Redbrown looking residue at the bottom of the expansion tank

[El Padrino]

I noticed there's a red/brown residue (I think) at the bottom my expansion tank. Car is a 1998 V70R. My initial thoughts were a blown head gasket. The coolant hasn't been dropping at all though.

I followed Robert DIY's advice on checking a bad head gasket via this link - https://www.youtube.com/watch?v=WXOHjePUWkU

With the engine at operating temperature, I slowly and easily unscrewed the green expansion tank cap and coolant was not gushing out. The coolant behaved as expected with no bad head gasket (as shown in the video link).

The first photo is with the engine cold.Cold engine.jpg
The second photo is with the engine at operating temperature?At operating temperature.jpg

Any thoughts what this red/brown residue could be please?

PS: apologies for the images not being the right way round.

[Bob Meadows]

How long has it been since the antifreeze was changed:~
It could be old and does not provide the required rust protection.

Flushing should help, central heating descaler is good and far better than the branded items sold.
(Central heating descaler is fine for mixed metals)

Drain the system and add the above diluted.
Bring the engine up to temperature and leave as long as you can- drain and then flush with clean water- drain again then fill with the correct strength of antifreeze & water mix.

Ethylene Glycol Antifreeze is correct for the car.

Good Luck.
Bob.

[El Padrino]

Originally Posted by Bob Meadows

How long has it been since the antifreeze was changed:~
It could be old and does not provide the required rust protection.

Flushing should help, central heating descaler is good and far better than the branded items sold.
(Central heating descaler is fine for mixed metals)

Drain the system and add the above diluted.
Bring the engine up to temperature and leave as long as you can- drain and then flush with clean water- drain again then fill with the correct strength of antifreeze & water mix.

Ethylene Glycol Antifreeze is correct for the car.

Good Luck.
Bob.

Hi Bob, thank you for your reply. The coolant was changed back in September 2023, so not that long ago. Not by me though. Thank you for the tip on using radiator descaler. What ratio of water and descaler should I use? Is it ok to put a hose pipe down the expansion tank to clear it out or best to just pour deionized water through the system?

[IainG]

Hi
If the coolant has been replaced already. Just remove the expansion tank and give it a good clean out and then see if the “rust” residue returns. You just need to suck a bit of coolant out of the reservoir so you don’t waste any.

[john.wigley]

If you think that you may have an (as yet) undiagnosed engine problem developing, is it worth having a sample of coolant professionally analysed BEFORE it is changed? This may provide an early indication of potential area(s) of concern or, hopefully, reassurance that all is indeed well and a flush and new coolant is all that is required?

Regards, John.

[Bob Meadows]

Hi:~
Most of the details are covered now by the forum response, however to answer you direct- if you are going to flush the system.

The central heating cleaner is very economical, generally sold by the Ltr. it goes a long way so you will not use all of the product as it gets diluted: best to follow the instructions on the container for the ratio mix etc.

The antifreeze is also diluted to suit your requirements and I suppose the requirements of your location (I use 50/50 mix here -UK)
Again you should find recommendations on the container.. always buy concentrated otherwise you just pay a premium for water!

Draining the system varies from owner to owner (from memory a drain tap is incorporated in the radiator base) or remove a lower hose, also check the hose clips are in good condition.. they can rust through.
You can flush through the header tank with a hose removed or other.

Tap water in my area is fine for all cars I own. Riley-Ford & two volvo (240 & V70 as yours) you may decide to use other water though depending on different things.
The advice to draw the water out of the header tank is worth a try, the suction turkey baster will be fine for this and no turkeys or chickens will object!

Hope it turns out to be a simple fix- go for basics first- good luck.
Bob.

[El Padrino]

Thanks for everyone's responses to this thread. I'll flush out the system first as a first step. As usual, the maestro Robert DIY has a good link on flushing the system - https://www.youtube.com/watch?v=LSvcEYoYNCo.

I need to do an oil change soon, so will do the flush at the same time.

[El Padrino]

Had a chance to drain the coolant today. My radiator doesn't have the bleed valve so I disconnected the lower radiator hose which released the coolant. The coolant looked OK to me, not rusty etc. At the same time, I'd thought I'd drain the coolant from the engine cylinder block. With the help of Robert DIY's video and a 'grainy' black and white photo from the Haynes manual, I managed to locate the drain plug. Reaching the drain plug to unscrew with a 13mm socket was a bit fiddly and limited space with the front of the car on axle stands, but managed it and released what coolant there was from the cylinder block. Wished the car was on a ramp during this bit.

Once the drain plug and lower radiator hose were secured, I added diluted central heating cleaner via the expansion tank until it was full. Waited for the car to get up to temperature, which only took about 10 mins. After it cooled, drained again via only disconnecting the lower radiator hose. There was no mention in Robert DIY's video or the Haynes to drain from the cylinder drain plug again at this stage. I hope that is correct. I then flushed the system with running water from a hose pipe until clean water came out. I then flushed the tap water with over 4 litres of de-ionised water and secured the lower radiator hose.

I removed the expansion tank and cleaned it with warm soapy water, to get rid of the red/brown looking residue (looks like rust) lurking at the bottom. It's spotless now, so will tell if the rusty residue reappears after the coolant has gone in. The coolant tank is less than a year old and thought I'd replace the old rubber expansion tank hoses with DO88 silicone ones from PFS (as they had a sale on). There's no record of when the thermostat was replaced, so I don't know how old it is. As a preventive measure, I'll replace it with an OEM thermostat and sensor. The two T40 torx screws holding the thermostat housing are in bad shape. I hope I don't strip them, so I sprayed them with penetration spray and will try taking them out - carefully.

After a flush and refilling, how do I burp/bleed the system to make sure there's no air in it? If so, what's the best method to do so please?

[Luxobarge]

For what it's worth I think you've done exactly the right thing in cleaning and flushing your cooling system, I'll bet it stays clean. Only exception is that if it were me I'd leave the thermostat and sensor alone, if it ain't broke don't fix it, especially the sensor, they're quite reliable. Make sure you refill it with decent antifreeze, after a full flush like that I'd be taking the opportunity to refill with red long-life coolant, I expect this is what you have done as I believe this is what they used from the factory.

In terms of burping/bleeding, I've drained and refilled my cooling system several times over the years, and not found a way to manually bleed it. However, the system is pretty much self-bleeding, so fill the reservoir up to max and take it for a spin to get the engine fully up to temperature, and you'll find that the reservoir level drops alarmingly as it bleeds itself - often enough to put the low level warning light on. Don't worry, just let it cool, top it up again and do another heat cycle. The second time it will probably need little or no topping up, and you're all good. This is what I've done and never had a problem.

HTH

[ITSv40]

Exactly as Luxo says ^^^^^^^ Just check the coolant level over the next few days and top up if necessary.