1998 k2500 454 getting hot

[454cid]

Would you have a flap and a hose? What I'm getting at is has OP made his truck not factory with respect to bypasses.

I believe the BBC has used a bypass hose from the very beginning.... Mk1 W engines. I don't know what you've got for a thermostat.... is it something you looked up by year/make/model? Maybe it's something Whipple specified?

There are people that try to do without the bypass hose, but it usually doesn't work, as far as I know, without purposeful modifications or uses. This is why I asked earlier if maybe the OP still had it functioning. You can buy a molded hose for it, but I usually use a piece of straight bulk hose. If not done carefully, it could kink on the underside, and possibly not flow well enough..... OP should check this, now that I think about it. The trick is that it needs to be just the right length. Long enough to fit onto both hose barbs, but not so long that it kinks in the middle. Next time I do mine, I have a piece of silicone heater hose for it.

I typically rotate the hose after I get it onto both barbs, so any kinking gets taken out.

 

[df2x4]

I have nothing useful to add, but would like to thank Supercharged111 for the new addition to my mechanical vocabulary. (Flappydoodle)

 

[Supercharged111]

I have nothing useful to add, but would like to thank Supercharged111 for the new addition to my mechanical vocabulary. (Flappydoodle)

I can't take all the credit. Also not sure if this link is gonna work.

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[Erik the Awful]

Glad I used the high flow water pump

I'm not a fan of high flow water pumps. This is a case of "more is not always better". I know we're dealing with trucks and high rpm is not as much of an issue for us, but in engines that are geared toward high rpm use, you can cavitate your water pump. In other words your pump draws out of the return hose so fast that the pressure drops enough for the coolant to boil in the hose, and then your water pump can't pump until the coolant changes back into a liquid. You'll get a big temperature spike for about five to ten seconds. You have to pair the high-flow pump with a smaller diameter crank pulley, which basically makes it back into a standard volume pump.

 

[newguyinnc]

Filling in some blanks here...

There are two coolant circuits to consider, and one pump.

The first circuit is within the engine (and heater, if equipped). When the thermostat's closed, the pump circulates coolant within the engine circuit, where "higher flow" promotes more temperature uniformity wherever the coolant flows (block, heads, intake,... heater). I assume the OE pump design / operating RPM is adequate to meet GM's design objectives for temperature uniformity. However, a "higher flow" pump will reduce whatever non-uniformities exist in this circuit.

The second circuit is through the radiator and flow in this circuit is gated by the thermostat. The thermostat is immersed in and registers the temperature of the engine coolant circuit and, when the engine circuit's temperature exceeds the thermostat's rating, the thermostat opens and allows coolant to flow, as it exits the engine's circuit, through the radiator's circuit where it exchanges heat with the air, lowering the coolant's temperature before it returns to the pump.

The issue in the OP's case seems to be that the ENGINE doesn't have uniform temperature throughout. Increasing the flow in the engine circuit will make the temperatures more uniform, more-or-less regardless of the thermostat's operation.

In all cases, the pump's total output is directed into the engine circuit. What varies is the source of the pump's input, which depends on the thermostat. Thermostat closed: All input to the pump comes from the engine circuit. Thermostat open: The pump's input is a mix of flow from the radiator circuit and the engine circuit.

I know a lot gets forgot after the feed gets pages long. I bought the truck and noticed bringing it home 45 minute drive on the highway the truck ran considerably warmer on the gauge (around 220°) than my other big block truck. Changed coolant sensor for gauge. No change. Changed water pump and 195° thermostat. No change. Changed fan clutch. No change. After 50 miles, hub came off of new water mump and sent fan into radiator. Started from scratch with new factory 3 core radiator meant for truck, new 195° thermostat, new fan clutch, new water pump, new a/c condenser, new upper and lower radiator hoses. No change. Had catalytic converters checked. No change. Threw my hands in the air and had motor completely rebuilt at a highly reputable machine shop. No change. After motor was rebuilt the coolant was vacuum filled. Changed to 4 core aluminum radiator. No change. Timing on this motor is spot on zero with the scanner. We noticed the long term fuel trim looked bad and changed injectors and regulator. No change. Next step is mechanic is taking the ECU out of my other truck and swapping them to see if that's the issue. Computer doesn't seem to be doing what it should with total advance at speed. Any suggestions would be greatly appreciated. I'm too deep in this truck at this point to walk away from it. When we changed to the 4 core radiator, I had bought an Edelbrock water pump supposed to be meant for this truck and neither of the bolt patterns on the hub matched up with my pulley and fan clutch.

