overheating?

[joshkbomb]

There is no need to pull spark plugs for a cooling system check.

Okay. In that case I'll skip the exhaust gas test since it'll cost me $8.

But, If I pressurize the cooling system and then the pressure drops (presumably because of a bad head gasket) does that mean that coolant is being forced into the combustion chamber and it would be a bad idea to start the engine?

 

[British Slave]

How does the truck run? OK? Rough?

 

[joshkbomb]

How does the truck run? OK? Rough?

It seems to run just fine. Even when the temp was reading 260+. Which is why I was originally assuming it was the gauge (well, my mechanic told me it was the gauge too). But the temperature readings on the block and the fact that burping the cooling system made it stop getting hot, leads me towards something else.

 

[British Slave]

Based on what you have said, I do not belive you have a head gasket blown. I belive you have a gauge problem, a restricted radiator, or possibly a thermostat problem. How accurate is your infrared? I have one that reads about 20* low. Your's could read high.
At this point, I would remove the thermostat and install the water neck and run it for a while to see if it runs cooler. I don't mean drive it in heavy stop and go traffic, just a short drive to let it get warmed up.

 

[Fordum]

I'd have to buy $8 worth of fluid for it, but then it would save me having to pull all the spark plugs to do the cooling system pressure test. Is this as definitive?

Do the pressure test first. Its cheap. But, you are going to put a very small amount of pressure on the system.
When a cylinder fires, there are thousands of pounds of pressure developed. A head gasket leak that passes the pressure test might still leak back the other way when the cylinder fires.

At this point, if the pressure test passes, you might want to think about the water pump.
Especially if it is still doing it when you rev it up.

BTW, the two types of blades are for the most part neither one bad. What is important is the shape of the chamber it fits in.
The one that gave me fits on the firebird, had the "good" one with the cone shaped fins, and would not pump because it did not fill the chamber.

We replaced it with the stamped sheet metal type, and it worked great. I admit the heavier the blade, the better I like them, but they have to be the right shape.

 

[British Slave]

Do the pressure test first. Its cheap. But, you are going to put a very small amount of pressure on the system.
When a cylinder fires, there are thousands of pounds of pressure developed. A head gasket leak that passes the pressure test might still leak back the other way when the cylinder fires.

At this point, if the pressure test passes, you might want to think about the water pump.
Especially if it is still doing it when you rev it up.

BTW, the two types of blades are for the most part neither one bad. What is important is the shape of the chamber it fits in.
The one that gave me fits on the firebird, had the "good" one with the cone shaped fins, and would not pump because it did not fill the chamber.

We replaced it with the stamped sheet metal type, and it worked great. I admit the heavier the blade, the better I like them, but they have to be the right shape.

Wouldn't you say he would have performance issues with a blown head gasket?

 

[Fordum]

Wouldn't you say he would have performance issues with a blown head gasket?

Blown, most definitely. Small crack, never notice, just puts exhaust gas in the coolant.

You know, just a thought, one really old school test, if you can reach the tubes through the radiator cap with your finger, wipe across them and see if they are oily.
If they are, you will get a smear on your finger.

That is a killer for heat transfer. A very fine coat of oil will cause a huge loss of cooling.

 

[British Slave]

From some 1200 miles away, I still belive it's gauge, radiator, or thermostat.

 

[4xcrazy]

I dunno, if he's been driving it when/if that block hits 260*, probably pretty well bet he has blown headgaskets and cracked heads by now.

You should definitely know if you're running that hot, at that temp it should be steaming and boiling out by then.

I ran a 305 for a very short distance once, lost all sorts of power, steam everywhere, ended up cracking both heads.

 

[dyeager535]

gauge, radiator, or thermostat.

Just my reasoning...

If his gauge was bad, his infrared wouldn't indicate there is a problem. I believe he has confirmed when gauge is reading hot, block reads hot. When gauge reads normal, block reads normal. Unlikely both infrared and gauge are malfunctioning the same way.

I kind of see where you are going on the radiator...I'm not sure if "boiling" the radiator is actually rodding, or not. I can see rodding definitely clearing out the rows (even if not as good as new) but I just don't know how effective boiling alone is. It's definitely cooling, but is the overheating because the coolant isn't moving out fast enough? What is normal temp drop across a good radiator?

Thermostat is a heck of a lot easier and cheaper to "test" by removing. I agree, instead of just replacing the water pump, you could try to run it with no thermostat. I wonder though, if the radiator is not flowing good, what will removing the thermostat (restriction) do? That *might* mask a radiator problem if there is just a bit less restriction of flow?

 

[joshkbomb]

So I think the cooling system pressure test might be a wash. I hooked the pump up around 9 and put it up to 15 psi (service manual says the system is normally <=7 psi). I stayed around for 5 minutes looking for leaks. There were a couple around the radiator hoses, but those were just initially then stopped. It was still at 15 psi, so I left it. Around 12 I decided to check on it and coolant had managed to breach the thermostat gasket and the pressure dropped down to 7-8 psi. So I'm not sure if this proved anything.

