boiling coolant tank and etc

[Spycker]

I was driving to work in my 89' Lebaron 2.5 Turbo all normal. When I got to a stoplight, I noticed a rough idle sound, it goes away when i accelerate but also the temperature gauge needle tried going higher than its middle point but the fan wouldnt let it. I get to my parking spot to check her out and noticed the radiator had half coolant inside, the coolant in the reservoir was boiling a bit. The head gasket is fairly new, previous owner had it done. Theres no white smoke, no coolant in oil, no coolant dripping near anywhere in the engine. In my lunch break, I did a test and had the temperature rise up to the " boiling point " and noticed the needle would go up in the middle then come down, only for it to come right back up after 20 seconds. Could this be a thermostat? also and FYI, my radiator cap is not spring loaded and the radiator still is about a year old. Thanks!

[iTurbo]

I would start with replacing the radiator cap.

[Spycker]

changed the cap, still does the same but no more leak from the cap or boiling coolant

[5DIGITS]

changed the cap, still does the same but no more leak from the cap or boiling coolant

Does the heat work well in the car - good flow through the heater core?
Does the bypass valve function properly and without restriction?

I've seen numerous vehicles where the heater coolant and/or bypass circuit has been omitted.
This is an undesired scenario as the coolant system is designed to have a low-flow path around the thermostat.
Without it or when it becomes blocked/restricted, the coolant system is dead-headed when the thermostat is closed and extreme temperature oscillations can occur much like you describe.

[Spycker]

the heat works well, i havent changed the thermostat since I've gotten the car, bypass valve?

[minigts]

I'd make sure you don't have any air in the line. Fluctuation in the gauge like that usually means air pockets are present. If you have not, I would look at drilling a 1/16 hole in the t-stat and just ensure you bleed the system.

[5DIGITS]

the heat works well, i havent changed the thermostat since I've gotten the car, bypass valve?

Typically located next to the brake booster or behind the battery tray, it looks like this.

[5DIGITS]

I'd make sure you don't have any air in the line.
Fluctuation in the gauge like that usually means air pockets are present.
If you have not, I would look at drilling a 1/16 hole in the t-stat and just ensure you bleed the system.

Good point Jon.
Most thermostats usually have existing provisions to support the air bleeding/burping process.
This can be a very small hole provided by the manufacturer but can also exist as valve to seat clearance around the entire valve circumference and common valve notch provision.
Where manufacturers provide these provisions, some consider it to be beneficial to install the valve so they are at the top for idle speed air purging.
Although, normal/elevated engine RPM coolant flow rates accomplish air pocket movement to where it can be vented through the cap, during normal over-flow bottle operation.

[Spycker]

the picture isnt showing up.

- - - Updated - - -

noticed splashes of oil around the head

[5DIGITS]

The oil leakage and resulting residue seem to be from the VC/cam seal areas and most likely unrelated to the coolant issue.
On the other hand, overheating a thermostat can damage it and if its also old then inspecting/replacing it may be worth while.

[Spycker]

Ive just replaced the radiator cap and now theres that leak again, time for a new radiator?

[Spycker]

Ive replaced the thermostat, thermostat housing, thermostat gasket. Ive also installed a new hose from the radiator filler cap to the reservoir tank. Theres no more leaks anywhere and im still getting bubbles bubbling in the tank and the temperature gauge only moves up then down during idle and street driving but not on the highway

[minigts]

Ok, but does the thermostat have the bleed hole? Did you install the t-stat with the bleed hole at the top? Did you run the heat while filling with water/coolant to ensure there were no air pockets in the system? If all the above has been done and everything checks out, I would suggest getting a block tester and seeing if you're getting combustion gas in the cooling system. The block tester is a liquid that reacts with whatever may be coming from the combustion chamber (short idiot version because I have no idea how exactly it works ). But when you use it, it will mix the fluid with the coolant and if it turns a certain color, it is indicative that there is combustionable gas getting in the cooling system.

This was the case with the IROC I drove cross country. We stopped in Seattle and tested it and sure enough it ended up being loose head bolts.

[tryingbe]

https://www.youtube.com/watch?v=0xcxumccf8Q

Could be just normal with the cap off.