When recently doing a flush and fill of coolant. I ran into a issue where the coolant is going straight to the overflow tank until it starts to overflow. Did I just add too much coolant? I have a brand new Pettit AST and all hoses were changed and air tight.

 

First off, make sure the overflow tank isn't too full. It has a dipstick, you want it in the middle of the range on the dipstick. If it's too full it will constantly barf coolant.

Think about the way it works - the engine heats up the coolant and the coolant expands. Extra coolant gets pushed past the radiator cap and into the overflow tank. Once things cool back down, the system cools and compresses, and then sucks that extra coolant back from the overflow tank.

If the line from the AST nipple to the overflow tank has a hole (even a small hole) it can't suck the coolant back it, it just sucks air through the hole. Also if the tank is filled to the top the extra coolant just barfs out of the tank instead of having room to store it in the tank.

You could also still have air bubbles in the coolant system which is causing some localized overheating. Have you used a Lisle funnel to fill the system and get air out?

Dale

 

I did use a lisle funnel but as I continued to fill and burp air coolant starts to come out of the little hole beside the overflow coolant neck. When starting the car it starts to overflow even more and then the add coolant sign comes on when the coolant stops coming out.

 

Did you have the funnel on the AST or the thermostat housing? The funnel needs to be on wherever the overflow nipple is attached since you don't want the coolant you are adding with the funnel to go into the overflow.

Dale

 

Ah I see, I was filling from the thermostat housing because I read that I should always fill from there but if I fill from the AST how will the thermostat get full?

 

Coolant must be getting past the AST cap in order to flow to the overflow tank. The AST cap should be a pressure relief type cap that lets coolant flow to the overflow tank only when the coolant pressure gets too high (i.e., overheats). Also, I think Pettit supplies a pressure relief cap for its AST that has a pressure relief lever. By any chance do you have the wrong cap on the AST, or the relief lever in the wrong position?

 

The whole system is connected, it will all fill up. You may just need to remove the cap on the thermostat housing at some point to make sure there's not trapped air up there.

I haven't filled a system with an AST in a million years, though .

Dale

 

I have an AST. Always fill mine from thermostat housing. As retserof said, the coolant will fill the system since the cap on the AST should have it closed off (cold).

Starting fresh with empty system, fill overflow, fill AST to top, put cap on, fill system from thermostat housing.

 

I tried doing this yet still the same issue. The coolant goes straight to the overflow tank which then begins to overflow out the bleed hole and the add coolant sensor goes on. Have any other ideas on what my issue might be ?

 

I would try a new pressure cap on the AST even though you say its a new unit. It should not be letting coolant flow to the overflow without being pressurized.

 

With an AST setup you typically have a flat radiator cap with no spring plunger on the fill neck (thermostat housing) and a radiator cap with the spring and plunger on the AST. If they are swapped the car will shove coolant into the overflow tank as fast as it can.

Sometimes people have 2 radiator caps and no flat cap, which is fine. The big thing is not having the flat cap on the AST.

Dale

 

The stock cooling system has 2 “radiator” caps, although neither one is actually on the radiator: the "flat" filler cap is on the thermostat/water pump housing on the engine, and the pressure relief cap is on the top of the AST tank. If those caps are correctly installed and the pressure relief cap is working properly, the only other explanation for your problem is that your AST hoses are hooked up wrong.

The stock AST has 3 hoses attached to it. From top to bottom: First hose runs from the pressure relief cap neck of the AST to the coolant reservoir tank located below the right headlight. Second hose runs from the side or middle of the AST tank to the filler cap neck on the thermostat/water pump housing on the engine. Third hose comes off the bottom of the AST tank and goes to the bottom of the radiator. The Pettit AST tank hoses connect the same way.

If your AST hoses are correctly plumbed, you should replace the AST pressure relief cap, as AE Racer suggested. The stock one looks like this:




The stock "flat" cap that goes on the thermostat/water pump housing looks like this:



NOTE: the 2 caps actually are the same size (my stolen photos are not to the same scale).