Air cannot just get drawn into the system. You are losing coolant somewhere. It is either leaking externally or internally (head gasket, cracked block) and going out the tailpipe.

You would be suprised how much coolant can leak from a water pump or radiator without ever seeing it running on the ground.

 

Check your hoses for leaks, and check the driver’s side carpeting for wetness.

If wet, your heater core is leaking.

Odds are you’ve got a leak at one of your hoses that requires either a gentle tightening of the clamp or the hose is EOL and needs to be replaced.

Take a look at your thermostat and look for any dried residue around it. My housing was leaking slowly but not enough to drip all the way down.

 

Thanks for your responses. I've definitely got to check for a blown head gasket. The coolant so far is clear yellow and I check the oil weekly but haven't seen anything milky on the dipstick. I gotta take off the radiator cap and see if there are milky deposits and I also need to start the engine cold then remove the coolant reservoir cap to see if there are bubbles in the expansion tank (indicates exhaust fumes in coolant). I don't remember seeing lots of white smoke coming out of the exhaust pipe on cold starts but I'll keep an eye out from now on.
Actually, from reading other posts apparently the blue-green reservoir caps can wear out and cause problems. That would be the easy solution.
Just to add to the mix. I need to do the JRL Resonator Delete. The muffler system's resonator is shot and falling apart. I was underneath the car the other day trying to wire it together to make it through the winter. It's currently leaking exhaust fumes into the engine bay on start up. Would it be possible for these fumes to be pressurizing the cooling system?
The weird thing to me is although I may be loosing a small amount of coolant, the reason why I'm getting the Red Triangle for low coolant is because pressure appears to be forcing all the coolant out of the expansion tank, thus triggering the low coolant message. When I stop the car and release the pressure by cracking the cap, the coolant returns to normal levels and no warning message. Would a leaking hose, bad thermostat or a faulty cap cause this pressure build-up? I guess a small break in the head gasket would do this.
When I get more info I'll post back.

 

Thanks for your responses. I've definitely got to check for a blown head gasket. The coolant so far is clear yellow and I check the oil weekly but haven't seen anything milky on the dipstick. I gotta take off the radiator cap and see if there are milky deposits and I also need to start the engine cold then remove the coolant reservoir cap to see if there are bubbles in the expansion tank (indicates exhaust fumes in coolant). I don't remember seeing lots of white smoke coming out of the exhaust pipe on cold starts but I'll keep an eye out from now on.
Actually, from reading other posts apparently the blue-green reservoir caps can wear out and cause problems. That would be the easy solution.
Just to add to the mix. I need to do the JRL Resonator Delete. The muffler system's resonator is shot and falling apart. I was underneath the car the other day trying to wire it together to make it through the winter. It's currently leaking exhaust fumes into the engine bay on start up. Would it be possible for these fumes to be pressurizing the cooling system?
The weird thing to me is although I may be loosing a small amount of coolant, the reason why I'm getting the Red Triangle for low coolant is because pressure appears to be forcing all the coolant out of the expansion tank, thus triggering the low coolant message. When I stop the car and release the pressure by cracking the cap, the coolant returns to normal levels and no warning message. Would a leaking hose, bad thermostat or a faulty cap cause this pressure build-up? I guess a small break in the head gasket would do this.
When I get more info I'll post back.

I would test your coolant for combustion gases.

https://www.napaonline.com/en/p/BK_7001006

 

Get your coolant tested for exhaust gases. If nothing, you can go ahead and buy a new Volvo expansion tank cap. Or the whole new tank.

 

Thanks, everybody. OK, so just did a quick check. There's no milky residue on the oil dipstick and the coolant is clear yellow. With the engine running and the cap off the expansion tank, I'm not seeing any bubbles in the coolant. I'm not seeing white smoke in the exhaust.
Tomorrow I'm gonna get underneath and check all the hose connections/look for leaks. I've also got to look into my exhaust issues, my resonator is falling apart. If everything looks good, I'll probably order an OEM reservoir cap. If that doesn't work, then I gotta think more about a head gasket situation. I'm still not certain how much coolant I'm losing so I'll try to monitor that closely.

