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Discussion Starter #1
Having trouble diagnosing an issue with my '96 HSE. It's been getting warmer than it should be lately. Head gaskets were replaced a couple years ago due to the left rear weeping coolant down the side of the block. It was slow, requiring a top off every month or so. For the last two years it's been fine.

Suddenly temps started to approach the red occasionally if sitting still or going slowly. Temps are verified with a scanner to hit around 220 max. Boiled the thermostat, full open around 185. Viscous clutch was bad, replaced, no change. It's fine driving around, but towing adds load and causes it to heat up more often. Hot wired a/c fans to run half speed, no change. The weird thing is even at 220, the clutched fan doesn't get louder like it does at first start up. It passes the newspaper test with flying colors. It seems like I'm not transferring heat to the air efficiently. I sprayed out the condenser and radiator fins even though light can be seen through them, still no change. Temps usually hover around 195 unless I try to get it hot, and then no amount of driving seems to cool it down below 212 or so, almost as if it finishes heating the water in the radiator and the radiator can't get rid of the heat. Air flow isn't the problem.

Radiator and water pump are originals at 136,000 miles. I believe one of those two is my culprit. Either the radiator has blockages or the water pump isn't flowing with enough capacity to cycle enough coolant through the radiator. Upper and lower hoses both are very similar in temperature when checked with laser probe. It's a close contact type, so I can't check across the radiator for temperature variations without sticking my hand in a fan but I'll buy one if necessary.

Sorry, lots of scattered information. Thoughts?
 

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When it starts to get hot, poke the Prog button on the HEVAC. That will set the heater on max heat and the fans on full. If the temperature drops, the radiator isn't cooling enough. As it had a problem with head gaskets in the past, did it have any leak fix gloop put in it? If it did, it is almost certainly that which has clogged the radiator.
 

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Discussion Starter #4
I'll try running the heat on full and see what happens. Good point on the stop leak, previous owner may have tried it. Think this problem would only rear it's head a couple years after all the old stuff got flushed out though?
 

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Discussion Starter #5
Got it up to 215, ran heat full blast, went up a couple degrees. Heater was blowing nice and hot. I'm at a loss here
 

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Discussion Starter #6
Alright further testing. Drained some coolant to check how the inside of the radiator looked and it looks brand new inside. Feels evenly warm after running. I was also wrong, the thermocouple on the fan is picking up heat from the radiator and properly locking up and unlocking as radiator temps rise and fall. Still, on the road with an approximately 2500 pound trailer, it gets up to 220 up hills and takes several minutes of cruising to cool back down.

Do these have plastic impeller water pumps like BMW's? I'm suspecting it's slipping on the shaft, which is why it seems like it doesn't pump any harder when the engine is revved. That or both the engine and guage sensors is reading erroneously... Iol.
 

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So if I’ve got this right, your temperature still went up a few degrees even with the heater blowers on !, I bought a 4.6 with a blocked rad, drove it home 75 miles with the heater on, but if I went over 50mph it would rise towards the red.
ive just removed a radiator from one that had some head seal gloop put in, the rad was totally blocked, visual inspection isn’t good enough, you need to check you car get a wire down each fin of the rad with top and bottom removed
 

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Discussion Starter #8
Thought about pulling the caps but I'm sure they're horribly brittle by now. The fact that the whole radiator gets hot, and the fan is picking that heat up and cycling properly is why I'm thinking it's something else where. That and the fact that this didn't progressively happen, but just sort of became a problem one day. It wasn't even over heating with the failed head gasket leaking coolant and a viscous clutch that was completely free spinning.

I did a block test and it passed that as well, as I figured since there's no coolant loss and no pressure in the tank when cold.
 

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I'd just bite the bullet and replace the water pump and radiator. Overheating is only caused b one of two things, a lack of coolant or a lack of flow. If you're not losing coolant then it has to be a lack of flow. At the age and mileage they are probably both due to be changed anyway.
 

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When the waterpump doesn't work it overheats real quick!! That's only a couple of minutes!! The V8's have metal impellars.

When the engine is at operating temperature, turn the engine off, and feel on the radiator it it;'s evenly hot all over the radiator, if there's a cool spot, your radiator needs replacing.
 

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Discussion Starter #11
I ordered a water pump since it's the cheaper of the two parts and we'll see how it goes. Obviously if the fins are full of corrosion or partially corroded away I'll know what's going on once I have the old one off.

Radiator seems consistent in temperature when heated up.

Can anyone tell me how quickly water can be seen flowing into the reservoir when running from the small diameter hose that runs from the top of the radiator? It drains into the reservoir right at the neck. Mine is a very slow weeping stream, I seem to remember it coming out much faster.
 

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Can anyone tell me how quickly water can be seen flowing into the reservoir when running from the small diameter hose that runs from the top of the radiator? It drains into the reservoir right at the neck. Mine is a very slow weeping stream, I seem to remember it coming out much faster.
Yes, it should be a constant jet of coolant. Check that it doesn't have any blockages in the pipe, the feed into the header (poke a thin piece of wire through it to check it is clear) or the nipple on the radiator. If the radiator nipple is clogged or partially clogged, that is a sure sign that the rest of the radiator is too.
 

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Discussion Starter #17
Water pump had enough play with the belt tight that the impeller had just slightly rubbed the inside of the engine. Looking at the impeller in comparison to the pump housing, the edge of the impeller almost touches the housing on one side while the other side has a substantially larger gap. I have to assume this contributes to reduced flow. New pump will go in tonight and we'll see how it goes.
 

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Discussion Starter #18
Water pump did fix the problem, hovering around 204 at idle, 194-200 while moving before topping off after it burped all the air out. Very happy it was something simple, but I'll still replace the radiator soonish because of age.
 

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I hope you have seen the posts warning against Brit part water pumps before you bought one. They have a cheap bent metal impeller instead of the cast one and the seals don't last very long.
 

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Discussion Starter #20
Came from Atlantic British. Looks identical to the old (probably not original) one with stamped impeller. Didn't want to spend big bucks on a guess.
 
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