Overheating problem please help!

[dropped81]

Okay guys I'm new here and really need some help on figuring out why my trucks temp gauge fluctuates. I can drive for about 10 min and the truck will be around 230 degrees. Than all of a sudden the temp will drop down to about 205. I have a 195 thermostat in it i just replaced. also just replace the radiator so i know its not that. Water pump looks fine from what i can tell don't see any leaks. I'm gonna try a flush tomorrow to see if maybe there's an air bubble. Any help is much appreciated. Thanks Mike.

[72freak]

Mine does the same but not as high....Sounds like the thermostat to me....Its reacting slowly.

[dropped81]

i just replace the thermostat its the second one in about 6 months. I'm kind of wondering if it might be my coolant to water mixture i know it can cause your truck to overheat. and its not overheating severly.

[donut]

Any steam rolling out? How accurate are the gauges?

Mine will spike a little high, then drop back when the thermostat opens. As long as your coolant is close to abt. 50/50, that shouldn't be an issue.

[Pop's C-10]

fan clutch maybe?

[chrismoore701]

2nd the fan clutch. are you sure you have the right radiator. I think they come in 2, 3, and 4 cores. good luck

[hatzie]

Originally Posted by dropped81

Okay guys I'm new here and really need some help on figuring out why my trucks temp gauge fluctuates. I can drive for about 10 min and the truck will be around 230 degrees. Than all of a sudden the temp will drop down to about 205. I have a 195 thermostat in it i just replaced. also just replace the radiator so i know its not that. Water pump looks fine from what i can tell don't see any leaks. I'm gonna try a flush tomorrow to see if maybe there's an air bubble. Any help is much appreciated. Thanks Mike.

If you're not blowing out steam you may want to verify the actual engine temps.
Factory gauge senders aren't always accurate especially after 23+ years.

If the temps are real then start by checking the clutch fan operation and how much crud is in the radiator.

[Eyegore]

You may also want to consider the water pump, it seems you have a restriction somewhere. In my 86 in stop in go traffic it never overheated but when i ran it down the freeway at higher rmp then it would overheat. Also when it begins to heat up kick on the heater and see if the bypass into the heater core cools it down.

Tom

[JBRAVO383]

Has the water pump been replaces recently?

on my 85 There was a v-belt water pump on my 383 when i was running a serpentine set up. In-which a serpentine set up runs the opposite way a than a v-belt set up. But my temps were fluctuating 185-225 and when i would rev it up my upper radiator hose was being sucked shut.
This may not be your problem but just something to look into.

[jrcaprai]

Do you have a Fan Shroud ???

[dropped81]

Thanks guys for all the responses. no steam is rolling out and the gauges are dead on accurate they are aftermarket not stock. Chrismoore701 and pop's c-10 i know the fan clutch has a bit more play in it than it should but its still working fine for now its on the list of things to fix, but also would the fan clutch cause the temp gauge to fluctuate like it is. Also chrismoore701 i didn't even think about the radiator rows. I think you might be on to something my old one was a 2 row and my new one is oly 1 row and none of this started until i changed the radiator. even when it had a pretty good sized leak in it the temp still never got hotter than 195. and yes there is a fan shroud i ran with out one for about a week and realized i should probably put it back on i didn't realize it made as big of a difference as it does lol.

[Eyegore]

I know were only a couple of days into spring but how hot where you are at? If the probleml started after you installed the one row, it sounds like that radiator has some sort of restriction in it. I would take the lower radiator hose off and run water through it to see if it frees something up.

[dropped81]

I just did a flush on it and nothing came out and the weather here is still a bit chilly but the truck is still getting up to about 230 or 235 than dropping down too about 205-210. I think it has something to do with this radiator.

[dropped81]

Also my passanger side floor is dry but do you think it could be something in the heater core?

[85Bowtie]

It sounds to me like you have air in the system. Are you sure you're getting all the air out? What you will have to do IIRC (been a long time since I looked under the hood of mine) is jack the front of the truck up so the radiator is above the intake. Open your radiator cap and run the truck up to operating temp with the heater on high. Any air in the system will go to the highest point, which is at your radiator cap.

Is the overflow filling up at all? If so, you may have a bad head gasket. If it is a small leak on the cylinder side, the pressure from inside the cylinder is enough to keep the coolant from running into the cylinder. Instead, it will push air/exhaust into your coolant system because of the greater pressure. This will displace t he coolant in your system and give you an air pocket which does exactly what you're describing. If so, when you have the heater on you would notice it blowing cold all the sudden.

[dropped81]

Thanks for the info 85bowtie ill check it out tomorrow when i get some time.