 

Thanks for the link, dmklip. I've seen a demo of that cylindrical tool placed in the top of the radiator after the rad cap was removed. For our P2s, would that tool be inserted into the top of the expansion tank with the cap removed? Have you used it yourself?

 

Is it me or is the coolant meant to be blue/green.

 

Probably has universal coolant in it, its almost always yellow.

 

I suggest that you stop focusing on head gasket issues so much until you check it for external leaks. Pull your splash sheild down and look for wetness around the bottom of the radiator and lower hose, the crank pulley and up top look at your hose connections and thermostat housing. Unbolt your reservior and check the bottom of it as well.

Don't jump to conclusions until you cover the basics.

 

Volvo coolant is green

 

Well, folks, its Zerex G05 which I thought was an acceptable replacement for the original Volvo fluid. When I purchased the car, it had greenish coolant in it that I quickly replaced with the Zerex, thinking the green color was the cheaper stuff. But actually maybe it was the proper Volvo OEM coolant though I'm remembering it more as a green color vs. blue.

On to more pressing matters. I stuck my nose into the coolant reservoir and yes, I can smell an exhaust aroma. I don't have bubbles but I did see vapor rising out of the tank when the cap was removed. I took a sniff and it smells like exhaust. This apparently is a sign of a blown head gasket. Yeah!

This morning I did a check of the different coolant hoses. The connections all felt tight and I didn't see any wetness or leaks. The area around the expansion tank is also dry but I didn't think to look around the water pump so that's on the to-do list. FWIW, the exhaust exiting the tailpipe isn't white and I didn't find any exhaust leaks around my rusting resonator which is starting to separate and come apart.

I still don't have a feel for how much coolant I'm losing. I've added fluid but that was after some coolant flowed out when I unscrewed the cap while under pressure. Today I had to pull over during a short drive after a Low Coolant warning. I waited maybe 45 minutes until the fluid depressurized and then topped up to the MAX mark. Now I've been home a few hours and it looks like the coolant I added has increased the level in the expansion tank to above the MAX mark. I'm not so sure my problem is loss of coolant as much as it's a buildup of pressure in the cooling system which forces the coolant out of the expansion tank, thereby triggering the Low Coolant, Stop Safely RED triangle.

I've got a new expansion cap on order that I'll use once it arrives but I'm not sure what effect it'll have. Someone with a better understanding of how it works can maybe tell me if I've got this correct. The Volvo cap pressurizes the cooling system and is rated for 22 psi/1.5 bar. Does it regulate and maintain the pressure at 22 psi by allowing air to escape when the pressure exceeds 22? If so, why is so much pressure building up in my cooling system that the fluid is being compressed and driven out of the reservoir? Is this an indication that my cap isn't working correctly? Or is the pressure created by the exhaust gases too much for the cap to efficiently purge from the system?

Thanks everyone. I guess I'll have more news once the tank cap I ordered arrives. Then I'll start to think about those different additives which will "fix" a blown head gasket. I guess it can't hurt to try at this point.

 

with the engine cold unscrew the coolant cap, if its pressurized even when cold you probably have a head gasket problem.

do this test as a follow up,
take the old coolant cap and drill a hole to accept a hose, any hose around 1/4 inch is fine just make sure its a snug fit.
have the inserted end of the tube sitting above the coolant level.
fit the cap, start the engine , put the other end of the hose in a bottle of water. watch for bubbles, some bubbles as it warms up are normal, if the bubbles in the bottle increase with rpm thats gas fumes in the cooling system.

next step to verify the diagnosis is a compression test.

 

2.5T has MLS gasket, which can't go bad. It's either block or the head at this point. I'd be looking for a replacement engine, at least be ready for that option.

