Differences Between Expansion Tanks & Overflow Tanks in Automotive Cooling Systems

I have a 2014 Volvo v70 D4 that I just bought and I get a low coolant warning light that comes on after driving an hour or so. The temp gauge doesn't indicate overheating and the car runs awesome. I will then pull over and open the hood and sure enough the coolant is low. Here's the strange part, when I turn the cap slightly, coolant rushes into the reservoir, fills back up and the warning light goes off. I have to do this every 20 or 30 miles.


Also, when the car is completely cold and has not been driven for a day or so, when I unscrew the cap on the reservoir, air rushes in and the coolant begins to rise?

You know what really seems suspect! A radiator cap underneath plastic! Really think some people design some things to be dinks!

So here is my problem i have a 2006 Daihatsu sirion and it had a coolent reservoir like the upper one but without a connection under it so it has one tube on the cap and that's it and i don't understand it

I just want to say thank you. I bought a car with an expansion tank and NEVER could find anything like your video to explain WHY I didn't have a radiator cap and what more, how each was used. Bravo! 👏❤

When adding coolant to an expansion tank while the engine is cold, do you fill until level is at min, max, or in between the two?

My exspansion tank or so I think it because there is no radiatorcap on the radiator, will not pressurize at all but if I put the cap on it will throw out some antifreeze. I don't know what's going on? Plesae help. I tried to text it with a pressure gauge but it won't take any. I don't see a hole or a crack in it at all.

One question. Is the level of warm coolant higher or lower then cold coollant. Because the level in the expansiontank looks as it is rises at warm temperature en lowers at cold temperature. Is this correct?

Nice explanation

I have a 454 everytime i use it for bit then turn it off it always leaks water I always have to fill up the radiator w/ water b4 i use it, it doesn’t drain all the way just a bit after a couple uses it gets pretty low any ideas on what i need

I have downflow radiator and stock overflow tank. Can i put a swirl pot sir? What are the benefit?

May I ask if hoe to bleed the expansion tank? Thank you for your time

Excellent video.

I have a lengthy question. On my 5.3 swap in my 64 C-10 I installed the surge tank from the 03 Tahoe the engine came out of but not the radiator. I also installed the correct heater hoses to the surge tank. My problem I essentially have two radiator caps now and I can't seem to get the air out of the system. Running the vent line under the radiator cap of my LS swap aluminum radiator to the outlet on the surge tank that normally goes to the stock Tahoe radiator. I'm doing this via a reducer in that line. Thank you for taking the time to read. Great video BTW 👍

i replaced the radiator, with a new one the water pump and thermostate in my 09caravan
coolent level drops and does not get sucked back into the radiator, i must add coolent to radiator to keep it from overhaeting. no white smoke no coolent in oil what should i be looking for van has 149k i am thinking vally pan gasket

I am thinking, for the pressurized system, if I release the pressure when coolant is hot with care, then when coolant is cool, it'll create vacuum. Next time it gets hot again, the PSi won't be as high as usual. Is this a good idea to have constant vaccum in coolant line? I've seen coolant hoses got blown holes in them. The goal is to prreserve the coolant hoses. Thanks

Great 👌

Regarding the overflow tank (bottom diagram) if the cap is "flimsy" and not pressurised, how does any pressure become greater than in the radiator to push coolant back into the radiator? Also if the radiator cap has cooled would that not close off the valve thereby preventing any coolant pushing back from the overflow tank? Not arguing, just confused🙂

Can I convert an expansion tank style to an overflow? I ask because I have a Power Stroke with an expansion tank (degas bottle) in a very inconvenient spot.

Does the position of the overflow tank matter? let's say i want to move the one that came with the car, do I have to put it higher/lower than the radiator or can i put it wherever? Thank you!

Can you flush and REFILL coolant through the expansion tank (top picture) because my car does not have a typical radiator cap??!

Can i install an overflow Reservoir to a system that uses expansions tank?

