Coolant Loss Expansion Tank HELP

[matthewb0051]

Friends:

I am traveling from San Antonio, Texas to Crested Butte Colorado. So from about 600 feet elevation to 9,000 elevation. Made the trip last Saturday and returning tomorrow/Saturday.

Driving the Land Rover LR4 (aka Discovery 4 in the ROW). We had been losing coolant a little here and there in the weeks leading up. Last summer was new water pump, cross over pipe and some other fittings. No leaks there. I narrowed it down to just a small amount coming from top of expansion tank, so I replaced the cap.

The CAP was not the issue. On day 2 of trip up, we stopped at a rest stop at around 6,000 feet. Got back from the can and noticed the truck was taking a pee as well. Here's where it is gets odd for me. I noticed that coolant was backing up into the tank and pushing out the top at neck.

We stopped a couple more times as we gained altitude and no issues with coolant loss. But those stops were preceded by a reduction in speed due to being in small towns.

When we arrived in Crested Butte, I looked under hood and coolant was pushing back into tank and out top of tank. My theory is there are either cracks or the neck had been expanded to a point that the fitting wasn't tight enough to keep coolant in tank.

I ordered another tank and installed yesterday. But here's my Q: what is causing coolant to run back into expansion tank after stopping? I plan on bleeding this am to ensure no air bubbles.

New parts: tank and cap already installed.

[matthewb0051]

Truck is a 2010

[asphaltgambler]

Off the top, I would expect odd issues if the cooling system is not pressurized at temperature. Also, fair chance of air in the system. I would install the expansion tank, fill, bleed then cool down completely, fill to cold level. Then see if any issues remain.

[Scott Douglas]

For purposes of this discussion is this illustration what you're talking about?



If so I'd think you have air trapped in the engine that is causing the coolant to expand when sitting 'hot'.

[Scott Douglas]

I've had water pushed out the overflow [expansion] tank on my Alfa when the water wasn't being circulated thru the radiator properly, only super heated by the engine.

[matthewb0051]

Originally Posted by Scott Douglas

I've had water pushed out the overflow [expansion] tank on my Alfa when the water wasn't being circulated thru the radiator properly, only super heated by the engine.

Scott: you diagram... yes that's the piece I reference


New radiator as well last year with water pump

[Scott Douglas]

If you've 'burped' the system and don't think there's any air in the engine/radiator part of the system, my guess would be your expansion tank isn't big enough to handle the volumetric change in the water at temperature.

As an example, when driving my Alfa back home from pickup in Palm Springs on a 110*F day, the water was pumping out the overflow tank like crazy when we hit the freeway. Stopping at all the exits and finding water to drench the radiator, all while the engine is running, caused the water to be sucked back into the radiator/engine from the tank. It was a good lesson on how not to overheat an engine for my son. There are a lot of off ramps on the I-10 between PS and Riverside. We made it home without blowing up the engine, but my wife about blew a fuse having followed us all the way in her air conditioned van with my daughter.

[Scott Douglas]

Did you open the heater vents when 'burping' the system to make sure the heater core was 'open' to the system? I'm not sure if the LR system shuts off the water to the core or not to shut off the heat.

[matthewb0051]

Just got finished. Turned on heater while bleeding. There was no heat in truck when I got back in. Had it on for over 20 minutes and still no heat. New development as it most definitely had heat last winter.

Got a decent amount of air out of system though.

[Scott Douglas]

I think you found the cause of your problem. Now all you need to do is cure it.

[matthewb0051]

Problem solved (I think). Burped again and now we have heat.

Going to drive it around town today and ensure all systems go.

[masraum]

Good luck.

As Scott experienced, with crazy high temps, things will be hotter and expand more. I've never driven at elevation, but it wouldn't surprise me to learn that an elevation change like that would have an impact on an automotive cooling system in perfect working order.

The boiling point of water @ sea level vs 9,000 feet changes from 212º to ~195-197º. 15º is a big change, and seems likely to change a cooling system.


Another factor that also probably has a huge impact is the change in atmospheric pressure. Atmospheric pressure at 600' is ~14.4psi (sea level is ~14.7). Atmospheric pressure at 9000' is ~10.8psi. So to get similar performance out of a radiator cap at that level, if the stock radiator cap is 15psi you'd probably need 19psi at 9000'.
https://esenssys.com/esssienew/wp-content/uploads/2021/02/altitude-vs-atmospheric-pressure.png.webp

I think this is probably "normal" for the drive that you performed. When you get back to SA, I suspect you're going to need to fill the radiator/overflow.

[Rot 911]

The institutional knowledge of the individuals on this forum never ceases to amaze me.

[Tobra]

You stop, coolant gets hotter, it expands into the expansion tank

[Ayles]

Have you tried using one of these special funnels to refill? This was what I needed to fill/burp the system on my Xterra which is known to be sensitive to air in the cooling system.

https://www.amazon.com/gp/product/B00A6AS6LY/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

[matthewb0051]

^^^

Have not used that type of funnel. Sounds like what my LR mechanic described. He said they use some pressure fill to get rid of air bubbles.

His solution for me was to just continually start, heat up, burp/bleed, cool down, then do it all over again... all day.

[Scott Douglas]

Based on my experience with the Alfa, all you should have to do is cool the tank on the radiator while keeping the overflow/expansion tank full. We never shut the engine off, just got a bucket of water and poured it on the top tank of the radiator, being sure not to splash the block, and kept the overflow tank full as the water was sucked back into the radiator. My son was amazed at how fast the overflow would empty back into the radiator as it cooled down. Because of the unknown to us at the time problem with the cooling system, it would immediately start to over heat again as soon as we got back up to speed on the freeway. Once we were home and discovered the problem and fixed it, it would sit all day at 180* and not overheat.

[Baz]

I've had to add coolant twice now in 2 weeks so something's going on with the Silverado......

[Tobra]

Baz, maybe a rotten hose to the overflow tank?

[Baz]

Originally Posted by Tobra

Baz, maybe a rotten hose to the overflow tank?

Thx Tob - will take a look tomorrow. I just haven't seen any leaks so not sure where the coolant is going....