 

What disappointed the 2.4 L diesel D5 as well?

 

vtl, appreciate the info. I was thinking I'd give a head gasket sealer a shot. I may not need this XC much longer so why not spend $50 on a sealer if there's a chance I can get 1500 more miles out of it. Any thoughts?

 

You will loose your heat core almost immediately, radiator a few weeks later.

Pinch a hole in the expansion tank's cap and drive like that till it dies completely.

 

I've got a new cap on order so I can play around with the old cap. If drilling a small hole through the top of it will release the pressure building up in the expansion tank, that's worth investigating. It's similar to gerard's idea of putting a plastic tube through a hole in the cap. By the way, gerard, I went out to the car this morning and unscrewed the reservoir cap. No air escaped so the coolant wasn't under pressure. I've gotta look into what's involved with a compression test.

 

Hey @Xfingers - how did this journey end up?

Yours looks like very similar thread as the one here (still not resolved): https://www.swedespeed.com/threads/cooling-system-issues-pressure-builds.674757/unread

 

Thanks for the link, jacek, very interesting. Looks like they've tried a few things but still getting serious pressure buildup in the cooling system. Keeping in mind it's a different car (2016 model), here's a few of my takeaways:
-Owner hasn't been able to identify combustion gases in his coolant and he's not getting a CEL. When I remove my radiator cap and the engine's running, I can definitely smell exhaust fumes. Also, sometimes I get a rough idle and CEL (misfire on various cylinders) when I start the car. In a thread, one poster said the volvo cooling system design can make it hard to detect combustion gases.
-Posters who haven't had direct experience with this problem suggest an air blockage/leak somewhere in the cooling system. While I wish this was the case, I've drained and refilled the coolant a number of times on my two XCs and never had any problems afterwards. Yeah, you have to top up the coolant reservoir once or twice, but that's about it. I haven't found any coolant leaks on the ground, at the hoses, inside the passenger compartment, or around the water pump. This seems to be the same for the OP in the linked thread.

My "solution" at this point has been to crack open the radiator cap a tiny bit to relieve the pressure and then leave it in this slightly open position (I made a mark on the cap and tank at this "optimum" position). I've put a little over 1,000 miles driving like this and maybe every 10 drive cycles I have to add a small amount of coolant to bring the level in the reservoir back to MAX. I'm guessing this loss might be from coolant leaking into the cylinders and is the reason for the rough idle/CEL which happens on about half of the startups.

I don't like engaging the trans with the rough idle. To get rid of it, I let the car run a couple of minutes then lightly increase the pressure on the gas pedal until the RPMs climb to about 2,000, hold it there for 15 seconds, then slowly ease off the pedal until it's idling at about 750 rpm with my foot completely off the gas. If this doesn't work, turning off the car and restarting will get rid of the rough idle. Right now I'm experimenting with a new procedure: When I get the rough idle on start, I let the car do its normal procedure of fast idling at about 1300 rpm then reducing to about 800. At which point, I'll turn off the car and restart and hopefully get the nice smooth idle with no misfiring.

This car is still a pleasure to drive. I haven't noticed any loss in engine performance at this point. The rough idle is probably a sign of more bad things to come and no way will it pass an inspection next August with the CEL. I've owned this 2007 XC70 for about 7 years and have never overheated it to my knowledge. This past summer before I noticed this issue I floored it once from 0-65 mph and I got a burned oil smell afterwards. I remembered the old "italian tuneup" procedure and didn't think much of it.

Some people have suggested maybe a failed thermostat. I'd love this to be the case but then the cylinder misfires would have to be a different issue? Thanks everyone for your interest and input!

 

Have you checked what you have in the cylinders? Any amount of coolant in cylinder washes it out completely to a shiny surface.

