Intermittent overheat.

[jhamelton]

Working on a guy's truck and twice he has left my house, got about 5 miles down the road, and it's overheated. The first time, I did some cosmetic work and replaced the valve covers. Ran it in the garage for about 30 minutes, drove it for about 30 minutes, all good. Guy picks it up, 10 minutes later call me. Truck overheated. Went to his house a couple days later, put in a new 160 thermostat. Filled and drove it for about 30 minutes. All good. Guy called again two days later. You guessed it, overheated again. So it only overheats every now and then. I don't know much about the truck. I believe the motor is stock. I've included the only pic I have of the engine bay. 4 barrel carb, stock intake. Intake, radiator, water pump and raised thermostat housing are all chrome. Don't know if that helps any. It has an electric fan that is hooked up to run all the time. Stock temp gauge. Sensor is in the intake, next to Tstat housing. Gonna get more info from the guy tomorrow. Any help is appreciated.

[MiraclePieCo]

How do you know it's overheating - does it actually boil over, or does just the temp gauge climb? If the latter, I'd suspect a faulty gauge or sender.

Also, it doesn't appear to have a heater; is there a bypass hose connected between water pump and manifold? I have found that coolant will flow through bypass hoses, thus circumventing the radiator so it doesn't get proper cooling.

Other than that, intermittent overheating is usually fan or thermostat related. You installed a new thermostat, so have you verified that the fan doesn't have a bad connection somewhere? Is it actually running when the truck overheats?

Could also have an air pocket stuck in the block or heads. Use a Spill-Free Funnel system to get all the air out.

Good luck!

[OrrieG]

Ditto on the gauge. My Chevelle started overheating a couple of years ago, turned out the sending unit was failing showing 10 degrees hotter than the engine was. Also agree with the other comments, with air bubble being the highest. I also drill a small 1/8 hole in the thermostat stat to allow for air to bleed out. Take a look at this current thread too:

http://67-72chevytrucks.com/vboard/s...d.php?t=681362

[mr48chev]

I'd agree with them. First do you know that it is actually overheating or is the temp gauge just climbing to around 200 which for that engine isn't overheating?


Years ago when I worked in a shop we had a problem child Camaro come in the shop that was oveheating and we couldn't figure it out at the time. Someone had swapped an older 350 into a 3rd generation Camaro complete with V belts on the engine and then when the waterpump went out the then owner or shop that worked on it replaced the pump with one for the year model of the car rather than the earlier engine that had V belts, reverse rotation pump. This thing held temp great sitting and idling in the shop and at low speeds around the block it wasn't bad but get it on the freeway and the temp gauge shot up right now. I moved on to a different job about that time and a month later an article in either Hot Rod or Car Craft told about that same problem.

Are you sure that the engine has the correct pump for the belt setup that is on the truck?

On the gauge sending unit thing, years ago my best friend had a Model A roadster with a mildly modified small block in it that he thought was overheating. His temp gauge was reading 265 but he stood in front of the car with no shirt and undid the radiator cap and not one bit of coolant came out under pressure as there was no pressure. It happened that we were at a car show and the Walker Radiator rep was there pushing his products and the car had a Walker radiator. I ran across my Snap On man who had his truck in the parking lot and he sold the rep a thermometer to stick in the radiator and read the temp. It was 2 degrees above what the thermostat was set at on a 100 degree day. Electric gauge with a bad sender.

[55dude]

get you a infared heat gun and check various spots on block,heads,radiator, hoses... when running, sounds like trapped air.

[my56chevytruck]

Originally Posted by 55dude

get you a infared heat gun and check various spots on block,heads,radiator, hoses... when running, sounds like trapped air.

What makes me suspicious of this truck overheating is you run it in a garage for 30 minutes, fan's going and no problem. your friend drives it and it overheats. I own an infrared laser heat gun and find that most gauges are off by as much as 15 to 20 degrees, may not be all but most are. why do you think they've removed the increments on the temp gauges?? secondly, what is overheating to your friend?? I'm assuming the fan is pulling or pushing air into or thru the radiator?? how much coolant to water is he running?? 50/50 is ideal. Bleed the entire engine and radiator and refill, then see what happens. and lastly, I too have drilled 1/16" holes around the thermostat inside the mounting flange for constant flow. makes a difference

[OrrieG]

Originally Posted by my56chevytruck

why do you think they've removed the increments on the temp gauges??

I used to think my modern cars had the most consistent cooling systems before a shop mechanic pointed out that they are basically a graphic idiot light. If the temp is in a range say 140-210 they stay in the middle, if it over heats they go to hot. I always run aftermarket analog and fluid gauges.

[mr48chev]

I'd go back to the "is it really overheating" Is it actually overheating or is the gauge just reading a tad higher then he thinks it should and that is sending him into a panic. For some reason a lot of guys coming to old cars and trucks pee their pants every time the temp gauge gets anywhere close to 200.

I'd go for a ride with him and see what it is actually doing and take a heat gun with me if you have one. Find out what is actually going on and go from there.

One thought though is that the bottom hose might be collapsing and causing a restriction when the engine is at road speed for a while.

[1-ton of fun]

orrie, oil pressure gauges in many new cars work the same way!

[jhamelton]

Thanks for all of the input guys. It is much appreciated. I am going to get the truck tonight, and drive it like I stole it LOL. After talking with him he doesn't really know much about it, and I think he just thinks it is overheating. I'm going to put an aftermarket gauge in it, and a new and a new high flow water pump. He did say the guy that put it together put a water pump off of a drag motor that he had, so I don't know what it is exactly, so figure I will start fresh.
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[1project2many]

F*rd really started it, the "idiot gauge" trend that is. Ever notice they have a giant range for "normal" and very small areas at each end of the gauge outside "normal?" It solves a whole lotta questions when the dealer guys can say "Well, yeah, but it's still normal."

[jhamelton]

Just got it home. Gauge stayed at 3/4 the whole drive which is about 15 miles. After I stopped and let it idle in my driveway, the gauge pegged to hot. Popped the hood. No boiling, no steam. Used my infrared gun and there was nowhere that the temperature was over 200 degrees, except at the sender next to the thermostat was about 210. The gauge is a liar! Lol. Still gonna put a pump on it for him with an aftermarket gauge. Any recommendations on pumps? It has a chrome shorty on it now with the adapters to space it out like a long one
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[MiraclePieCo]

Glad to hear it's okay. I've had high-flow water pumps create more problems than they solve - sucking lower hoses flat, circulating water too fast through radiator, etc. For mild street engines, I prefer stock water pumps.