88pioneer Posted August 3, 2009 Share Posted August 3, 2009 I can't seem to find the radiator cap on my 88. I don't know if its just not there or if i'm completely blind, but i can't find it. If anyone can help me with this i would really appreciate it. Link to comment Share on other sites More sharing options...
Eagle Posted August 3, 2009 Share Posted August 3, 2009 It's the cap on the plastic bottle back by the firewall, on the passenger side. Common misunderstanding. That bottle is not a typical overflow recovery bottle. On the 87 - 90 XJ and MJ 4.0L engines that bottle is part of the pressurized cooling system. Do not EVER try to loosen that cap when the system is hot. Don't fill the bottle to the top. "Full" is to the halfway mark when cold. The air space allows for coolant expansion. Link to comment Share on other sites More sharing options...
ComancheKid45 Posted August 3, 2009 Share Posted August 3, 2009 The Renix motors are a closed Cooling system, the Radiator cap doubles as the coolant resevior cap back at the top left of the engine bay. :thumbsup: Link to comment Share on other sites More sharing options...
88pioneer Posted August 3, 2009 Author Share Posted August 3, 2009 oh alright, on my xj thats just the overflow, well thats another mystery solved. Thanks alot Link to comment Share on other sites More sharing options...
Eagle Posted August 3, 2009 Share Posted August 3, 2009 What year is your XJ? Link to comment Share on other sites More sharing options...
88pioneer Posted August 3, 2009 Author Share Posted August 3, 2009 Its a 2000, its on its way out though once the mj is done Link to comment Share on other sites More sharing options...
Lenard Posted August 4, 2009 Share Posted August 4, 2009 Do not EVER try to loosen that cap when the system is hot.. why? Link to comment Share on other sites More sharing options...
Eagle Posted August 4, 2009 Share Posted August 4, 2009 Do not EVER try to loosen that cap when the system is hot.. why? Because it is under pressure and the result will be just like taking the radiator cap off a conventional radiator when it's hot -- the boiling liquid will spew out in all directions and you'll very likely end up with some serious scalding at least on your hands, and possibly on your face and upper body. But don't take my word for it ... go ahead and try it. Link to comment Share on other sites More sharing options...
DirtyComanche Posted August 4, 2009 Share Posted August 4, 2009 Do not EVER try to loosen that cap when the system is hot.. why? Because it is under pressure and the result will be just like taking the radiator cap off a conventional radiator when it's hot -- the boiling liquid will spew out in all directions and you'll very likely end up with some serious scalding at least on your hands, and possibly on your face and upper body. But don't take my word for it ... go ahead and try it. Doesn't it have a warning label somewhere? Or maybe the only warning label is the one warning that the oil filter threads are metric... Link to comment Share on other sites More sharing options...
Lenard Posted August 4, 2009 Share Posted August 4, 2009 Do not EVER try to loosen that cap when the system is hot.. why? Because it is under pressure and the result will be just like taking the radiator cap off a conventional radiator when it's hot -- the boiling liquid will spew out in all directions and you'll very likely end up with some serious scalding at least on your hands, and possibly on your face and upper body. But don't take my word for it ... go ahead and try it. i knew that. i thought maybe it had something to do with it being closed system and didn't want air into it. Link to comment Share on other sites More sharing options...
Eagle Posted August 4, 2009 Share Posted August 4, 2009 Do not EVER try to loosen that cap when the system is hot.. why? Because it is under pressure and the result will be just like taking the radiator cap off a conventional radiator when it's hot -- the boiling liquid will spew out in all directions and you'll very likely end up with some serious scalding at least on your hands, and possibly on your face and upper body. But don't take my word for it ... go ahead and try it. i knew that. i thought maybe it had something to do with it being closed system and didn't want air into it. Just the opposite. Since there is nowhere for "excess" coolant to go when it expands due to heat, there HAS to be air in the system to provide for expansion. Air compresses ... liquids do not. If you fill the plastic tank full and bleed all air out of the system, the plastic tank will explode (or rupture). Link to comment Share on other sites More sharing options...
MiNi Beast Posted August 4, 2009 Share Posted August 4, 2009 Do not EVER try to loosen that cap when the system is hot.. why? Because it is under pressure and the result will be just like taking the radiator cap off a conventional radiator when it's hot -- the boiling liquid will spew out in all directions and you'll very likely end up with some serious scalding at least on your hands, and possibly on your face and upper body. But don't take my word for it ... go ahead and try it. i knew that. i thought maybe it had something to do with it being closed system and didn't want air into it. Just the opposite. Since there is nowhere for "excess" coolant to go when it expands due to heat, there HAS to be air in the system to provide for expansion. Air compresses ... liquids do not. If you fill the plastic tank full and bleed all air out of the system, the plastic tank will explode (or rupture). This is true, I found out somehow one time. :rotfl2: Link to comment Share on other sites More sharing options...
landlubber Posted August 8, 2009 Share Posted August 8, 2009 i've tried opening the cap when my MJ was hot and kinda figured out that it was pressurized because the reservoir tank was bloated and it was hissing when i was unscrewing it. It is possible to remove, however not recommended. there was hardly any fluid in it, that probably made a difference also. Link to comment Share on other sites More sharing options...
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