LLY: Won't get to temp then suddenly Overheats?

[dirtymax36]

Last week i just sent my lly in for a new water pump, and before i sent it in it was just fine on temperature. I have studded heads and grade c gaskets as of november this year. Within the past 2 days i was just cruising along about 55 and i watched my temp guage go from 210 to 240 just like a snap of fingers. My gauge face is correct also because I data logged it in efi. The drivers side pipe started to suck shut so i got a brand new gm cap and that solved my pipe problem but on some days I'm getting a lot of pressure in the tank, and some days there's no pressure at all but will still over heat. It will stick on 170* for forever and not warm up even if egts get over 1250. Then suddenly it will pop open to 235 or so. What could this be? Any help would be appreciated as this has me confused.

 

[DURAJETLLY]

Have you tried swapping Thermostats?

 

[dirtymax36]

I ordered new Mishmotos but they haven't got here. Thermostats or head gaskets are all I could think of

 

[DURAJETLLY]

Guess you can always do the check after it sits overnight and squeeze the upper rad hose and see if its hard.

 

[dirtymax36]

Upper radiator hose is soft over night

 

[DURAJETLLY]

I'd do your thermostats and see where that lands you.

 

[ALLY Fox]

Sounds like air in the cooling system. Before you change t'stats, try purging air out of the system. There should be a bleed plug near the t'stats. Also, do some clicky....
http://www.dieselplace.com/forum/63...ngine/289926-bleeding-air-cooling-system.html

 

[gassux]

air in the system, open the bleeder. It might take a week or so to get all the air out

 

[dirtymax36]

I bled the system twice until it was straight fluid and no air bubbles, I left the bleeder open over night while the fluid level wasn't running over the top and it still did it today. It's making a sound as if there's pressurized air in the radiator almost

 

[dirtymax36]

Update for the night: new thermostats in and it still over heats. a very reputable diesel shop mechanic stopped by to help me tonight and we noticed the heater core FEED line was hot, while the heater core RETURN was stone cold. The heat inside the cab will NOT work and the air is just cold. Could there be a blockage in my heater core not letting the coolant fully circulate in the radiator and cool off? We made sure there was no air in the system either. after it has been shut off there is a little air in the overflow tank for pressure but there has been no fluids coming out of the tank. Any more thoughts? thanks for the reply

 

[PACougar]

Update for the night: new thermostats in and it still over heats. a very reputable diesel shop mechanic stopped by to help me tonight and we noticed the heater core FEED line was hot, while the heater core RETURN was stone cold. The heat inside the cab will NOT work and the air is just cold. Could there be a blockage in my heater core not letting the coolant fully circulate in the radiator and cool off? We made sure there was no air in the system either. after it has been shut off there is a little air in the overflow tank for pressure but there has been no fluids coming out of the tank. Any more thoughts? thanks for the reply

Replace your heater core. They can absolutely get blocked.

 

[whytry85]

you may try to back flush the heater core too if all else fails... had a gasser plug up one time and did the same thing. backflush fixed it... good luck man.

 

[ALLY Fox]

Are you using Dexcool? There have been problems with Dex not mixing well with some other coolant brands. Dex is good stuff but mixing with other brands has been known to cause coagulation and plugging. If you change from Dex to another coolant, it is important to flush thoroughly otherwise you can create major problems.