LUVTruck.com

Aloha everyone, again! My truck is overheating intermittently, mostly when I'm driving at highway speeds, and then when I idle, the temp drops back down to normal. I drained the coolant (which was mostly water) and refilled it with a new mixture of 70/30 coolant/water, and it doesn't spike up as quickly as it used to, temperature wise, but it still will peg the H. Before draining it, it would go past it.

I took off the bottom radiator hose, did the water trick, and it spilled out immediately, the flow didn't slow down, just stopped abruptly. I'm assuming that means the radiator isn't plugged. I do have a semi-new radiator cap (4 years), which I'm going to replace, and I'm not sure if the thermostat is old, or if it was replaced when my dad and I did the rebuild back in 2008. There's no leaks, the oil isn't milk chocolate, and there's no foam anywhere, so I'm hoping it's not the head gasket! I've replaced that damn thing 3 times now.

Any other tips you guru's could come up with?

Thanks!

edit:: I have the type of radiator cap that you can pull a lever and it releases the pressure. When I release the pressure when it's pegged at h, it seems like the temp drops immediately back to normal operating temp.

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Been reading other topics, and want to know if someone can post pictures, or tell me what I should be looking for if I want to flush the entire system? I don't mind losing 8 bucks of coolant if it means fixing the problem. I've read you take off hoses, put a garden hose in it, and flush it out until the water is clear. The heater core and the radiator.

Anyone care to explain how to do this? Is there anyway to do it wrong...? Because I'll just go out there and do it now lol.

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Sounds like it could be a sticking thermostat. If you are ready to drain everything anyway you might as well replace it too. Fairly cheap and fairly quick to replace. If you fill up the cooling system through the thermostat hole, then install the t-stat and top hose, then top off the rest of the system at the radiator, there should be minimal amounts of air in the system when you start it back up. You still want to watch to make sure the new t-stat opens once the motor warms up, the top radiator hose should suddenly get hot. An air bubble trapped right at the t-stat will keep it from opening.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

So I can tell when it opens up when the top radiator hose suddenly gets hot? I thought about pulling off the thermostat and filling it up that way but already filled it back up, and of course it still over heats while driving. I'll go back out there and open it up, and look at it.

Thanks!

If I've already filled it up, could I just pull the thermostat off, fill it up a little bit, and replace it? to ensure there's no air?

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Water goes up through the t-stat into the upper radiator hose only after it opens, so it will stay coolish. When the t-stat opens you can feel the temperature on that hose rise very obviously and pretty fast. I actually have a small infrared thermometer that I will sometimes use to test the opening temps of the t-stat. Pointed at the t-stat cover the thermometer will climb fast and level off at just around the temp the t-stat opened at.

If you just pull the thermostat cover it will of course drain out all over but only down to the level of the t-stat, and then you can replace it and refill just what is missing. I did this on my 86 Trooper last summer (almost identical t-stat placement) and even managed to catch most all of the coolant in a couple drain pans instead of it leaking all over the ground. Remember that stuff is poisonous.

Make sure it is good and cold when you open it up, and you could drain a little out of the radiator drain before you open it to avoid as much spillage.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

I'm trying to catch as much as I can, have a few bowls and pans lying around... I'm headed to pick up a new thermostat right now at the parts store, and will replace it once the truck cools down.
Thanks for all the info 800xl I'll let you know what happens once I get it replaced.

should I bother with any type of sealant for the thermostat? Or just use the gasket?

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I use a thin coat of blue silicon on both sides of my gaskets. It doesn't take much.

I always test my thermostats in a pan of boiling water before installing them,even if they are new.
I once went through 3 stats that were new but defective.

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"You can't please everyone,so you've got to please yourself"

ll do this boiling water trick as well.
I've got some of this so I'll put it around it. For the thermostat it doesn't have to be just red silicone? but can be blue?




Bought the new one, waiting for the truck to cool down and then I'll tear it apart. I'll try this boiling water trick while I wait.

On a side note, the truck doesn't get all the way hot now, at least according to the gauge, but gets to right before the H, maybe about 1/2 cm or so. Hopefully replacing the thermostat will fix this problem.

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any luck

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Luvless
1980 Mikado-Sold.

1993 Lexus SC400 my Daily
2004 Yamaha WR250F my new love in life
2016 Toyota Camry my girls ride

nada. replaced it, managed to snap off a bolt head but luckily was able to get it out with vise grips. lol. I mean, it doesn't get to ALL the way hot, or even "--" <---that close to it, if that made any sense at all. but it's still over heating according to the gauge. I don't smell anything, it doesn't seem like it's over heating, but I want to ensure I do everything I can.

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sooo... when installing the thermostat, I didn't check when I pulled the old one out, which side goes into the manifold? the side with the spring/coil? or the other shorter/stubbier side?


edit.. google searched. sorry for my dumbness. gonna ensure I did it the right way now. lol

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sorry for the triple post, but I just discovered that the bottom hose on the radiator is cold. The top is hot. This means there's a circulation issue right? Could it be the water pump.. or what's going on? I'm going to remove the hose and check for blockage, because when I was putting water in the radiator, it spilled out of the bottom of it radiator without an issue. That bottom hose should be hot as well, right?


EDIT:

all hoses are hot now, but still overheating. slower, but still gets up there in temp. I got them all hot by squeezing them over and over again (dunno if this really helped. ha), and keeping the radiator cap off to try and get all the air out. Heaters blow hot air fine as well.


edit 2: it seems the bottom hose only gets hot if I squeeze it when initially starting the truck, otherwise it remains cold.

I'm starting to think it's the radiator. I thought my dad had had it re cored and everything when we did the rebuild. We just painted it apparently. I'm wondering about the water pump too.

Got a local quote and it's 135 to recore the radiator and clean it out. Finding a radiator online is even worse, 200-400. I was hoping it would only be like 50-70 dollars to clear it out and recore it.

Anyone got a non clogged luv radiator you wanna sell!?? lol

could I get away with purchasing a gallon or w/e of radiator flush fluid and giving it a try?

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I think if it was my truck...I would get some cooling system flush.Put it it and run the truck until it gets hot.Take off the upper heater hose,radiator cap and hook a garden hose to it.Let the water run until the water comes out clean.I would put the old thermostat back in before I did this as well.

Maybe suspect the gauge or sending unit. Maybe check the temp with a handheld infrared thermometer. You know, the ones RC guys use. Hobby stores sell them.

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OK, I'm over it. Where's the beer?

What is your timing set at? I bought a LUV with a overheating problem and it turned out the timing was retarded, set timing to specs and it ran fine.

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Certified pilots, looking down on people since 1903.

I have a timing light so I'll check it out tomorrow. If it wasn't in time, wouldn't it run horribly?

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My dad was telling me the same thing. I'll go pick one up in a couple days.

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It depends on how retarded you are...

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If you think no one cares, try missing a couple of payments...



FIAA!

SFPP!

From reading all your symtoms here I believe you will find a clogged radiator. You have good heat from your heater correct? This means the water pump is circulating the water correctly so you can eliminate that. The top hose is hot but the bottom one is cold means that after the thermostat opens the water is not circulating through the radiator fast enough or at all.
Same thing going down the road at highway speeds. The engine is making more heat and the clogged radiator can't get rid of it fast enough.
On a normally working radiator the top hose should be hot and the the bottom one should also be quite hot but much less so. This means good circulation.