Braggs

Can someone tell me how to mitigate the heat soak issues on my truck? It's been like this since I've owned it and haven't been able to fix. Here's what happens:

Starts fine, runs fine, temperature gauge stays right in the middle. When I stop and turn off the vehicle, I can turn the key back to ON and watch the temperature gauge slowly creep up until it gets to almost the hot line. If it try to start it before it cools back down, it has the "hard cranking" sound with pauses between turns. Still, it will turn over and start after a few very slow cranks and the temperature gauge will come back down after water starts circulating again.

What I've done to the cooling system: Replaced water pump with HD water pump, thermostat, fan clutch, and radiator hoses.

Thanks!

Chris_1

iTrader: (1)

First off, is it really getting that hot ? The temp gauge is just getting it's signal from a little resistor in the sender unit and that may not be reading right. If it is getting hot after shutdown but not while running, I'd maybe suspect some air in the system. Nothing is happening after shutdown to create more heat, there's just maybe residual heat radiating out, but not so much that it should overheat the engine.
The temp sender should should be on the front left of the lower intake. Not to be confused with the temp sensor above the thermostat housing on EFI engines.

As for hard cranking, often the starter gets hot while running and won't crank well until it cools down. A weak starter will work better cold than when it's hot. It is right beside the exhaust. So maybe a possibility there.

Another thing that happens with EFI engines (you didn't say if yours was) is that the injectors or fuel pressure regulator leak fuel into the intake after shutdown and load up some of the cylinders with fuel making for a hard crank. another possibility if you have EFI.
To test for that one, you would need a f/p gauge. Turn the key on to pressurize the system then turn it off and watch to see if it will hold that pressure for more than a couple of minutes.
Those are some things to have a look at anyway.

Braggs

It's not an EFI, it's carb'd. I replaced the temperature sensor also when I first got it (gold colored plug on the front-driver's side of the intake manifold) and also the radiator cap at some point in the last couple years.

Did you suggest replacing the starter to fix the "hot/weak starter" issue? Would the same thing happen to the new starter?

Chris_1

iTrader: (1)

You might want to at least pull the starter and take the end plate off to have a look. Brushes could be about wore out or like an old GMC I had (a 76 ?) with a hot crank issue the starter was coated in oil inside - total mess.
It does have a cranking issue so before getting too excited about anything else it might be a good idea to either throw a rebuild at the starter or get a new one.
The parts inside a starter are only good for so long before the brushes and such wear down to nothing so if it doesn't look pretty new inside, it's about time.
An old starter will work right up to when it doesn't anymore. Getting ahead of that curve can save you the cost of a tow truck ride so it's a good investment. And may just solve your problem. Or at least eliminate it from the possibilities.
Won't be a waste of time or money either way.

DrinkinGasoline

Two things might help out. A carb spacer and a gear reduction starter (ensuring that the cables are good with solid,clean,bare metal connections). Summit carries both.

84ordF150

Let's back up a bit....Define "heat soak". I've been around engines for 40 years and have never heard the term.."heat soak". Vapor Lock, yes...Carb Icing, yes...Fuel Dump, yes....
but Heat Soak ? Are You trying to describe high engine temp possibly contributing to fuel delivery issues?

burnthelight88

Ditto on the PMG (gear reduction) starter. Easier to get back in where you need it, better torque for starting, reportedly less susceptible to heat.

Chris_1

iTrader: (1)

I agree that the gear reduction starter is a good idea but sometimes it requires a rewiring of the circuit which is often more than some people might be up for.
Original starter worked just fine for a lot of years, so for myself personally if I was going to change the starter in an 86, I would put a stock 86 starter in.
Simpler is all.

Braggs

Heat soak is when the heat from the engine during running soaks back into the engine after it is turned off. While it's running, the heat is removed by the circulation of water. After it's turned off, there's no water circulation or heat removal which allows the built up heat of the metal to soak back into the water causing the temperature of the water in the engine to rise (and subsequently show on the temp sensor inside).

I'm not getting any vapor lock (where the heat boils the gas inside the fuel line causing an air bubble), nor carb icing (too warm of climate), and the engine stays at a normal temperature when running.

Braggs

I have a partial solution for my "hard cranking" issue (where the starter struggles to turn the flywheel/flexplate) when hot. Recently I rebuilt the transmission (due to burned clutches, old seals, failure to shift into forward gears when cold, etc) and also replaced the torque converter and flex plate at the same time. Just got it back together last night. Now the cranking (even when hot) turns the engine quite fast like there's no tomorrow. Perhaps there was some friction from the transmission side of the flex plate causing the bog?