Coolant Overflow Tank-Overflow

[Spector]

A year ago I had a sensor replaced (engine light was on) and ever since the overflow tank has to be kept at the low level when cold. Anything higher and it overflows when hot. Prior to the sensor (manifold pressure sensor) replacement the tank cold be kept at a higher level with no problem. Anyway, it runs fine so I let it be but yesterday hit the foliage scene on the mountain and after returning home and after engine cooled the tank was sucked completely dry. there is no leak etc, it definitely overflows.

So, could this a radiator cap issue that has grown weak over the years or ?? Hate to bring it back (one dealer left in the area) but it never occurred prior to the sensor replacement.

Any thoughts as to what is happening?
1997 Mitsubishi 3000 GT VR4 38,000 miles

 

[Colt45ws]

Might be a radiator cap issue, yes. I do not see how a sensor could affect this.

 

[Boomer]

Also might be the signs of a cracked head/block or a bad head gasket.

 

[Colt45ws]

Ah, yeah, thats true.

 

[aquariuscsm]

Is this happening on your VR4? If it`s not running abnormally hot,my vote goes to a radiator cap issue as well. I`m curious,what oil/filter combo do you run?

 

[Spector]

Amsoil 10W30 with a K&N oil filter and OEM air filter

Almost positive not a head gasket or leak issue, I have observed the overflow several times in the past month, Either a cap or something causing too much pressure.

 

[rpn453]

I'd change the rad cap.

 

[mechtech2]

If it boiled over into the puke tank, I'd say head gasket or head.
But it was going up and down on a regular basis, with no normal loss.
So it seems your radiator cap is not at full rated pressure.
I'd get a new one.

 

[Chris142]

Check the neck on the radiator where the cap seats. Make sure that it's smooth.