Help me diagnose my expansion tank level woes (1 Viewer)

[Hokie LX]

Hi all,

Finally wanted to figure out my coolant level woes that have been ongoing for the entirety of my ownership. My coolant expansion tank level sits at the very bottom of the drain hose at all times. When I put more coolant in the expansion tank, it gets sucked out and never returns. Been happening the entire time I've owned the truck (50k miles). I've replaced the radiator and T's during my ownership and did a full system flush. Coolant level in the radiator is consistently at the top of the fins and does not change. No evidence of leaks elsewhere in the system. Coolant temps via scanguage are stable in the 185-205 range.

There is evidence of leaking around the radiator cap. It was replaced with a 108KPa cap (PN: 16401-67150) earlier in 2019 but same issue persists where the coolant expansion tank level drains to the bottom of the drain hose but does not replenish.

Is this a sign of the wrong pressure radiator cap? Another issue? FM states between 93-123KPa is standard. Is this a sign of excess pressure in the system?

Thanks

 

[suprarx7nut]

Exactly how much coolant have you lost? The system takes a large amount of coolant and the expansion tank is supposed to lower in level until you've filled the rest of the system. Maybe you've always been low and not filled enough to actually fill it? Checking the radiator level itself is not really valuable. The coolant level should be up to the very, very tip top of the brim of the neck. If the radiator isn't practically overflowing (even when cold) I think you've got too little coolant in the system.

If the coolant level is below the neck, just covering the fins, you're low on coolant.

I'm guessing you've got a slow leak (maybe just at the neck/cap) and you're just witnessing the expansion trying unsuccessfully to keep the system topped up.

Pending the mileage on your truck, a new radiator isn't the worst way to spend preventative maintenance funds. They do crack and fail in the top end tank and it's as much as a wear item as you'll find in the engine bay aside from the filter, spark plugs, heater T's and fluids, IMO.

 

[JunkCrzr89]

Have a leak somewhere. Water pump, crossover pipes, oil cooler, etc are all candidates. When were timing belt and water pump last replaced? See any coolant leakage in front where oil pan mates to block or above? Also could have damaged gaskets/upper extension of rear crossover pipe when you changed heater Ts.

 

[Hokie LX]

Exactly how much coolant have you lost? The system takes a large amount of coolant and the expansion tank is supposed to lower in level until you've filled the rest of the system. Maybe you've always been low and not filled enough to actually fill it? Checking the radiator level itself is not really valuable. The coolant level should be up to the very, very tip top of the brim of the neck. If the radiator isn't practically overflowing (even when cold) I think you've got too little coolant in the system.

If the coolant level is below the neck, just covering the fins, you're low on coolant.

I'm guessing you've got a slow leak (maybe just at the neck/cap) and you're just witnessing the expansion trying unsuccessfully to keep the system topped up.

Pending the mileage on your truck, a new radiator isn't the worst way to spend preventative maintenance funds. They do crack and fail in the top end tank and it's as much as a wear item as you'll find in the engine bay aside from the filter, spark plugs, heater T's and fluids, IMO.

Thanks. Truck has ~215k on it now. Rad, TB, and all related accessories are only 30k miles old (2 years).

I haven’t lost coolant continuously. I poured another inch or two of coolant in the expansion tank ~4 months ago to see if it would disappear and it did. Now the level in the expansion tank and in the radiator do not move. It's been months and the level doesn't go down at all. It's as if the coolant leaks out until the level in the expansion tank is at the drain hose and then it stops leaking...maybe you’re right and I never had enough in the rad so it kept taking it from the expansion tank. I’ll try filling the rad to the brim and see if it still drops in the expansion tank.

 

[suprarx7nut]

Thanks. Truck has ~215k on it now. Rad, TB, and all related accessories are only 30k miles old (2 years).

I haven’t lost coolant continuously. I poured another inch or two of coolant in the expansion tank ~4 months ago to see if it would disappear and it did. Now the level in the expansion tank and in the radiator do not move. It's been months and the level doesn't go down at all. It's as if the coolant leaks out until the level in the expansion tank is at the drain hose and then it stops leaking...maybe you’re right and I never had enough in the rad so it kept taking it from the expansion tank. I’ll try filling the rad to the brim and see if it still drops in the expansion tank.

My suggestion: Fill the rad completely up to the brim of the neck. Fill the expansion tank to the high mark on the bottle or just above it. Observe over a few weeks as you drive. The system contains over 4 gallons of liquid. You could top up an inch or two many, many times before filling a fraction of the system. Last time I drained coolant on mine I think it took two pretty complete fills of the expansion tank before it stopped pulling liquid from the tank.

When you're freshly filling the system the intention is that you'll have unavoidable bubbles in the system. As the bubbles work themselves out, they will be replaced with liquid from the expansion tank (if it's topped up). It's plenty possible you just had a gallon of air space when the coolant was last topped up and you've been very slowly replenishing it at the expansion tank.

