1998 k2500 454 getting hot

[L31MaxExpress]

I think you're thinking of the 8.1l gen vii head bolt pattern.

Cooling passages are all that I think are different prior to that. Oiling for the blocks.

Yea the 8.1 is a Gen6.

 

[yevgenievich]

Yea the 8.1 is a Gen6.

Should be gen 7.
Late 7.4 and 8.0 were gen 6

 

[Supercharged111]

Should be gen 7.
Late 7.4 and 8.0 were gen 6

This.

 

[1998crewcab]

Not all thermostats are the same
High flow ac delco on top
original type replacement gm ac delco on bottom
High flow pump push around 20 percent more coolant, like having your truck rev 20 percent faster
i don't dog my truck so having cavitation problems at 8000 rpm
is not an issue ...

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[Schurkey]

Late to the thread but there are two different styles of big block cooling passageways through the deck surface and matching gaskets. Mark VI vs Gen 5. Gen 6 is all together different but the head bolt pattern is different.

Not exactly.

The Mark IV started out with series-flow cooling. Water enters the front of the block from the water pump. Flows around cylinders to rear of block, through two large holes in the rear of the block, head gasket, and head. Coolant flows forward through head to intake manifold crossover, thermostat, and out to the radiator. The coolest coolant in the engine--entering the block from the water pump, is directly below the hottest coolant in the engine--leaving the cylinder head for the intake manifold.

SOME Mark IV, and ALL Gen 5 and Gen 6 engine have parallel-flow cooling. Head gaskets for Gen 5 and 6 are all parallel-flow, but head gaskets for Mark IV can be either series or parallel, or a hermaphrodite combination. Water enters front of block from water pump. Some portion of the coolant gushes up to the head through passages in block, gasket, and head between first two cylinders, some portion of the coolant gushes up to the head between the middle two cylinders, some portion of the coolant gushes up to the head between the rear two cylinders. All the rest enters the head at the rear of the block like the series-cooled engines. Many (not all) parallel-flow head gaskets are restricted at the rear opening.

The difference is the head gasket and the three holes in the block decks (six holes total.) ALL the heads, back to '65, have the holes for parallel cooling even when used with series cooling.

Drilling the block deck holes, and using the correct gasket can change a block from series to parallel flow. Parallel flow is very slightly preferred as it keeps coolant temps more even throughout the block.

If a person uses a parallel-flow head gasket with restricted rear coolant passage on a block that doesn't have the additional parallel-flow holes between the cylinders, it'll overheat and there's NOTHING that will fix it until the head gasket is replaced, or the missing parallel-flow holes drilled.

Keep in mind that the engine in question is a '98, therefore it's a Gen 6, therefore it's parallel-flow, and all the Gen 5 and 6 head gaskets are parallel-flow. You'd normally expect the most-even coolant temperatures throughout the engine with parallel-flow. There's another difference in the head gaskets between Mark IV and Gen 5, at the front. I can't remember how the Gen 6 gaskets are set up.

As said, the Gen 7 8.1L had a slightly-altered head bolt pattern (and different cooling system holes in the block/gasket/head.) Three head bolt holes in each deck surface were moved; and not very far--"about" half the diameter of the bolt. The Mark IV, Gen 5 and Gen 6 head-bolt patterns are identical.






I'll be shocked if another water pump makes any difference.

I think the original poster should put masking tape over the gauge. The temps are perfectly normal at the thermostat and the sensor for the computer. I don't think there's a problem to be fixed. The gauge sensor is picking up heat from the exhaust. I might verify those things that might lead to an extra-hot exhaust--ignition timing advance, fuel trims, and restricted exhaust flow, though.

True enough, I can't replicate that gauge problem on my '97; but I also don't work it very hard.

 

[Supercharged111]

Mine will show 210 when the PCM shows 220, but it doesn't jump when I stop. This was 20k GCW in 100 degree heat in my dually. My Camaro's FSM states that the gauge will read 210 until about 220 or 225. Can the OP try another cluster? Swap them between trucks?

 

[BeXtreme]

Maybe throw one of those spark plug insulating sleeves over your coolant temp sensor in the head to see if it makes any difference?

