2G Help! Coolant reservoir filling up

[MonWill85]

I’m restoring my 97 Mitsubishi Eclipse turbocharged.

I’m having issues with my coolant reservoir filling up past the full mark on the bottle. I’ve changed the water pump, timing belt, upper and lower hoses, the radiator cap and the thermostat and I’m still having these issues. I’ve taken it to two different mechanics and still the same issue

I took it too autozone because the check engine light and I had several codes popping up P1105, P0505, and P0141 and P0135 which are my O2 sensors but I’ve replaced these last year. I’ve passed smog

When i accelerate the car begins to stutter and when that happens my coolant reservoir begins to overflow. Does anyone have the answers as to why this is happening. I NEED HELP!!!!

 

[pauleyman]

You should perform compression and leakdown tests. What you're describing is head gasket related. You won't know for sure without testing.

 

[MonWill85]

The first mechanic said that he did a pressure test and everything came out fine. When the car sits and idles it sounds strong. I’m still running into the same issues

 

[CKOPOCT]

Only reason is the combustion is pushing past the head gasket (or a crack in the head/block) and pushing gas into the water passages. That added pressure is causing the coolant to overflow.

 

[MonWill85]

The first mechanic when he changed my water pump, timing belt, upper and lower hoses said that he did a pressure test and the results were 160 all around plus the car is not overheating which is the confusing part

 

[miliman13]

so what exactly is the issue ? Your reservoir is overfilling ? That’s it . Or are you loosing coolant and spilling it out of the container and you are not overheating so what is the issue ??

 

[MonWill85]

My reservoir is overfilling and when I level it out it drives good. Ex. Today me and my wife are heading home and the car starts to hesitate/studder as I’m accelerating, I get out and check under the hood and the coolant reservoir is more than 3/4 full.

 

[miliman13]

My reservoir is overfilling and when I level it out it drives good. Ex. Today me and my wife are heading home and the car starts to hesitate/studder as I’m accelerating, I get out and check under the hood and the coolant reservoir is more than 3/4 full.

Your studdering has nothing to do with your coolant reservoir. You possibly have bad vac lines or your leaking boost . Perform a boost leak test. And clear your code to see what actual cells you still have.

Your reservoir is not a constant , the fluid will raise and lower with driving/ use and temp.

Perhaps you’re making connections based on your observations that are not dependent on one another.

 

[CKOPOCT]

When your car heats up, the pressure inside the cooling system (water jackets) builds as the coolant gets hot and tries to expand. That pressure helps to keep the coolant from boiling. When the pressure reaches the pressure rating of the radiator cap, the top valve in the cap opens and allows the excess pressure (and therefore coolant) to bleed off and into the overflow bottle. When yoy shut the car off and let it cool down, the pressure drops and the system goes into a vacuum, sucking the coolant back out of the bottle and into the water jackets. This is how the system stays full, and is the purpose of the overflow/reservoir bottle. It's also why you have to check the bottle and periodically add coolant (the water evaporates and leaves the antifreeze behind).

If you have a bad radiator cap - it isn't sealing properly - it can fail so it doesn't build pressure. The result will be coolant passing into the overflow bottle under throttle and any time the system begins to build pressure. It likely will also not suck the coolant back into the pipes (no seal with which to form a vacuum). Consider taki g the car to your local Autobone or other parts dtore and have them test the cap. If it doesn't hold pressure properly, replace the cap and see if that resolves your problem. You can also visually inspect the cap and the lip where it sits to see if you notice an obvious problem with the seal (gouged seal/lip, bent cap, debris getting in the way, etc.).

 

[MonWill85]

Thank you. I replaced the radiator cap and the thermostat the day before yesterday

 

[CKOPOCT]

Sorry. I read that in your first post but completely forgot. You said a mechanic did a compression test and came up with 160 across the board. 160 for the 4g63 isn't bad, but it is a little low. As @pauleyman said, you should perform a proper compression AND leakdown test on your engine. Do it yourself - don't take it to anyone else. Reason is you need to report the specific numbers and findings to us. I've done compression tests on dozens of vehicles and have never had the same numbers across all cylinders. You need to know what the tests tell you. Here's a link on how to do the tests yourself:

Thread 'Compression and Leak-Down Testing' https://www.dsmtuners.com/threads/compression-and-leak-down-testing.338152/

The tests aren't difficult or highly technical. Let us know what you find out so we can help you get to the bottom of this.

 

[MonWill85]

Thank you. I’ll get to it as soon as I can. Also in the process of moving.

 

[CKOPOCT]

Ugh... I feel your pain. What is your mechanical ability? Oil changes flummox you? You rebuild engines in your sleep? Knowing this will help us tailor our answers to your abilities. Don't want to talk down to you, or talk over your head. Neither is helpful.

 

[MonWill85]

If the work is simple and easy to get to I’ll usually fix it myself.


I’ve replaced thermostat,
radiator cap
O2 sensors,
lower and upper control arms on both passenger and driver side.
ignition coils
Map sensor
Camshaft sensor
Spark plugs

The work I’ve had done to it is

Water pump/timing belt
Starter
Fuel pump

Again of it’s easy and I’m able to access it. I’ll change it myself.

 

[pauleyman]

You might also consider a coolant pressure check. If pressure diesnt maintain your would need to find out why.

 

[MonWill85]

Thanks. The mechanic said that he did a pressure test before he installed the new timing belt and water pump but I’ll do my own pressure test when I get some time

 

[DSMPT]

Just in case, aren't you using tap water with a cheap aftermarket aluminum radiator?

It's kinda common but not often mentioned. And maybe this is not your case in this time, but this can be a cause of mysterious overheating issue.
In case if you are using tap water especially with a cheap aluminum radiator, there is a chance that you have coolant electrolysis which causes gas and pressurizes the system. So even if all the engine cooling system components and the head gasket are working good with zero leak, the coolant is always pushed from the system to the reservoir and overflowing from there, then the engine gets overheated.
If you feel some pressure in the upper radiator hose in the morning or after the engine gets cold, or check the voltage in the coolant then if you see 0.4~0.5V or above, you may have this issue.

 

[MonWill85]

No I am not using tap water. I’m using a 50/50 mixture that I’ve purchased from autozone. When the car is cold there is no pressure in the hoses. When the car is warm and I have driven it for a few minutes there is pressure in the hoses.