I just made a 3 hour round trip. Half of it pulling 6-7k on my trailer.


Based on my Auto Meter water temp gauge, It was running 210-211 cruising, and didn't change when I would get in it, or coasting in gear down a 4 mile grade. When I got home, the top hose was hot, butthe bottom hose was COLD, 40 degrees ish.

Is that normal? It seems like the thermostat is not opening soon enough It is a Napa thermostat ( about 10,000 miles old)

 

Time to get it boiled out / rodded or replace it. Cold on the bottom means its all clogged up. IIRC!

 

That would make sense. Doesn't the coolant circulate bottom to top through the radiator?

 

did you have heat in the cab? the bottom hose is directly out of the pump is it not???

 

Yes, I have heat (new heater core) but the lower hose (running from the pump to the bottom port on the rad) is cold, while the top one is hot.

 

Top to bottom I think. I used to have a pic but I can't find it.


The engine cooling system operates in the following manner:

Engine coolant flows through the radiator tubes and is cooled by air passing over the
cooling fins assisted by the cooling fan.

Coolant flows from the radiator to the water pump, through the engine front cover to the cylinder block, cylinder head, oil cooler and on to the water thermostat.

Coolant also flows from the engine and from the top tank of the radiator into the degas bottle where air and combustion gas is removed from the coolant. The degassed coolant is then returned to the water pump.

The degas bottle has a fill cap to allow coolant to be added to the cooling system.

Best I can do at the moment.

 

Nice explanation! I guess my question now is: If the coolant goes out the bottom of the rad., Wouldn't it be cool after flowing through the rad? But I guess it should still be warm.... Sorry, I am kind of thinking out loud here....

 

Thats the idea. When its cold as you described it the flow is limited. I'll find that pic eventually. Is yours the the degass type or does it have a radiator cap. I know it changed at some point but I don't know when. I think the older ones had copper radiators. Like the IDI 6.9.

 

I have the degas type, with the plastic tank radiator. Come to think of it, I have the third small hose that tees into the heater hose plugged at the radiator, and just straight heater hose from the head to the core. Could this have any effect on the system. I am sorry if I am confusing....

 

Just a curious question, is your aftermarket temp gage hooked up to its own independent temp sensor and if so where is the sensor located? Is the gage on the instrument panel reading normal? 210 is not really that hot especially when you're pulling a heavy load up and down steep grades. I'm pretty sure your bottom hose will be cooler than your top hose, but not dead cold.

 

Yes, I do have a separate sender for the aftermarket gauge. It is located in the side port of the water pump, right below the thermostat neck. Yes my stock gauge reads fine. It rides on the top side of the O in normal.

I know that 210 won't hurt anything, but based on the 203* thermostat I wouldn't think it should operate that much higher than the opening point of the t-stat.

 

The fact that your lower hose is cool to touch is a good thing. That means that your radiator is working well. Hot coolant enters the top and is cooled by the airflow as it travels down the tubes. Ideally, by the time the fluid reaches the bottom tank it will be the same temp as the air flowing through it.

The thermostat neck is probably the highest temperature the coolant reaches in the circuit, as it is just leaving the motor heading for the radiator.

 

Flow thru the radiator is from top to bottom. Efficiency is higher when you don't try to fight thermodynamics and gravity. The coolant will tend to 'drop' as it liberates heat so the lower hose will be cooler when the radiator is functioning correctly. (this is one case where an IR temp gun would be useful.) Sounds like 'how much cooler' is the real question. I know these radiators are a bit oversized but I wouldn't expect the outlet temp to be close to ambient with the flow rate of the pump.

 

if you are running a napa t-stat, your motor should be running between 180 and 185 if not lower. you should be pretty steadily at or under the N on normal on your regular temp gauge. The stock t-stats are 190*, which means they open around 170, normally they keep the motor too cool, which is why dieselsite crated the 203* thermostat. If you have a napa t-stat in your truck and you are running at 210 then something aint right.

 

94-95 Trucks use the 203* t-stat from the factory, 96-97 have the 195*.

I have the 203*

Do people think this might be a faulty t-stat?