Great vid. My Cap seal broke and fell into the radiator, causing my overflow to leak a lot of water. Should I worry about the seal being stuck in radiator and obviously I need a new radiator cap? Thanks!

Great explanation - thank you.

Great explanation

Thank you ! great info!

On the expansion tank explanation, you mentioned that some systems have a return line. I'm wondering if you have any examples of systems that don't have a return. Seems like across the board if they have an expansion tank they have a return to somewhere just before the pump.

I don't really know why they need a return, but it has to be doing something. Maybe keeping some small amount of flow up and through the tank continuously purging air?

Help!!! I have a Jeep Gladiator and suffered a major brain cramp and added a small amount of Dot 3 brake fluid to the expansion tank which is right next to the brake master cylinder fill. I immediately realized my mistake and siphoned all of the mixed coolant and brake fluid from the expansion tank. I also filled the expansion tank twice with clean water and siphoned completely to hopefully flush the contaminated content out of the expansion tank. I then filled the expansion tank to the proper level with pre-mixed Mopar OAT coolant per spec. My question is, could any of the brake fluid be still in the system. Note the engine was cool and never started during all of the above.

Question, my truck had an expansion tank from factory and switched to an over flow style tank from a 90s-2000s mustang. Since there is no way for the pressure to be released could this be the reason for coolant pushing past the overflow tank cap and spraying out when I am racing for one consecutive long time/run? Doesn’t over heat or anything just pushes past the cap when i do lets say a 60-130mph runs.

So does placement of the overflow tank matter then? Or is it traditionally lower than the radiator

Nice video, thank you.

My golf v has a wire inside the expansion tank. When I overfilled it I used a cloth to soak up and pulling it out it bent the wire up. I bent it back. What is it for and will it cause a problem later?

I have a 2012 GMC sierra. Does the coolant circulate through the expansion tank is my question… Just added some coolant after I fixed a radiator leak and I want to make sure that the proper ratio is flowing through the system. It still looks like pure coolant on the expansion tank, even after driving for a while…

In the upper system with the main cap on the plastic bottle can i add another tank to match the other system and to refill the the system if needed

I have question what If I filled the resovoir with one jug a pure antifreesze and did not mix.Can I still fix the mix to get right ratio?

I see in my mom's Hundai Starex it has an expansion tank system built to it. I suppose it's normal to see the coolant boils while the engine is running, correct?

Great explanation. I had wondered by my BMW could have small hole built into the top of the coolant tank, when most websites I saw said that the coolant tank is pressurized and part of a closed system

thanks

hey man what happened if I put a little more coolant in flow tank?

Bravo..

On the expansion tank, where does the lower hose go?

thank you sir.

I have a sonic 1.4 and the reservoir tank cap say 20psi so if i use a 16 psi cap Is any problem with that or could be a good thing???

wow thank you for the valuable info, please consider explaining the internal chambers to expansion tanks as I have a 2018 Nissan Frontier v6 crew cab and noticed after playing with the levels in radiator and expansion tank that there are 3 different levels, or chambers in my whitish semi-transparent tank, first closest to line from radiator, a small rubber hose about 3/8 inch ID was about 2 inches above max line and only about 1/4 of tank area, then near the middle of tank a 2nd chamber that was about 1.5 inches above max line covering another 1/4 of the tank area, then a 3rd chamber in the remaining part of tank, the back half that was about 1 inch above max line. I have search high and low on the internet for this info, breakdown but have failed. I think you are more in tune with the proper resources to supply the explanation, I hope.

Why does it say on the manual not to add coolant if the expansion tank is empty. Air could enter the cooling system and damage the engine. What are the chances of that happening?

Great thanks!

Perfect explanation. Thank you for making this video

Does the overflow have to be vented or can be completely sealed?

If you have a low mount radiator with an expansion tank that links to a thermostat housing/fill neck - what PSI caps would go on the thermostat housing and expansion tank?

Eg if 16 psi cap is normal - would I do 8 and 8 in each location or 16 in each?