 

[newguyinnc]

The original bypass hose for the water pump was in good shape and reused. Other than the new 4 core aluminum radiator, everything is factory spec new. Mechanic hot wired the electric aux fan to be key on hot and it brought the temps down about 10° , but still doing the same thing. Running the truck empty with no load runs 215° down the highway, pull off and it creeps up to about 225° within 10-15 seconds. Get it moving again and drops back to 215°. With a load (empty dump trailer) runs at around 215-220° and when stopped at a light hits 235 ° on the gauge. Double checked dash gauge with mechanical gauge in same location in the head and the dash gauge is spot on. ECU sensor when the dash gauge says 235° says 203°.

 

[newguyinnc]

Filling in some blanks here...

There are two coolant circuits to consider, and one pump.

The first circuit is within the engine (and heater, if equipped). When the thermostat's closed, the pump circulates coolant within the engine circuit, where "higher flow" promotes more temperature uniformity wherever the coolant flows (block, heads, intake,... heater). I assume the OE pump design / operating RPM is adequate to meet GM's design objectives for temperature uniformity. However, a "higher flow" pump will reduce whatever non-uniformities exist in this circuit.

The second circuit is through the radiator and flow in this circuit is gated by the thermostat. The thermostat is immersed in and registers the temperature of the engine coolant circuit and, when the engine circuit's temperature exceeds the thermostat's rating, the thermostat opens and allows coolant to flow, as it exits the engine's circuit, through the radiator's circuit where it exchanges heat with the air, lowering the coolant's temperature before it returns to the pump.

The issue in the OP's case seems to be that the ENGINE doesn't have uniform temperature throughout. Increasing the flow in the engine circuit will make the temperatures more uniform, more-or-less regardless of the thermostat's operation.

In all cases, the pump's total output is directed into the engine circuit. What varies is the source of the pump's input, which depends on the thermostat. Thermostat closed: All input to the pump comes from the engine circuit. Thermostat open: The pump's input is a mix of flow from the radiator circuit and the engine circuit.

This sounds like what I have going on is non uniformity it my engine cooling circuit. With the engine being freshly rebuilt, could this be a fully/partially blocked heater core causing the reduced flow through the engine circuit? The problem persists even after the thermostat starts cycling.

 

[Supercharged111]

The original bypass hose for the water pump was in good shape and reused. Other than the new 4 core aluminum radiator, everything is factory spec new. Mechanic hot wired the electric aux fan to be key on hot and it brought the temps down about 10° , but still doing the same thing. Running the truck empty with no load runs 215° down the highway, pull off and it creeps up to about 225° within 10-15 seconds. Get it moving again and drops back to 215°. With a load (empty dump trailer) runs at around 215-220° and when stopped at a light hits 235 ° on the gauge. Double checked dash gauge with mechanical gauge in same location in the head and the dash gauge is spot on. ECU sensor when the dash gauge says 235° says 203°.

Where did you get this "4 core" radiator? I believe it was already mentioned, but a true 4 core aluminum radiator would be worthless. Where aluminum shines is it's strength over copper/brass. Aluminum does not conduct heat as well as copper brass, so making a radiator with 4 small cores will make it less effective at cooling than a 4 core copper/brass. Copper/brass used 4 cores because the material is weak, so the cores can only be 1/2"-5/8" or so max before they run the risk of bursting. Aluminum being stronger can support core sizes of 1"+ per, and those larger cores are able to shed more heat than 2 smaller copper/brass cores could given the same area. My stock dually radiator is a 2 core, but it's just as thick as an old school 4 core radiator and the truck does not overheat. I wonder, if you truly do have a 4 core aluminum unit, if you wouldn't be better served by a parts store 2 core unit.

 

[newguyinnc]

Where did you get this "4 core" radiator? I believe it was already mentioned, but a true 4 core aluminum radiator would be worthless. Where aluminum shines is it's strength over copper/brass. Aluminum does not conduct heat as well as copper brass, so making a radiator with 4 small cores will make it less effective at cooling than a 4 core copper/brass. Copper/brass used 4 cores because the material is weak, so the cores can only be 1/2"-5/8" or so max before they run the risk of bursting. Aluminum being stronger can support core sizes of 1"+ per, and those larger cores are able to shed more heat than 2 smaller copper/brass cores could given the same area. My stock dually radiator is a 2 core, but it's just as thick as an old school 4 core radiator and the truck does not overheat. I wonder, if you truly do have a 4 core aluminum unit, if you wouldn't be better served by a parts store 2 core unit.

The aluminum 4 core I put in it is an alloy works specifically designed for that truck. Before the aluminum 4 core, I had a brand new factory 3 core in it. Even the factory 3 core is aluminum core with plastic tanks. That still doesn't explain why my temps are 30° different from the middle of the driver's side head and the intake manifold. For some reason, coolant is not a uniform temperature between the block, heads, intake and heater core. When temp at the ECU sending unit below the thermostat is 200°, the gauge says 230-235° when the truck isn't moving. Have verified several times that the dash gauge is reading correctly.

 

[Supercharged111]

Nope, that definitely doesn't explain it, but just to be a stickler for terminology factory used 1 core and 2 core back in 98. No 3 core.