77 K-10 Overheating

[caldar]

Hey all, looking for some advice on the coolant system.  Have a 77 k-10 1/2 ton 350 with a brand new rebuilt engine, new hoses, new t-stat and am having some problems overheating.

Symptoms
Right now she starts up easy and idles strong.  During the morning commute she can make a 45 minute drive (in 45 degrees) just fine.  On the way home, though (75 degrees outside) engine power will start to fade after 15-20 minutes, requiring me to pull over, open up the hood and let the engine cool for 20-30 minutes.  Also, temp gauge shows a normal 180 range so there's probably something wrong with that as well.

Known Facts
- Radiator has no leaks and no coolant leaks anywhere else.
- Temp gauge shows ok temperature, but clearly something is wrong
- Water pump appears to be working ok
- When running without the radiator cap the top hose feels hot, the bottom cool, as expected.

Possibilities
- Bad radiator cap that is not allowing the coolant to pressurize
- Serious air bubble in the coolant somewhere
- T-stat is staying closed (although this part came like-new with the new engine)
- Timing too advanced, running too hot for the coolant system to keep up

Any help on this problem would be greatly appreciated and let me know if any more information is needed.  Thanks.

[jaredts]

So your only real symptom is loss of power on the afternoon commute?  Is it possibly a slipping transmission?  Do you have any other reason to believe that its overheating despite the temp. gage?

[caldar]

Hey, thanks for the reply.  Transmission has been professionally rebuilt, so I don't think that's involved, but I could be wrong.  I should also mention the heater doesn't work, which could indicate no coolant flow through the engine, correct?  The only thing is that it just feels REALLY hot when opening the hood, way more than normal, but other than that there's no other symptoms. 

Thanks again for the help.

[Layne]

Get one of those spill free funnels, and a new stat. Test it in a pot of boiling water. Maybe flush the heater core.

[VileZambonie]

Is it actually overheating? Is it boiling over? The lower radiator hose should not be cool when the engine is at operating temperature. Do you have a catalytic converter?

[liftedchevys87]

What heads are on it?

[caldar]

Hey all, have an update.

Last night we replaced the thermostat (which was faulty upon doing a boil test), got a new radiator cap and flushed the coolant.  Feeling the hoses and a constant temperature reading on the gauge at around 200 shows that the coolant system is all good.  No burning oil on the engine or anything like that.

However, the problem of the engine stalling has actually gotten worse.  Now it's clear it most likely has nothing to do with heat since it wouldn't run more than 10 minutes at a time around the block last night.  Looking at a repair manual, it suggested replacing the distributor rotor, which is in fact old and has some corrosion.  Trying to narrow down the cheap and easy-to-fix options first, so my roommates and I might try that tonight.  Any thoughts on that, guys?

Thanks again for the comments.

[Lt.Del]

when it stalls, does it fire right back up?  Or does it have to sit for a while prior to firing back up?   I think a bad pick up coil in the distributor if stalls when warm and won't start back up 'til cooled.

You tstadt was malfuntioning but your guage said 180 degrees?  Get a new temp. sender or check your guage.

When it stalls, and if it can't fire back up immediately, check for spark...pull a spark plug out and ground the tip to the engine head or somewhere and have someone turn the engine over and see if it sparks.

[caldar]

Hey there, so if it's been sitting a while it will start up relatively easy after a stall but it will have to sit longer and longer before it will start again the longer it's been running.  Sounds like you might have the right idea.

We'll definitely check the spark plugs and maybe try a new coil as well.  Really appreciate the help!

[Lt.Del]

try a new coil as well.

See if you get fire when it stalls when motor is warm. If no spark, it may the "pick up coil", versus the ignition coil. The pick up coil is around the shaft of the distributor, under the rotor.

the pick up coil is what the module in the distributor plugs in to.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=15628.0

[caldar]

Hey all,

Some more updates for you guys.  Same problem is occurring, the truck will start up consistently and runs/revs strong for about 2 minutes and then acts like it's out of gas, then dies.  Will restart after a few minutes, then the same thing.

What we've done so far:
- New radiator cap and t-stat (not cooling problem)
- New distributor/pick-up coil/spark plug wires
- New fuel pump
- New head gasket (came with rebuilt engine)

We've pulled the fuel line off the carb and attempted to start it, and we get a good spray of fuel from the line so gas is definitely getting to the carb.  Could it be as simple as a gummed up fuel filter?  Also, one thing I forgot to mention.  The carb came from a 400 and this engine is a 350.  Could it possibly be a jetting issue?

[VileZambonie]

You replaced the ignition coil or the pick up coil?

[caldar]

Hey there, thanks for the reply.  We've replaced the pick-up coil, but no, not the ignition coil.  I guess since it starts up fine we hadn't considered that.