I did pressure test the radiator cap and couldn't get it to go above 10 psi more than a second (it's a 15 psi cap). Although that could just be it not sealing on the pump adapter. I have a spare radiator cap (why? I don't know) and will install it tomorrow after cleaning up and see what happens.

I think I'm going to continue on down my path of trying to rule out a head gasket leak and just do the compression test this weekend. I think it's the only way to definitively know for sure before I move on to the non-show-stopper stuff (thermostat, water pump, etc). I'm kind of curious what kind of compression levels the engine has anyway.

 

[British Slave]

Just my reasoning...

If his gauge was bad, his infrared wouldn't indicate there is a problem. I believe he has confirmed when gauge is reading hot, block reads hot. When gauge reads normal, block reads normal. Unlikely both infrared and gauge are malfunctioning the same way.

I kind of see where you are going on the radiator...I'm not sure if "boiling" the radiator is actually rodding, or not. I can see rodding definitely clearing out the rows (even if not as good as new) but I just don't know how effective boiling alone is. It's definitely cooling, but is the overheating because the coolant isn't moving out fast enough? What is normal temp drop across a good radiator?

Thermostat is a heck of a lot easier and cheaper to "test" by removing. I agree, instead of just replacing the water pump, you could try to run it with no thermostat. I wonder though, if the radiator is not flowing good, what will removing the thermostat (restriction) do? That *might* mask a radiator problem if there is just a bit less restriction of flow?

My reasoning:

Post #32

So I got the infrared thermometer and was taking temps when the gauge was reading 260+ . The thermostat housing never got above 201. That was the hottest I could find except for down near the exhaust manifold. I can't figure out how to measure the radiator except for along the side. It starts at the top near the hose in the upper 190's and drops to 125 by the bottom.

 

[British Slave]

"Boiling" the radiator will clean the fins of grease, oil, paint and dirt. Boiling is actually a chemical process, not really boiling. "Rodding" involves removing the tanks and actually running a flat rod thru the tubes to clean the inside. Most shops I have dealt with use the boiling as a first step to clean and for leak test. They plug the outlet, put a cap on it with an air line and pressure it up to see if there are bubbles in the vat.

 

[joshkbomb]

Compression test results: 120 psi every single cylinder. I'm not sure if 120 psi is enough (it's more than the service manual's minimum of 100), but I do know that if they're all the same I'm good. This means the head gasket is good?

One thing I did notice is that all the spark plugs are white on the bendable bit (ground electrode) which I think means high temps. They were light brown everywhere else. I don't think they're even at half-life yet, so I'll probably put them back in. Unfortunately I pulled the wire out of one of the boots, so now I need to get a new set of wires (they're Taylor Spiro-pro's too ).

On to the thermostat...

 

[pblaze725]

Is that radiator cap you mentioned blocking the overflow from working properly?

 

[British Slave]

Compression test results: 120 psi every single cylinder. I'm not sure if 120 psi is enough (it's more than the service manual's minimum of 100), but I do know that if they're all the same I'm good. This means the head gasket is good?

One thing I did notice is that all the spark plugs are white on the bendable bit (ground electrode) which I think means high temps. They were light brown everywhere else. I don't think they're even at half-life yet, so I'll probably put them back in. Unfortunately I pulled the wire out of one of the boots, so now I need to get a new set of wires (they're Taylor Spiro-pro's too ).

On to the thermostat...

Compression is a little low, but if it equal on all cylinders it's acceptable. Did you have the throttle open during the test? If not that may be why it is low.

 

[joshkbomb]

Compression is a little low, but if it equal on all cylinders it's acceptable. Did you have the throttle open during the test? If not that may be why it is low.

Dammit, I knew I forgot to do something. I just went out and measured a couple cylinders with the throttle open and got low 140's for both. But now the engine is cold. How important is it that the engine be warmed up?

 

[joshkbomb]

Is that radiator cap you mentioned blocking the overflow from working properly?

I'm not sure. I did notice the coolant level changing in the overflow though. Radiator caps are cheap, that one's now been replaced.

If the cap wasn't holding pressure, how would that affect the engine?

 

[British Slave]

Dammit, I knew I forgot to do something. I just went out and measured a couple cylinders with the throttle open and got low 140's for both. But now the engine is cold. How important is it that the engine be warmed up?

I would help some, but it looks like you are good to go.

 

[pblaze725]

I'm not sure. I did notice the coolant level changing in the overflow though. Radiator caps are cheap, that one's now been replaced.

If the cap wasn't holding pressure, how would that affect the engine?

I was thinking if the cap didn't let air pressure out into the overflow. Air pressure build and follow the path of least resistance back into the engine.

What temp thermostat are you using?

I looked up an '87 TBI at my local parts store and it shows 160*, 180*, and 195* but not the 220*. (CLICKY)

Maybe you have the wrong thermostat in there. IMHO I would use the one that opens the fastest.