 

I haven't removed the spark plugs to check. My poor excuses are it's cold outside and I've never removed plugs before. I'm thinking if I start moving around old wire looms, disconnecting ignition coils, etc. later when I put everthin back tugether, something won't be working right and I'll have another issue to deal with.
The last time I read codes, it showed misfires on three different cylinders. And on the rough starts the CEL flashes so I guess those misfires are happening during startup. Once I get the engine to idle smoothly, she drives beautifully.

 

I had the same happen to me with a volvo 740 4 cyl. The head was cracked.
It had a pressurized tank when cold, wet plugs in the morning, took a minute of idling to clear them and run on all cyls.
It laste quite a while like that, it gets bad when you have to stop on the way to work to add coolant.
I dragged it out long enough to buy my current V70.

 

In my experience so far, the LOW COOLANT message with the red triangle (because maybe the combustion gas pressure is pushing coolant out of the tank to below the MIN mark?) is the big thing to be avoided. When this happens, I pull over with the engine running and crack the reservoir cap until the fluid level reaches the MAX mark, then drive on. This usually results in a major loss of coolant with the level around MIN after the engine has completely cooled.
What's working for me at the moment is to slightly unscrew the reservoir cap (somewhere around 1/8th of a turn, found by trial and error) to allow the combustion gases to vent while driving. I've still gotten a few LOW COOLANT red triangles, but mainly I just have to add a tiny bit of coolant every week or so to keep the level at MAX.
Oh well, it's a shame, I guess she's on her last legs.

 

UPDATE: Well, it's pretty clear to me that I have a leak somewhere in the head gasket/engine block that's allowing exhaust gases into the cooling system and coolant entering one or more of the cylinders. I get a lot of rough idling/misfires on startup and my CEL is on. Car is due for inspection in August and no way is it gonna pass.

So I've decided to roll the dice and try one of the several head gasket sealer additives available at your local autoparts store. After a fair amount of online research, I went with one of the cheapest options: K&W Block Seal and followed the method described by Austin of TrustMyMechanic:

. Austin says his garage has used this product on hundreds of vehicles over several decades with an 80% success rate doing his special procedure (instead of following the directions on the can).

First I drained and flushed the old coolant. K&W isn't compatible with antifreeze so you have to remove as much coolant as possible. After the fourth flush using tap water with the heater controls turned to full HOT, the coolant coming out the radiator was totally clear (although it still reeked of exhaust). So I flushed a fifth time just to be sure.

I mixed the can of K&W into 3/4 gallon of hot distilled water which I'd heated up on the stove burner. Our volvos don't have radiator caps so I removed the top coolant hose from the radiator and poured the mixture directly into the radiator. The radiator slightly overfilled before using all the mix; I probably have about 12 oz. left over. I then reattached the top coolant hose and filled the overflow tank to the MAX mark with distilled water.

I started the car with the reservoir cap off and let the car idle for about 15-20 minutes. I was able to add maybe a cup of distilled water as the level in the reservoir dropped. Per Austin's instructions I took the car for an easy 15 minute drive. The next morning the coolant level was at the MIN mark so I topped it up with distilled water. When I started the car, it fired up with no misfires.

Austin recommends you drive the car for 500 miles with the K&W mixture before draining, flushing and replacing with regular coolant. I drove about 100 miles yesterday with no misfires. Also the backfire I was starting to get every time I took my foot off the gas seems to have mostly disappeared. After four good starts with no misfire, the CEL has turned off and the car is now running as well as it ever has.

The preliminary results would indicate the repair is working, at least for now. No CEL means the car stands a good chance of passing inspection although it still needs exhaust work. I'm driving around with the heater controls set on full COLD hoping to minimize the K&W mix's flow through the heater core. My concern, of course, is that the sealer could end up plugging the radiator/heater core. Austin recommends not removing the thermostat and states he's not had an issue with K&W fouling up the cooling system.

