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Getting hot at highway speeds -Solved?

AZ79K5Project

AZ79K5Project

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I’ve been chasing a gremlin that I can’t get rid of. At highway speeds - my temperature goes hot (On flat ground over a few miles at 65 mph -TBI temp at right rear of block - above 230) but cools right off at speeds below 50. I’m turning around 3000 rpm at 65 mph on days above 90 or 95 (In Phoenix)

I fairly confident that the tbi sensor is accurate. It’s back on the water jacket now and reads very close to a inferred thermometer.

Already done:
Complete flush of the system
New hoses
4 core aluminum radiator
Flex a lite electric fans (4,000 CFM) - puller
AC condenser sits in front of the radiator
Small power steering cooler for PSC also sits in front
Nothing blocking the radiator

I have a bearing noise at the front of the engine and I can’t tell if it’s the alternator or water pump
No leaks
No coolant loss
No indication of coolant in the oil

The water pump is maybe 6-8 years old, but not many miles.

stock 350 with a TBI conversion. No engine codes.

The fan had flaps that look like they’re there to let air through at higher speeds.

I feel like I’m throwing parts at the problem and don’t want to go down that insane road.

What am I missing? What should I be looking at? Is it possible for a water pump to be going bad without seepage? Should I look at the Edelbrock high performance water pump?
 
Is the radiator new? If it’s been in there a while then check the fins and see if they’re blocked by bugs or mud.
Also, since you have a hot spot on your block it sounds like you may have a air bubble trapped in your block. Forget the trick to get those out.
 
The lower radiator hose should have a spring in it to prevent it from collapsing shut at high rpms..

I've seen water pump impellers come loose from the shaft,and they fail to spin fast enough at highway speeds (might be that noise your hearing ?) ,also seen some have the blades rust away to nubs...that usually takes many years and coolant neglect though..
It could be the radiator wont allow enough flow if it is getting clogged up with deposits too as noted above..
 
New four core aluminum. I put it in after flushing and cleaning the system. The lower hose is a Gates and I don’t remember if it had a spring or not.
 
Get it up to temp and run the rpms up and watch the lower hose. I have seen this also. Make take a minute or two to start collapsing.

What thermostat are you running?
 
Good idea watching the lower hose.

I’m running a Stant 45358 - 180 degree that’s also new.
 
I don't think that it happens often, but I had a new Napa water pump on my big block that wouldn't move much coolant. I couldn't keep it cool even after trying lots of other things. I ended up getting frustrated and buying an Edelbrock pump which completely cured it. Pricey though. And the NAPA one was quiet and sealed, just didn't flow coolant enough. I had more heat in the cab with lower coolant temperatures after the swap.
I would toy with the thought of swapping the pump again after checking out the lower hose. I wonder if the impeller can't handle the elevated RPMs, or if it doesn't match the housing well.
 
I just picked up an Edelbrock pump. I’ll pull off the old pump, open it up and see what it looks like.

Is a “high flow” thermostat a gimmick or is there are legitimacy to its effectiveness?
 
The lower hose may not collapse until your going highway speeds for awhile without a spring in it,it may not do it sitting still..
A friends 455 Olds Delta 88 started overheating after he had his radiator flushed and all new hoses put on it after he bought it from an old lady and it sat almost a year,they were old and not trustworthy for road use...

We went nuts trying to fix it ourselves,he decided to buy a new water pump,which helped some,but it'd still overheat and peuke coolant when you drove it 5+ miles up the highway..tried 2 new thermostats,a 180 and a 195,same thing...
After talking with some mechanics I knew at the parts store that were customers,one of the older guys said "see if it has a spring in the lower hose--I had that happen,the new hose didn't come with one,and after I put the one out of the old hose back in it,it never overheated again"..
We drained the coolant for the 4th time and pulled the lower hose off, yup--no spring!--the garage had already thrown his old hoses away,so the mechanic installed a flexible "universal" hose with one made into the rubber for free,and that fixed it!..he said he'd never heard of this either,so we both learned something..
 
I’m thinking the new Gates hose didn’t have a spring. You used a generic lower hose?
 
High speed over heating, can be caused by the coolant moving to fast through the radiator. Also air flow though the grill can change at different speeds. Mods may contribute to this. lower hose collapsing is either a restriction from a failure, Ie thermostat, blocked radiator, or to much flow designed into water pump. How is your heater output? possibly heater circuit diverting coolant. A restriction in the heater inlet might help. I think Bob and Wade probably hit the nail on the head.
 
What kind of grille do you have ?

It is cooling at 50 so I would lean towards the air isn't getting into the radiator at faster speeds, as in not enough air flow.
 
My heater is routed off the top of the manifold to the manual heater core valve, to the heater core and back to the radiator. It’s not returning to the water pump. It seems normal, but with 100 degree temps, it’s challenging.

I did notice while looking at the system, I have fluid flow through the radiator, but it’s not flowing at the level I’d expect.
 
My friend was ready to pull the heads off his Olds,thinking it might have had a OEM steel shim head gasket that rotted enough to only let enough compression get in the system at higher rpms and foam up the coolant ,I've seen many engines with bad head gaskets that you could drive all day on back roads,but as soon as you went 65 mph on the highway a few miles it'll start overheating..many try dumping some sealer in hoping to get by for awhile,sometimes it works,but eventually the gasket leaks worse..

The mechanic who replaced his hoses used his emission test sniffer (for doing inspection stickers) to detect any combustion gases coming out of the radiator by holding the probe over the cap opening,engine running,it didn't detect any CO,so he said he doubted it was the head gaskets..
 
if you have bearing noise pull alternator take it down and have em test it you can hear the bearing when they test
if no noise bet its water pump
 
I've never understood how a cooling system pressurized to ~16PSI could collapse hoses, but maybe that's just me.

What engine did you buy the water pump for, and what fan belt setup do you have on your engine?
 
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There’s no valving to create a low pressure/high side pressure so that’s my wonder also - but I’m not a fluids expert either. I’m considering all possibilities.

The water pump I picked up is the Eldelbrock for the 79 - 350 (EDB-8811).

I’m actually using a pulley system form a Pontiac if I remember correctly that has two v-belts for the AC and power steering and a serpentine style belt for the alternator (upgraded to a three wire 120a). I added an idler pulley to increase the surface area that the belt contacts the alternator. I still have one v-belt open for the York OBA if I ever get around to it.

No reverse rotation stuff. All standard rotation.
 
Radiator cap is good?

Thermostats and radiator caps are a crap shoot anymore, for at least awhile it seemed about half out of the box, didn't work properly.

As an aside, I'd ditch the 180 thermostat at your first opportunity, and go back to a 195*. I don't see how the temp rating could be the cause, but it doesn't do TBI any favors to run that temp.
 
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