Way above my paygrade

[flyboyjack]

Hey guys, ('n gals),
Here's what I've got going. All original truck with a 350/350 and 110,000 miles started running a little hot in stop and go down here in south Florida. Put in new fan clutch and high volume water pump. Flushed radiator and new coolant and "water wetter". Then replaced OEM quadrajet with professionally rebuilt q-jet. Set timing and rechecked. Tuned q-jet with vacuum gauge. The old mpg's were 10-11 around town and 14.5 to 15 on the road. Did a 400 mile road trip. Got 12 mpg! Also the truck ran warmer, (not hot), just warmer than usual. However once back in stop and go traffic, temps cooled back down to normal. (I'm estimating a 15-20 degree drop and rise). And now in my suburban driving mpg's are 13+!!! and 12 on the highway. Just again did a short jaunt on the freeway. Temps back up,...once back in the city, temps back to what I know to be normal. Also top end above 65-70 mph, power seemed to be gone and I used 1 1/2 quarts of oil in 400 miles. Again, once I'm back to suburbia, oil consumption back to 1 quart/1000 miles. Looked for vacuum leaks. Rechecked timing. HELP!!

Jack

[Chevyland]

Maybe , rodding the radiator ?

[57taskforce]

There’s a lot going on here. I’m wondering if your higher temps at speed are due to the high volume water pump pushing the coolant thru the radiator faster than it can pull the heat out, hence why at lower rpm stop and go it cools like it should. A stock replacement pump should be adequate as long as all the other components in the system are functioning properly. For the oil consumption I’d check the pcv system over thoroughly before anything else. Lots of consumption issues end up being related to pcv in one form or another.

[LockDoc]

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I don't know what you are running for a thermostat but that would be my next replacement. Have you checked the temp with a digital hand held thermometer? I think your local auto parts store may do that for you if you don't have one.

LockDoc

[geezer#99]

No power on the top end can mean your carb is leaner and your timing is retarded.
Jetting and metering rods in your carb may be leaner. Hard to check unless you take the carb apart.
Timing is easy to check.
What’s your initial timing and what distributor?

[garyd1961]

Originally Posted by 57taskforce

There’s a lot going on here. I’m wondering if your higher temps at speed are due to the high volume water pump pushing the coolant thru the radiator faster than it can pull the heat out, hence why at lower rpm stop and go it cools like it should. A stock replacement pump should be adequate as long as all the other components in the system are functioning properly. For the oil consumption I’d check the pcv system over thoroughly before anything else. Lots of consumption issues end up being related to pcv in one form or another.

There is no such thing as pushing the water too fast through the radiator. It's just some internet wise tale. You can push it too slow but not too fast, unless you start blowing out hoses or something. Been working on on cars for over 40 years and I have never heard of buying a low volume water pump but they do sell high volume pumps.
The longer the water stays in the radiator losing heat the longer it is in the block gaining heat.

[flyboyjack]

Hey guys, new thermostat. Timing is 12btdc. Didn’t have equipment to check total. But figured if there are no vacuum leaks if it’s good at 12 should be good all around. No? Im running an accel HEI. I’ll go through the pcv. Not much there but I’m appreciating all the inputs.
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[flyboyjack]

The reason I went with a high output water pump is that after installing vintage air, it would take almost no time in stop and go traffic for the temps to redline. The higher volume pump solved that issue. Didn’t figure it’d make a diff like that on the highway. Sure makes sense though.
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[weim55]

The oil consumption is not that unusual in my experience. In today’s world 110,000 miles is considered low mileage, not the case on an older non computer carbureted V8. So it’s likely the engine has significant wear. The second issue is most of these trucks come with a 3.73 gear and no overdrive. At 70 miles an hour the engine is easily 3000+ rpm and the crank case pressure will rise significantly over slow RPM use around town. Another poster is correct : make sure your PCV system is unrestricted and the filter is clean and open. But even if that is all good the system might not be able to keep up with the crank case pressure at highway speed and oil is going to get past the rings and valve guides on a worn engine.

Steve weim55 Colorado

[RichardJ]

Do I have this right? Around town mileage improved. At hwy speeds fuel consumption increased, oil consumption increased , coolant temps increased and 65-70 mph power is down. I don't like your new carb. What do the plugs look like after a hwy drive?

It's not pinging? Wouldn't hurt to check the balancer/timing mark hasn't slipped.

[Minkota]

Originally Posted by flyboyjack

Hey guys, new thermostat.
Posted via Mobile Device

I would double check the T-Stat, someone may have put the wrong one in the box. temp is usually stamped on it.

[bry593]

1. At highway speed (high rpm) fan clutch is not part of the equation. Most cooling comes from air blowing through the radiator due to speed. If radiator plugged, poor thermal transfer. Check or replace radiator.
2. If gas consumption changed at speed, maybe rpms at speed have increased. Do you have a tachometer and are the rpm's higher? Check transmission fluid level. Smell dipstick for akrid burned smell. Maybe transmission is slipping.
3. Is water level dropping? Might be a head gasket leak. Check oil for choco-milkshake appearance and bubbles in the coolant. Look for white (steam) smoke out of tailpipe. Head gaskets sometimes don't leak into oil, but may leak outside of the block. Look for puddles after you park your vehicle.

EDIT: As previously mentioned, you can test the thermostat. Simply heat a coffee mug of water in the microwave until near boiling. Drop the thermostat into the hot water. You should see it open. If it does not, it is junk.

