bypass

[TSham]

Is there a thermostat by pass on the 2007 5. 9 diesel?

 

[JWadford]

Is there a thermostat by pass on the 2007 5. 9 diesel?

???

 

[rbattelle]

I'm not sure whether you're talking about a manual bypass or automatic bypass, but the service manual makes no mention of any bypass. There is a spring-loaded backflow valve that allows the engine to communicate with the overflow reservoir when the thermostat is closed.



Having said that, while reading the service manual section on the thermostat I learned a couple interesting things.



First, the manual says not to use the block heater with ambient temperature above 40°F. I've always wondered where I came up with the idea of plugging in below 40°F - now I know.



Second, apparently if you run the vehicle with no thermostat the engine can overheat because it puts the system in radiator bypass mode. I find that very interesting - does anyone know how it works? I would've expected that without any thermostat the coolant would circulate unimpeded through the radiator and block.



Ryan

 

[brods]

If the 07 5. 9 is the same as an 05, then yes. The 05 FSM shows a bypass that is opened and closed by the thermostat. Assuming we are talking about the cooling system.





Ryan, the 05 manual shows a picture of the flow through the block and has separate pictures of the thermostat open and closed. Does the 03 FSM have similar pictures? When the stat is open it blocks the bypass passage. If you were to pull the stat then both passageways (the bypass and the one to the rad) would be open. Fluid flow would take the path of least resistance which would be the bypass.

 

[rbattelle]

Does the 03 FSM have similar pictures? When the stat is open it blocks the bypass passage.

Can't find it, but that doesn't mean it's not in there. What section is it in?



I checked the Cummins manual (should've done that first) which has really nice diagrams and Brods is absolutely correct, as usual. There is a bypass that flows coolant to the suction side of the water pump when the thermostat is closed.



Ryan

 

[JWadford]

the engine itself can overheat with no t-stat because the coolant will flow too quickly through the radiator to dissapate heat to the atmoshere, but on the flip side it will take light years for the coolant to warm up unless it is warm outside, also the coolant will be running too quickly through the cylinder head and block to pull the heat out of the engine making it possible to have a hot engine, cool coolant condition, hope im not confusing anyone im not good at explaining things

 

[rscurtis]

You may want to re-think your position on this. The reason the B engine in marine trim can develop so much more power than it does in a vehicle is because of the tremendous volume of water available for cooling. More flow = more heat transfer, even though the transfer medium may be cooler that it would be at lower flow volumes.

 

[TSham]

Thanks for the replys This clears up the difference from the bypass on a gas engine.

 

[CKelley1]

jwadford is 100% correct on this one every good mechanic has known this for many years. if a t stat fails in the field and you need to keep using it . get a beer can out of the back of the nearest truck and make a plate with a small hole in the middle that is about the same size as the open area of the t stat. your back in business and no overheat. and the t stat bypass is to keep the block heat evenly distributed