Hard to say without knowing how much you're going through, though. It sounds like you haven't poured more than a gallon into the overflow so I suspect you might just need more coolant.

If you have been adding that much coolant, time to inspect for leaks at all the connections. A pressure tester cap adapter tool might help.

 

[KFunk740]

I don't understand what you guys are doing here. The expansion tank is supposed to be filled up to the full line, why would you never not fill it up to that after making sure the radiator is full? It's right there in the factory service manual, and the same as every other car I've had. Not up to to the top of the expansion tank, and not to the bottom. Just the high mark line. It provides a buffer for expansion and contraction, and a little insurance in case you lose some.

 

[abuck99]

^ Reservoir filled to the full line - HOT.

When cold the fluid level should be between the Low & Full marks. Ideally, check level in cold state first thing in the morning; after 8+ hrs of sitting (overnight). Add enough fluid to be half way between the Low & Full marks and take a sharpie and make a line there. Monitor your fluid level first thing in the morning for a week or two and see if its dropped below the line. Keep in mind different ambient temperatures will affect fluid level slightly. If you're adding coolant every day or even once a week you've got a leak somewhere: check your evaporator-core, lines going to & from oil filter cooler, T's, cross overs, intake (there's a cap that can pop out and start leaking). Look for the dried coolant build up.

The radiator cap you want reads 108kPa on it and the superseded part# is: 16401-67150 .

 

[KFunk740]

http://www.dustbird.com/ih8mud/FSM/Cooling.pdf

Nothing in the FSM about it being only to the full line when 'HOT' and nothing mentioning anything about setting at only 'half way.'
For finishing the bleeding procedure, it says to
"(d) Stop the engine, and wait until the engine coolant cools
down.
(e) Refill coolant into the reservoir until it is ”FULL”.""

I think you're misinterpreting the first page where it says. "The engine coolant level should be between the ”LOW” and ”FULL” lines at normal temperature
(20°C(68°F))."
Yeah, it should be between there normally, or you got real problems. But for starting it out baseline after a bleeding, it should be all the way to Full when the engine is cooled off. Why do you think there's a ton of space over the Full line? That's room for it to expand when it is really HOT.

 

[Hokie LX]

Filled it up to the brim in the rad and full line in the expansion tank this morning before heading to work. I filled it to the FULL line cold as the extra space in the tank will capture the additional fluid fed into the tank once hot. I'll monitor it over the next few days/weeks to see if it moves.

Like I said previously, the level never changed after sucking the extra out of the expansion tank so I'm thinking @suprarx7nut was right in that I just never filled it up to the tippy top when I replaced my rad. Truck has been on long road trips, towed trailers, etc in the high heat with no issues or change in fluid level so I'm thinking this is the case. Time will tell.

 

[suprarx7nut]

Filled it up to the brim in the rad and full line in the expansion tank this morning before heading to work. I filled it to the FULL line cold as the extra space in the tank will capture the additional fluid fed into the tank once hot. I'll monitor it over the next few days/weeks to see if it moves.

Like I said previously, the level never changed after sucking the extra out of the expansion tank so I'm thinking @suprarx7nut was right in that I just never filled it up to the tippy top when I replaced my rad. Truck has been on long road trips, towed trailers, etc in the high heat with no issues or change in fluid level so I'm thinking this is the case. Time will tell.

I've had a few other Toyotas with similar cooling systems and the 100 has an unusually large volume in the cooling system in every aspect. The capacity is huge. The overflow bottle is huge. You can run low for quite a while without any harm. My fingers are crossed that you just need a little more fluid.

Let us know how it turns out!

 

[abuck99]

http://www.dustbird.com/ih8mud/FSM/Cooling.pdf

Nothing in the FSM about it being only to the full line when 'HOT' and nothing mentioning anything about setting at only 'half way.'
For finishing the bleeding procedure, it says to
"(d) Stop the engine, and wait until the engine coolant cools
down.
(e) Refill coolant into the reservoir until it is ”FULL”.""

I think you're misinterpreting the first page where it says. "The engine coolant level should be between the ”LOW” and ”FULL” lines at normal temperature
(20°C(68°F))."
Yeah, it should be between there normally, or you got real problems. But for starting it out baseline after a bleeding, it should be all the way to Full when the engine is cooled off. Why do you think there's a ton of space over the Full line? That's room for it to expand when it is really HOT.

Not misinterpreting FSM because I’m not following its instruction, just using common sense. I prefer my coolant tank to be spot on the full mark when hot. The sharpie halfway mark is a visual reference to monitor level over time- thats all.

If filled to full when cold, then it’s going to be overfull when hot (if the cooling system was correctly burped after flush or rad replacement) Not a big deal either way.