So now I just need to drive another 400 miles, watch the coolant level, be careful not to overheat the engine (since the radiator only has water in it), and hope the CEL doesn't come back on. If the engine continues to run great, maybe I'll flush out the K&W after 250-300 miles instead of doing the full 500 miles. We'll see...

 

I'm driving around with the heater controls set on full COLD hoping to minimize the K&W mix's flow through the heater core.

Does not matter. It flows as it flows, always. Hot, cold, doesn't matter.

 

Thanks, vtl. I kinda had that feeling.

 

There are a few models of vehicles out there that do have a vacuum controlled valve that shut flow to the heater core. P2 volvo is not one of them.

 

Is your transmission cooled via the radiator? If so, you could be losing coolant into the transmission?

 

I can't rule out that possibility but the trans shifts beautifully. The rough idle at startup with misfires is throwing a CEL and leads me to believe coolant is entering cylinder(s) thru a leak in the block or head gasket. This dang car drives so well once it's warmed up I hate to give it up but if it won't pass inspection...

UPDATE: Unfortunately, the old girl has done some backsliding. The rough idle at start has returned along with the CEL. I haven't seen a loss of coolant yet so maybe the sealer has done some good, still too early to tell. Reading the codes, VIDA shows misfires on multiple cylinders. I need to clear the codes and see if the misfires come back for all or just one cylinder. If the car continues to maintain a steady coolant level, possibly another issue is at play like a faulty ignition coil. This would be hard for me to believe, though, because the car drives very smoothly. In short, steady idle on startup no CEL; rough idle at start CEL is back on.

For two days now, I've started the car and let it idle for 30 minutes with the K&W mix then let it sit for 24 hours. This is more akin to the directions on the can. Today I'll take her out and run some errands, building up to the 500-mile run cycle recommended in the video above. So far I've got about 100 miles since adding the sealer.

 

I followed your thread a while back because I had similar symptoms as you. There was tons of "air" in the cooling system and I had a rough idle. Sadly, I will never know what the issue was, because my engine got replaced under warranty. I had major oil burning and cylinder wall scoring. I tried exhaust leak detectors several times, but they never showed CO2 in the coolant despite it smelling like exhaust. Keep us posted!

 

Thanks for the response, 2016v60t5. I haven't used a leak detector to test my coolant but I'm surprised with your situation the fluid didn't change color. Quick question: did your rough idle smooth out once the engine warmed up and then the car drove fine afterwards? This is my situation.

Well, today was a better day for my XC70. There was a slight stumble in the idle after startup this morning but then running errands the car started 3 times with a nice, smooth idle. The CEL is still on but if past experience holds, a few more good starts and hopefully the CEL will turn off. The coolant level still looks to be holding at the MAX mark which I'm taking to be a good sign. Before using the sealer, one trip around town and the next day the coolant would be at the MIN level. I'm also not getting the strong smell of exhaust fumes when I stick my nose in the coolant reservoir when the car is idling.

My best guess at this point is that the K&W sealer seems to work best when the car is left to just idle about 30 minutes with the cap removed from the coolant reservoir. Then let the car sit for 24 hours to let the "liquid glass" cure after it's filled up the leak in the block/head gasket. This approach follows the directions on the can (except K&W says to drain the sealant mixture before the curing process).

This car isn't a daily driver so I might repeat the process of letting it idle for 30 minutes in the driveway then sit for 24 hours to let it cure. I've got a lot of hills around here so maybe some heavy accelerations blew out the repair the first time around. And this may be my situation. The sealer holds at low idle but under more intense driving conditions the plug gives way. Thanks for the interest and I'll keep updating this thread when I have new info!

 

I think it got better as it warmed up, but the car would also overheat and spew out coolant pretty frequently. How is your expansion tank cap? Is it still under pressure if you let it sit for a day? Definitely try light driving for the sealer. Avoid hard accelerations. I'm not sure how good idling is, it takes a really long time for oil and coolant to get up to temp when it's just sitting under minimal load.