 

[newguyinnc]

If my temps on the gauge were staying consistent when I pull off a highway I wouldn't think twice about it. I fully understand no 2 engines are exactly the same even if built with identical parts, but the 20-25° jump just by pulling off the highway tells me coolant isn't properly circulating through the engine circuit. I did take a look at the bypass hose today and although it's not linked, it does look to me like it's too long and has an upward angle in the intake which may be restricting flow. Had the mechanic order a new one today. Outside of that, we're still looking into if I have a lean condition. The engine builder I used is the most reputable around here , so I highly doubt the wrong head gaskets were used, especially since the motor was doing the exact same thing before it was rebuilt and had never been apart before this. At this point, I honestly don't think there's one thing to point to. I think it's several small things that are contributing to one noticeable problem. Once he gets everything back together and driveable again, we gonna go for a drive with the mechanic in the passenger seat with live data and see what everything is doing.

 

[newguyinnc]

Not exactly.

The Mark IV started out with series-flow cooling. Water enters the front of the block from the water pump. Flows around cylinders to rear of block, through two large holes in the rear of the block, head gasket, and head. Coolant flows forward through head to intake manifold crossover, thermostat, and out to the radiator. The coolest coolant in the engine--entering the block from the water pump, is directly below the hottest coolant in the engine--leaving the cylinder head for the intake manifold.

SOME Mark IV, and ALL Gen 5 and Gen 6 engine have parallel-flow cooling. Head gaskets for Gen 5 and 6 are all parallel-flow, but head gaskets for Mark IV can be either series or parallel, or a hermaphrodite combination. Water enters front of block from water pump. Some portion of the coolant gushes up to the head through passages in block, gasket, and head between first two cylinders, some portion of the coolant gushes up to the head between the middle two cylinders, some portion of the coolant gushes up to the head between the rear two cylinders. All the rest enters the head at the rear of the block like the series-cooled engines. Many (not all) parallel-flow head gaskets are restricted at the rear opening.

The difference is the head gasket and the three holes in the block decks (six holes total.) ALL the heads, back to '65, have the holes for parallel cooling even when used with series cooling.

Drilling the block deck holes, and using the correct gasket can change a block from series to parallel flow. Parallel flow is very slightly preferred as it keeps coolant temps more even throughout the block.

If a person uses a parallel-flow head gasket with restricted rear coolant passage on a block that doesn't have the additional parallel-flow holes between the cylinders, it'll overheat and there's NOTHING that will fix it until the head gasket is replaced, or the missing parallel-flow holes drilled.

Keep in mind that the engine in question is a '98, therefore it's a Gen 6, therefore it's parallel-flow, and all the Gen 5 and 6 head gaskets are parallel-flow. You'd normally expect the most-even coolant temperatures throughout the engine with parallel-flow. There's another difference in the head gaskets between Mark IV and Gen 5, at the front. I can't remember how the Gen 6 gaskets are set up.

As said, the Gen 7 8.1L had a slightly-altered head bolt pattern (and different cooling system holes in the block/gasket/head.) Three head bolt holes in each deck surface were moved; and not very far--"about" half the diameter of the bolt. The Mark IV, Gen 5 and Gen 6 head-bolt patterns are identical.






I'll be shocked if another water pump makes any difference.

I think the original poster should put masking tape over the gauge. The temps are perfectly normal at the thermostat and the sensor for the computer. I don't think there's a problem to be fixed. The gauge sensor is picking up heat from the exhaust. I might verify those things that might lead to an extra-hot exhaust--ignition timing advance, fuel trims, and restricted exhaust flow, though.

True enough, I can't replicate that gauge problem on my '97; but I also don't work it very hard.

We've already cut the exhaust free , it's not back pressure. Changed injectors because of bad long term fuel trim numbers. The only thing we can find is it doesn't seem to stay in advance the way it should, but I can't see where that would cause a 20-25° jump from highway speed to coming to a stop at the offramp. 215° on the highway, pull off and come to the stop sign, 225°. Cross over the overpass to head back the other way and stop on the side of the on ramp and in 5-10 seconds it'll be reading 235°. Rev it or take back off again it'll drop back to 215° in a few seconds.

 

[454cid]

For the bypass, I find that a piece of straight bulk hose works well.