L31MaxExpress
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Yea the 8.1 is a Gen6.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.
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Yea the 8.1 is a Gen6.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.
Should be gen 7.Yea the 8.1 is a Gen6.
Should be gen 7.
Late 7.4 and 8.0 were gen 6
Not exactly.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.
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.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.