Perplexing Situation - Intake Manifold Gaskets Replacement

[99xlsdude]

Today I replaced the upper intake manifold gaskets on my 99 XLS (V6 OHV 109K miles) to repair P0171 and P0174 codes. I put the truck back together and started the engine without any problems. However, after about 3 minutes anti-freeze started running from the radiator cap - this has never happened before. Thinking it was just a coincidence (not related to changing the manifold gaskets) I replaced the radiator cap. However, the same thing happened again when I restarted the engine.

OK - so now I became suspicious that the anti-freeze leaking from the radiator cap was somehow related to changing the gaskets. So I rechecked my assembly and found that I forgot to connect the hose that runs from the air intake tube (after MAF and before TB) to the oil filler pipe. So, I connected the hose and restarted the engine - the leaking stopped!!! I restarted several times (hot/cold cycle) and went on a test drive and no more leaking.

I am perplexed!!!! How is it possible that there is a connection between anti-freeze coming from the radiator cap and this hose being disconnected? Reconnecting the hose appears to have to fixed the problem but I am concerned that something else might be going on. Any ideas?

 

[BIGHVM]

Hmm, got me there mate- have no ideas!

 

[99xlsdude]

It's been 3 days (75 miles of short trips) and there have been no coolant leaks from the radiator cap since I re-connected the hose. Truck is running great. It would be nice to know why this happened but I guess a little mystery keeps life interesting.