Pressure in the cooling system?
 

Buddy has a 85 with a 13b 4 port and he called me because his cooling system is presurizing and going past the cap in to the overflow tank. When he runs it with the cap off he has bubbles coming up the the top continously. I think it could be a inner water o-ring giving way, but he has clean exhaust....it does idle rough at stop lights.
Any clues?

as you said, it's probably a blown water seal. check the coolant for combustion gases, but i'd put 5 :D on it ...

anouther way to test is to wipe your finger on the tail pipe and taste it.

this is a old school trick, and not very health, but if it tastes sweet, your burning coolant.

Start simple.. change the rad cap first, then if that doesn't work, get a cooling system pressure test done..

Thanks guy's for the input, I'll pass it on and report back on the results.

Depending on how well he kept up with his car, it is possible to have a bad thermostat that has locked shut or partly open, but like Partsguy said...start simple these are things that really need replacing by this time anyways and will help with cooling after the problem is resolved. I would change the radiator cap along with a new thermostat both items will cost you about $30 in total. Go to the dealer for the thermostat. I had a 90 GXL that blew a water seal and blew a split in the top radiator hose caused by the pressure build up. If it has constant bubbles coming from it with the cap off I would say that the seal is shot and letting compression in the water jacket. If you pull the spark plug thinking you might see some water if the seal is blown this will not work due to the fact the water is turning to steam and burning off. Which is why 82streetracer was saying to taste the tail pipe, I would just go back there and take a breath and see if you smell coolant, it will smell sweet ;] Good luck.

Mike

another cause of this would be a corroded rotor housing from running straight water I've seen this many times back in the early 80's on engines I was building

hi pressure coolant
 

Sounds like the exact problem I had,but I have a 3rd gen,more than likely it is your cooling seals,but make sure your fan is working,thermostat's good,are you getting heat,do a pressure test,its not your cap trust me.

thanks for sharing but with input it is good to check the date on old threads...... this one is from 05

A newbie with an FD, that has engine issues. There's a rare find........

nevermind... wow old thread...