ClubSiRacer

It seems that since I raised my redline to 8900rpm, my coolant levels tend to fluxuate some. I will fill the radiator so their are no bubbles and then run the car for a day, sometimes to redline, and the next day some of the coolant has spewed out the edges of the radiator cap (rather than going into the overflow tank) and the radiator hose is down a few ounces of coolant.

I pulled the cap off today and started the car while it was cool. No bubbles came up but when I rev the motor the coolant level rose slightly and then dropped again when revs dropped. I'm guessing that is from the pressure being built up by the water pump. Again, it doesnt have any signs of oil in the coolant and no bubbles come up when its running. It also doesnt smoke, even on startup or hard acceleration. Nor are their any leaks anywhere else on the motor that I can see. It doesnt steam or smoke anywhere when the motor is hot.

The only thing I can think of is that the radiator cap is bad and isnt causing the coolant to overflow into the overflow tank (and back into the radiator after it cools back off). Stranger yet, I left the coolant level where it was this morning (a few ounces lower than full) but without any bubbles in the system and closed the cap and let the car idle to 180° and the coolant lines puffed up with coolant like normal. And thanks to the poor design of the coolant system on the 99-00 Si's, the coolant bleed valve is on the back of the water pump where it is damn near impossable to get to. I'm fairly sure their is no air in the system as the upper coolant line "sucks in" just a tad when it cools back off since it cannot take coolant back in from the overflow tank which is at a normal level all the time.

Thought?

ClubSiRacer

I cant be the first person to have this problem before... Perhaps its just a bad radiator cap? Then again, I tried another used cap I had around and it does the same thing.

ClubSiRacer

Ok I examined the caps and both look fine but I have no means of testing them. Should I just plunk a few bucks down and get another brand new cap and hope it doesnt do the same thing? Or could something else be the matter here?

ClubSiRacer

Looks like i'm holding a conversation with myself... How interesting.

Anyhow, I found the culprit... It turns out the line from the radiator to the overflow tank was clogged up right at the plastic 90° bend in the cap. It wouldnt let ANYTHING go by it until I cleared up that problem.

DeepSi

glad you found the problem