Second opinion needed on a possible thermostat issue

[DVolk]

Hey , my 92 gen 1 engine , I used to do a 4309234 in a 98 V10 truck . All was well up to a few weeks ago . The temp gauge would raise and drop like normal when the thermostat would open it has ran fine for a year like clockwork . A few weeks ago with the livestock trailer on it . We stopped to get a burger and it was pushing coolant out of the over flow bottle . It acted fine never got hot . Got home topped off the coolant and replaced the cap on case it was messed up .Drove it empty on a 200 mile trip or so . On the way home it was cold around 29 degrees . Next day checked the coolant it pushed coolant out again the bottle was full and radiator down as the first time . It has a new All aluminum radiator , when I put the engine in I put a new thermostat from cummins . For some reason I forget I had to pull the water neck off I can't remember before I ran the engine after install the I don't gasket was messed up so I didn't use that one I got one from Napa . The oil is clean like normal it's a quart low because the deal is leaking in the front because I had to pull the pump off ,about 6 months ago . And I pulled the cover . No steam out of the exhaust . I checked the radaitor with it running its a little low it lowers when under a little throttle then raises at idle . I think the thermostat is bad what are your thoughts ?

 

[BigPapa]

I would suggest a new radiator cap first. Much cheaper and easier to replace. If it's bad it will allow coolant out into the reservoir.

-Scott

 

[JR]

The stat is easy enough to test in a pan of water on the stove if you have doubts about it. Cummins stats are generally pretty reliable, unless you have put a ton of miles on it in a year i wouldn't think it would be bad but is definitely possible.

If you have access to a coolant pressure tester that would be a good bet. May have a leak preventing the system from maintaining proper pressure and consequently boiling over.

 

[NIsaacs]

I would suggest a new radiator cap first. Much cheaper and easier to replace. If it's bad it will allow coolant out into the reservoir.

-Scott

OP said he replaced the cap but didn't say it was new.

DVolk, did you use a new cap and if so what psi rating? I know you are not a newbie to trucks/engines, but are you getting the cap on all the way? The first half is easy, the second half you gotta get serious. I even hate posting this...but...I gotta ask

 

[DVolk]

OP said he replaced the cap but didn't say it was new.

DVolk, did you use a new cap and if so what psi rating? I know you are not a newbie to trucks/engines, but are you getting the cap on all the way? The first half is easy, the second half you gotta get serious. I even hate posting this...but...I gotta ask

That was my first thought was the cap . As when I got the new radiator I didn't like the new cap so I replaced that one with the new V10 one that I had , I did buy a new cap at Napa a 16 lb I believe whatever OEM calls for . I'm fairly sure the cap is on all the way . I do have pressure tester I have not tried that test yet the new thermostat will be here tomorrow afternoon . I don't notice any water leaks unless it's a heater core I know it's not on common for hoses to contact in cold weather .