I was pulling my boat to the lake the other day when my engine temp quickly rose to the max. This caused the cap on my coolant overflow tank to pop off spilling coolant down the side of my truck. I was thinking the thermostat. Any other ideas?
DT
Could be headgaskets, electric fan, thermostat or something blocking airflow thru the radiator.My guess with out knowing the type of truck would be headgaskets…
possibly your fan is not turning on(temp sensor, a relay) or something blocking airflow through your radiator. or your thermo stat could be sticking shut then opening causing the coolant to boil over!
Maybe Trumar will chime in on this one. Correct me if I am wrong but if it is the head gasket you will have pressure in your radiator. So if you run the engine with the radiator cap off you will get bubbles inside to radiator. And if you have the cap on if you turn a hot engine off water/anti-freeze will run into the oil. If I remember correctly if your oil is foamy or has bubbles on the dip stick this is a sure sign that the head gasket has blown.
what make of truck??????? what engine??????????? then well work on the diagnosis!!!!!!!!! not to be a smart a– but this does help A LOT 
Waterpump or thermostat, when the engine is running feel the hose going from the radiator to the waterpump if its hot with fluid running through its the thermostat stuck closed $20 dollar fix, if no fluid is going through its the waterpump. Hope that helps!! GOOD LUCK!!
I didn’t want people to get jealous, thats why I didn’t post the make. 
1992 Ford F150 with a straight 6.
DT
I pulled the dip stick and it was nice clean oil.
DT
Maybe run the motor with the cap off…if it has a cap and if you can see the water/antifreeze in the radiator, see if it starts to flow after the engine warms up.
fwiw I found the discount stores sell junk thermostats, so if you replace it, get a good one, Ford or I’ve had decent luck with NAPA stats, don’t forget a gasket too.
Al
Quote:
I pulled the dip stick and it was nice clean oil.
DT
300 six cylinder that is a good strong motor that will run forever. Change the thermostat and gasket, it is easy and cheep. Just make sure that you have everything aligned before tightening so you don’t break the thermostat housing, Tony a friend cracked his once. 
Once done check your anti-freeze to make sure you have the correct ratio to water. And you should be good to go… 
As I was going to put in the new thermostat today I noticed that I could spin my fan blade with the vehicle off. I;m assuming you aren’t suppose to do this as I don’t remember being able to do it on other vehicles. Would it be the fan clutch?
DT
Never mind. According to the Haynes manual its working properly.
DT
Quote:
Never mind. According to the Haynes manual its working properly.
DT
As reading through this post.. My 1st place of checking for the problem would making sure the radiator fan clutch is working properly..To test it have the hood open and start your truck,let run for 20-30 seconds and shut off ,if you can get out of the truck and see the fan spin ,replace the clutch. If working right it should only spin just a few times after shutting off.
2nd.. I would replace the thermostat and gasket as mentioned and make sure you antifreeze is good and at proper level.
As mentioned those are outstanding engines with the right care. 
The blade stopped after shutting off the truck. I will replace the thermostat tommorrow.
Thanks, DT
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