Radiator intermittantly overheating. A bit long, but here's the symptoms...

*Start up and drive away, engine heats up fine, heater blows plenty of hot air.

*For no apparent reason, my heater starts to blow cold air...then engine overheats (idiot gauge into red zone).

*a minute or two later, heater starts to blow hot air again, and engine cools off (idiot gauge into normal zone). Sometimes it doesn't cool down at all until I shut it down.

*it may overheat again that trip...it may run fine the rest of the trip...oddly enough, it may not overheat at all for a few days.

*I get an occasional check engine light but haven't been able to run a code on it.

What's going on??? I've replaced the t-stat, pump, upper and lower hoses, radiator overflow cap, flushed and filled with new anti-freeze. Nothings fixed it. What else can go wrong with a radiator?

Old fluid looked rusty (thanks to the previous owner). Flushed until clear. Replaced the heater core two years ago...could that have gone bad that soon? Could something be clogging up the radiator or heater core intermittantly and causing this problem?

I'm at a loss...begging for help here.

Recently installed electric fans...could improper thermostat adjustments cause such a headache? Fan 1 turns on at about 185* (about 200* actual water temp I believe), the other about +10* over the first.

As always...any help is greatly appreciated

 

Do you still have a mechanical thermostat in the engine?

 

The sudden cold air is still a circulation problem. The heater core is not being fed hot coolant. I've never heard of an intermittent blockage, but you are definately having a problem circulating coolant back to the heater core.

 

Yes...still have a mechanical t-stat.

 

You never said anything about loosing cooland so you must not be. The over heating could be caused by the fans not turning on at the proper temp. Then when they do it immediately cools down the coolant. But the fact that you have no heat is a sign of blockage as was mentioned or an air pocket. The next time it over heats check the coolant level and see if the fans are running. I had a simular problem but I still had heat. It turned out to be the rad. The top 4-5 rows were blocked so the probes never saw hot water till it was too late. It eventually ballooned the rad and caused a leak at the tank.

Regards

Jean Marc Chartier

 

I don't know beans about electric fan cooling but it seems to me that a mechanical t-stat is not needed since your other thermostats for the electric fans should turn the fans on and off as needed to keep the coolant at the correct temperature.

Did you get install instructions with your electric fans?

Where did it say to mount the thermostats for the fans?

Maybe the mechanical t-stat is ok since one is included with this electric fan install...

http://www.customracer.com/lightning_engine.html

 

temp1,

Only JDM offers a replacement T Stat. If you look at his sig you will notice, last item, Troyer Performance fan kit. No T-stat is provided with this kit. Regardless a T-stat is required to keep the engine at the correct operating temp. Without one, one of two things will happen. Either the engine over heats because the coolant doesn't stay in the rad long enough to cool off or the engine never reaches the correct temp becasue the lack of a t-stat allows coolant to flow to rad and stay below operating temp.

JMC

 

Thanks for all the info, but...

Seems that I have a bigger and more serious problem. (read the TERRIBLE Clatter thread).

Started the truck after work and it's making a machine gun sound under the hood. I figure it's not good...perhaps a rod gone for a late day jog inside the engine.

JMC...
you have a very good take on these engines. This clattering sound...Timing chain gone bad there are now serious internal problems? And how serious / costly is this going to be? Could this at all be related to the problems of intermittant cooling and overheating? Never did lose coolant except a little bit at the overflow tank as the pressure built up and released. The fans do run when it's overheating, so the radiator is being cooled. Perhaps there was an air pocket within the block...I did seem to hear a bit of gurgling when I turned the engine on. How does an air pocket develop, and how much harm can it do? I suspect alot!

Temp1...
the instructions say to mount the sensors close to the inlet of the radiator (top left as you face it).

Thanks to all...

 

Not to scare you, and hopefully im wrong... but those are classic head gasket failure symtoms.

 

Did you read his other post? It does not sound good...

Hydrolock coming?

https://www.f150online.com/forums/sh...hreadid=141777

 

Hydrolock??? If it costs less than a head gasket...I'll take it

 

Hydrolock...... This is when a cylinder fills up with a liquid. Now we know that air, and air/fuel mixture can be compressed, but a liquid can not. So, when your piston comes up, and your valves close, it tries to compress the space, if the space is being taken up by lets say..... coolant, and it cannot be compressed, somthing has to give. That somthing is usually a rod. But again, this may not be what you have going on.

 

Hydrolock is when coolant from a internal leak get into a cylinder and fills it. When you go to crank the engine the coolant compresses and keeps the engine from turning ( very bad) Of course, if the head gasket was putting exhaust gas into the cooling system it could explain your loss of heat( heater core fills up with air instead of coolant and the overheating. Take it to a shop with a gas bench and have them check for exhaust gas in the cooling system ( there are chemical tests for this also but the gas bench is the quickest way.