[Steeveedee]

Running hot at speed is generally a clogged radiator, like Chevyland and bry593 mentioned. Rod the radiator or at least take it to a radiator shop to be checked for flow. The fact that it cools off in town, the only difference then is a greater load placed on the engine. A clogged radiator can cause this heating. If it's only a little, it just isn't clogged badly yet.

[cj847]

A way to check if the radiator is clogged or insufficient - when on the freeway and the motor starts to get hot, turn your heater on high. The water going thru the heater core adds capacity to the system. If the temp goes back down, get a new radiator. (in my town it is hard to find anyone to rod out a radiator - that is mainly for specialty and industrial applications now days)

[mr48chev]

Originally Posted by cj847

A way to check if the radiator is clogged or insufficient - when on the freeway and the motor starts to get hot, turn your heater on high. The water going thru the heater core adds capacity to the system. If the temp goes back down, get a new radiator. (in my town it is hard to find anyone to rod out a radiator - that is mainly for specialty and industrial applications now days)

Good suggestion right there as the heater is just a secondary radiator in the first place. I've kicked mine on in more than one rig when it started getting hot to help cool it down a tad. You have to turn the fan on too and that might not be the most comfortable inside but a little sweat never hurt anyone.

Check the radiator and condenser for bugs, dirt and crud in general on the outside. I bought an OT van a few years ago with a fried engine in it that had over half of the radiator covered with transmission fluid and then dirt stuck to it because the auxiliary cooler hose leaked. My granddad always put a piece of screenwire in front of the radiator to catch the bugs around here as the get real bad in the summer time. Then he took and washed it off when it showed that it was doing it's job.

A quick glance down the filler neck should show if you have that white crud buildup inside the radiator that is plugging the tubes up.

[mr48chev]

Just thinking, anything else you installed, left off or did that may divert air flow away from the radiator at speed? Where air being pulled in by the fan will come though the radiator at low speed if there is a path of least resistance around or over the radiator the air will take it at speed.

[LockDoc]

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Maybe I missed it but I haven't seen anything posted about a fan shroud. Do you have one?

LockDoc

[flyboyjack]

Hey guys thanks so much for your insights. I have an OEM fan shroud installed at the factory and w/o any cracks or breaking. I did just flush the radiator and clean the fins. (It wasn’t very bad). I do not have a tach, but I’ve been around engines my whole life and am as certain as I can be that the tranny is fine and not slipping. (Just put new pan gaskets in a year ago. No leaks). I am leaning towards timing and another look at the carb. I’m thinking of reinstalling the old carb after rebuilding it exactly as I find it with exact size jets, etc. I never thought about a lot of this stuff. Thank y’all so much! (P.S. no other mods or changes as I’m trying to keep this as OEM as possible).
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[geezer#99]

To save you pulling apart the carbs maybe just post the carb number for both.
We could tell you what the jets/rods should be in each.
Carb number location info here.


http://www.crankshaftcoalition.com/w...4MV_carburetor

[toolboxchev]

Been through this, it basically becomes a heat sink, sucking up more heat.

New Radiator and cooling system work that you have done will fix it. Also run it a bit richer on the carb.

Radiators will flow, with some tubes clogged. I tried to have the radiator rodded out. did not work, was clogged with tiny rust particles most likely.

[68 P.O.S.]

Manifold vacuum.....

[Molino]

Originally Posted by flyboyjack

Hey guys, ('n gals),
Here's what I've got going. All original truck with a 350/350 and 110,000 miles started running a little hot in stop and go down here in south Florida. Put in new fan clutch and high volume water pump. Flushed radiator and new coolant and "water wetter". Then replaced OEM quadrajet with professionally rebuilt q-jet. Set timing and rechecked. Tuned q-jet with vacuum gauge. The old mpg's were 10-11 around town and 14.5 to 15 on the road. Did a 400 mile road trip. Got 12 mpg! Also the truck ran warmer, (not hot), just warmer than usual. However once back in stop and go traffic, temps cooled back down to normal. (I'm estimating a 15-20 degree drop and rise). And now in my suburban driving mpg's are 13+!!! and 12 on the highway. Just again did a short jaunt on the freeway. Temps back up,...once back in the city, temps back to what I know to be normal. Also top end above 65-70 mph, power seemed to be gone and I used 1 1/2 quarts of oil in 400 miles. Again, once I'm back to suburbia, oil consumption back to 1 quart/1000 miles. Looked for vacuum leaks. Rechecked timing. HELP!!



Jack

No one mentioned it, but check that your lower radiator hose isn’t being sucked shut by the high volume water pump. The hose must be firm with the spring inside or it will get sucked closed by the water pump limiting coolant flow to the pump.

Russ

[j_cst_10]

I've had issues in the past with running hotter on the freeway and it almost always comes down to radiator capacity. Either starting to get restricted or the radiator is too small for a modified engine.

The other thing you can check is unhooking the vacuum advance and seeing if the problem still persists. The vacuum advance will add 10-15 degree of advance at light loads like you would see cruising on the freeway.

If you unhook it temporarily and it runs cooler you could be running too much total timing based on the engine combo and gasoline you use. A fix for this would be to reduce the base timing and hook it back up or buy an adjustable vacuum advance canister.

[j_cst_10]

Another thing that heats them up on the freeway is a lean condition at freeway speed. If you don't have a way to measure air fuel ratio you can put some bigger primary jets in the carb.