I own a 1997 f-250hd with 157,000 miles.
I just purchased this vehicle and am in the process of correcting many issuies due to the neglegents of the previous owner.
I am stumped on this one.
The engine will not achieve operating temp 190-195 degrees.
nor does the heater provide sufficent heat due to the low operating temp 150 degrees.
I have flushed the system, Changed the thermostat and ensured that all hoses are routed correctly.
Can anyone help?

 

Here's what I can think of in the most likely order:

A. Thermostat is stuck open
B. Thermostat purchased is the wrong temperature
C. Cooling fan running all the time
D. Radiator is not original and larger than it should be


I'm leaning towards one of the first two. What type of fan do you have? Is it clutch or electric? Also, are you mixing antifreeze with your water? Plain water by itself will run cooler than water with antifreeze in it. Also, see if you can verify the temp by sticking one of those cooking thermometers down in your radiator. It could be that your temp guage/sending unit is giving a false reading. I know that you said you had no heat as well, but sometimes that can be caused by another problem like a blocked heater core or a vacuum valve that isn't opening up. If your coolant in your radiator truely is 150 degrees then I say 95% its some type of thermostat issue, either sticking or improper opening temp.

Lloyd

 

Thanks loyd, Unfortunatley I have exersized all thoses options that you mentioned. I am a Marine Mechanic and have some sophisticated tools i.e. digital thermometers etc.
Marine cooling systems are quit different in design however the same principles apply thats why I am so stumped about this.

The thermostat is oem from ford
The radiator is stock
The Thermostate housing was lapped on my lapping table since it was slightly warrped to ensure no leaking
The Airflow door was checked
The fan is a centrifical type.

Thanks again for your thoughts I would welcome any more.

 

I had a similar problem on a 300-6 engine and had checked everything you did. Found satisfactory relief for several years by installing a 205 degree thermostat.

I accidently found the cause of the problem when I installed an exhaust manifold gasket(not used during factory assembly)and a fiber exhaust pipe gasket(steel gasket is factory standard). While both mating surfaces may have been tight when the vehicle was new, over the years some audible leaks had developed at both locations. After seeing the temperature gage run at the high end of normal, I reinstalled a stock 195 degree thermostat.

Not sure how exhaust leaks at other locations or exhaust system modifications affect heat retention at the engine. On my truck, the exhaust system is stock without observable leaks.

Good luck with your efforts.

 

Thanks , Ill look into that

 

I hate to repeat what I said before, but after reading about exhaust leaks lowering water temp, I think we need to go back to basics here:

Let's say I install an aluminum 'block-off' plate where your thermostat is supposed to go. What happens? Engine overheats. Why? Because there was no way for the water to circulate through the system. Now let's say I take out the thermostat completely. What happens? Needle never leaves the cold mark. Why? Because the water is circulating too fast and overcooling the system. So what sets the temperature in your system? That little $2.99 thermostat that you picked up at the Ford dealership. Now, I don't care who makes it, the design of the thermostat used in vehicles today is one of the cheapest pieces of crap I have ever seen. I once got 4 bad thermostats in a row from an auto parts store before finally getting one that worked. Just replacing your thermostat with a new one does not rule it out of the troubleshooting procedure, trust me. Also, If you rush the job and don't install it just exactly perfect it can get 'stuck' as well. It's real easy to bump it and shift it out of place when you're trying to get the thermostat housing bolted back on. I know its a pain, but I would seriously consider taking your thermostat out and trying another one (exchange it if you can) before I did anything else. Make sure you take your time installing it and make sure that it is straight in the bore. If this doesn't solve your problem then call me an ******* and an idiot and whatever else you want, but I really think it will fix your problem. Best of luck.

Lloyd

 

Thanks , I will try another t-stat, What about the by-pass loop from the water pump to the housing?

 

The bypass loop doesn't flow enough coolant to cause an 'overcooling' problem. If the bypass loop were clogged then it could possibly cause an overheating problem, but since you're definately not having that issue then I would say you're fine in that area. Basically, the bypass loop is just there to equalize the pressure on either side of the thermostat when it is closed and give the water somewhere to circulate thus relieving pressure on the water pump and keeping it from dying an early death.

Lloyd