, no problem with the engine oil – no milky oil, no smoky exhaust.

* I can drive all day at 40 MPH and it will be fine, if I push it harder and drive at 60 for a while, it will overheat.

* When the overheating happens the car seems to get "stuck" in overheated mode, the cooling system won't be able to get the temperature down from 250 degrees until I stop for 10 minutes with engine idling.

* When the engine overheats, the cabin heat (AC) will not work, it blows cold air only (but it works fine at other times)! I feel this is an important fact in the diagnosis, it seems to me to indicate that the coolant has stopped circulating for some reason.

If I stop for 10 minutes with the engine idling, the car somehow recovers, and flips back into normal mode, the engine cooling system starts working again and temperature falls to 200/210, immediately when that happens, the cabin AC heat kicks in again and starts blowing hot.

What can this all mean? Water pump and thermostat have been replaced by Volvo dealership, engine fan was also replaced, comes on and blows hard when engine heats up.

Post by **matthew1** » 05 Jan 2025, 18:04

robinvolvo wrote: ↑05 Jan 2025, 17:58
* When the engine overheats, the cabin heat (AC) will not work, it blows cold air only (but it works fine at other times)! I feel this is an important fact in the diagnosis, it seems to me to indicate that the coolant has stopped circulating for some reason.

You're correct that this is unusual and a clue.

robinvolvo wrote: ↑05 Jan 2025, 17:58Water pump and thermostat have been replaced by Volvo dealership...

I'm curious what they said. It was there for this overheating problem, correct?

robinvolvo · Post by **robinvolvo** » 05 Jan 2025, 19:02

Thanks for the response, history is:

1. First time it overheated, I take it to dealer, they say water pump is aftermarket (I bought car used 6 months ago), and fan might not be working correctly, they charge me a crazy amount of money to replace water pump, fan and thermostat. They warn "if overheating recurs it may be engine is damaged and needs new head gasket".

2. Overheating recurs, take car to independent mechanic who seems smart and knowledgeable, he does CO test in coolant (negative), he says this is not a head gasket, due to the test being negative and also due to "if it was head gasket you would be getting a lot more pressure pushing back into coolant reservoir", he said he has seen many head gasket issues and this does not look like one at all.

3. Independent guy bleeds and pressure tests coolant system, replaces radiator and all cooling hoses (on basis that he can't think of anything else it can be); purges all channels and hoses, tests water flows through waterpump, radiator and other hoses; CO tests coolant again; all good.

4. Through all this there have been no coolant leaks, coolant always stays fine up at above the maximum line.

5. Overheating still occurred (yesterday), which is when I made the discovery of the cabin heating not working at all when car overheated. Cabin Heat works strong and fine under normal, non-overheated conditions.

If I stick to 40 MPH / < 2,000 RPM I can drive forever without overheating.

I am speculating that something causes the waterpump to switch off at a a certain load / temperature, could something like that be possible? Some sort of bug/failure in the ECU? This is the only thing I can think that would explain the cabin heating suddenly stopping working at the same time as the engine overheats.

Post by **matthew1** » 05 Jan 2025, 19:31

I'm unfamiliar with SPA Volvos... is there a temp gauge in the instrument cluster? Either oil or engine temp.

robinvolvo · Post by **robinvolvo** » 05 Jan 2025, 19:42

There is no temperature gauge on the dashboard, I have an OBD reader I use to monitor coolant temperature on my phone. I have been monitoring it continuously when driving around. (OBD reader only has coolant temperature not oil temperature).

When I stay at 40 MPH < 2,000 RPM, coolant temperature rises to about 210 and stays there, fluctuating down depending on the load and speed. As long as I stay at 40 MPH I am ok and will stay at 210 degrees.

When I pushed harder yesterday it was fine for a while, accelerating more aggressively, driving at 60 MPH even 70 MPH, but after perhaps 15 minutes of that harder driving the OBD showed the temperature swing up to 230 then 240, then dashboard "engine overheating, reduce speed" message comes up.

At this point cabin heat stops working.

I slow to 10 MPH, OBD shows coolant at 250/240, I crawl along with minimum load on engine, after maybe 10 minutes of this, it suddenly seems to recover, coolant temp drops to 210, then quickly to 180 as cabin heating kicks in again full blast.

Weird.

Post by **matthew1** » 05 Jan 2025, 20:34

I'd probably push a little on the Volvo dealer service department. Try to make it their problem, talk to the manager -- polite but firm.

240 is hot, yes.

Let me see if I can summon a guy with SPA experience to this thread...

Post by **FlyingVolvo** » 05 Jan 2025, 22:39

Was the coolant temp sensor replaced? I read you replaced much of the cooling system, but didn't see mention of this.

The way the HVAC stops heated air during your overheat is super odd and not a behavior I'm familiar with at all. It does sort of sound electronic in nature. Usually this symptom might be indicative of a thermostat issue, but yours is new, and your heat works fine all the other times.

The SPA cars can be notoriously difficult to bleed and get all the air out of. I'm just trying rack my brain and figure out if this could be a possible cause.

This is definitely a weird one. Unfortunately my SPA experience is still pretty new... Too bad it's not a P80!

I'll keep digging around some other posts and forums and see if I can find anything like this. I also know a former Volvo tech who I'll send this to and see if he has any advice.

Post by **Krons** » 06 Jan 2025, 04:28

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.

importaw · Post by **importaw** » 07 Jan 2025, 11:53

Hi, did you get an updates on the issue?

MarkVolvo · Post by **MarkVolvo** » 22 Jan 2025, 11:56

Krons wrote: ↑06 Jan 2025, 04:28 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?