edb150 Posted July 21, 2019 Share Posted July 21, 2019 I changed the stat in my 96 427 today and I feel like a dummy because I forgot about the weep hole. it was 95 plus in Illinois today and I was out in the sun so my brain wasent in top shape. whats it there for and whats gonna happen? im chasing an overtempt issue when the trucks loaded and its over 90 out. first thing I did was replace radiatorbut that dident help. I replaced the t stat, coolant filter , and the bypass valve. condenser and cooler clean of debris. truck pulls a dump trailer so I clean it often. seems to run cooler with new stat but I haven't driven yet now im wondering about the position the weep hole is in. any help would be appreciated Quote Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/ Share on other sites More sharing options...
h67st Posted July 21, 2019 Share Posted July 21, 2019 They say to put it at the top so the air will pass through. Haven't really had experience with one causing trouble from being upside down. Quote Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/#findComment-428409 Share on other sites More sharing options...
theakerstwo Posted July 21, 2019 Share Posted July 21, 2019 Do a water bottle test and also a water pump pressure test.How hot does it get and is the gauge correct? Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/#findComment-428416 Share on other sites More sharing options...
edb150 Posted July 21, 2019 Author Share Posted July 21, 2019 (edited) starts goin into red and have to back off. gauge is correct/ when it gets hot I get black smoke out the pipe. haven't let it overheat. at cold start it was at 195 within 15 to20 min at idlen ow with the new stat its 160 hoping its fixed Edited July 21, 2019 by edb150 Quote Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/#findComment-428417 Share on other sites More sharing options...
Lmackattack Posted July 21, 2019 Share Posted July 21, 2019 did you check the water pump to see if its pushing water? if its moving water and the belts are tight next. pressure test the system to see if you have a bad head gasket pushing air into the coolant? you would see soot and bubbles in the coolant. the weep hole is to allow air to bleed out of the system. it also helps keep the t-stat housing always full of water so that the t-stat will open and close at the correct temps. some t-stats have a small hole drilled in the ring. others may have a check ball. the reality is I have never noticed a car overheat because of the weep hole location. once the T-stat opens it lets out any air and the turbulent water should carry any air out of the housing. Quote Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/#findComment-428418 Share on other sites More sharing options...
JoeH Posted July 21, 2019 Share Posted July 21, 2019 I would take it apart and correct it. Quote Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/#findComment-428421 Share on other sites More sharing options...
JoeH Posted July 21, 2019 Share Posted July 21, 2019 Also you can boil a tstat to make sure it isn't faulty. Quote Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/#findComment-428422 Share on other sites More sharing options...
fjh Posted July 21, 2019 Share Posted July 21, 2019 10 hours ago, edb150 said: starts goin into red and have to back off. gauge is correct/ when it gets hot I get black smoke out the pipe. haven't let it overheat. at cold start it was at 195 within 15 to20 min at idlen ow with the new stat its 160 hoping its fixed Hows your charge air cooler any boost leaks? shouldn't have black smoke under load unless your lugging it! an over fuel /lack of air situation may be causing this issue ! also if you have a viscus fan are you sure its working correctly? Quote Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/#findComment-428430 Share on other sites More sharing options...
edb150 Posted July 21, 2019 Author Share Posted July 21, 2019 (edited) fjk you may be on to something there is some sort of exhaust leak sound like at the back of the motor when its under load. its been there a while but its worse now. If I remember right I had a mack tech tell me about a pipe on the back of the motor. is there a pipe from the manifold to the compressor? Edited July 22, 2019 by edb150 Quote Link to comment https://www.bigmacktrucks.com/topic/58224-thermostat-weep-hole/#findComment-428458 Share on other sites More sharing options...
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