xjcherokeexj

i have a 1990 jeep cherokee 4.0 with 155k miles on it and the coolant will over flow out of the coolant reservior if i ever mash on it or if i even just drive it for a while. if i keep the cap tight none of the coolant will leak out but if i open it when the reservior is full damn near a gallon of coolant will pour out. it starts to fill up the reservior at about 200 deg. but it i let it sit with the engine off for 5 or 10 minuts then all the coolant will drian back. i've replaced the thermostat, replaced the water pump a few months ago made sure the radiator has no clogs checked almost the entire colant system for clogs and replaced every hose going to the reservior. and the problem still remians. and it still occurs even though im currently running it without a thermostat. any thoughts or suggestions please?

builtnotbought89'

Put your t-stat back in, its there to stop flow of coolant in the radiatorc, so it has time to cool! Also make sure its burped, & not over filled... it should hold right around 210* without ever filling the res. more than half way!

builtnotbought89'

Oh & Welcome to CF!

xjcherokeexj

thanks, i know that the thermostat needs to be there i was seeing if that changed the problem. and how do you burp the cooling system?

builtnotbought89'

Park the back of the jeep on a hill. With the engine running, pull the vacuum sensor on the back of the block, by the fire wall (its in line with the injectors, its copper, 8-10mm head, & has a little vacuum hose coming off of it), once you've unscrewed that sensor you should feel steam/hot air coming out of the hole. Have someone else make sure the overflow stays filled. As soon as coolant comes out of that sensor hole stuff the sensor back in there to plug it! Caution this is very hot! Wear gloves!

xjcherokeexj

thanks man you really know your stuff. i'll do it next chance i get.

builtnotbought89'

I'm here to help! Let us know how it goes!