InfernalVortex

iTrader: (4)

The car always runs cool. Normally it goes up to 190 and then the thermostat opens and it runs closer to 160-170 the rest of the day. (The temp sender for the gauge is, obviously, down in the cylinder head, farther away from the thermostat... )

but the other day it climbed up to 240. I pulled over for a minute. Let it cool and cranked it back up and it ran at 160 the rest of the drive home.

I replaced the thermostat and the radiator cap to be sure there was nothing fishy going on but it seems to have gotten worse. It will overheat idling.

Fan is running, water pump turning. Coolant system has pressure, and boiling water is getting into the overflow tank.

Im thinking one of those really low temp days back in November might have gotten to it. I had a tester that said it was good for 10 degrees last spring. I added more antifreeze to the mix back then just for the sake of a little extra margin since temps just dont get that low here in central georgia very often.

So Im a little confused... but Im not really seeing any other possibilities beyond there being something off internally. All the plugs looked okay at first glance, and there's no steam out of the tail pipe... yet. Oil looks fine too. But the coolant shouldnt be boiling over. I'm really feeling like there's no other explanation beyond a structural failure inside the engine.

I had a pressure tester on it, but I dont really trust it very much as I had coolant leaking back up through the tester when I used it. But for whatever it's worth, it showed that the system was NOT holding pressure. But I cant be sure if that's a leak inside the tester or not.

RamIt

A mild head gasket leak or cracked head could push combustion gasses into the cooling system displacing water causing it to run hot. You really need to get a working pressure tester to verify it can hold cap pressure over an extended time.

91 1LE

iTrader: (1)

Sounds like your thermostat stuck causing the overheating. Your issues now lead me to believe the overheat blew one or both of your head gaskets, cracked a head, etc. Are you sure the bubbling in your overflow is boiling coolant and not exhaust gases? I've had that happen before.

InfernalVortex

iTrader: (4)

Yeah but I pulled over before it got into the red zone on the gauge... It never got over 240. And it was fine the rest of the night. Im not compeltely opposed to that being the case, but I kind of feel like whatever problem was there is the same one that is there now judging by the way it's acting.

And am I sure it's boiling coolant? No, not at all. Not really sure of any good way to check. I flushed that system several times but the milkshake from the previous engine 7 years ago left a certain amount of residue in the radiator, so the coolant has always smelled a little off. So it smells the same as ever.

But I will say I could feel bubbling in the upper rad hose the other day when the temps were fluctuating from 240 to 140. When I finally shut it off it was around 200-210 and I could still feel bubbling in the upper rad hose then.

Thermostat->head gasket is definitely possible, and Im starting to think it's a best case scenario at this point, honestly.

Will a compression test be definitive to establishing this?

91 1LE

iTrader: (1)

Using the factory gauge to determine the actual temp is a bad idea. They are notoriously inaccurate.

A compression test is a good way to find a blown head gasket/cracked head. Sometimes the spark plugs are a tip-off if one or two of them are considerably cleaner than the others. This indicates water in the cylinders.

The "boiling" coming from inside the engine is what makes me think it's the head gasket(s). A properly operating cooling system raises the boiling point of coolant with pressure so it doesn't boil inside the engine. I suspect your "boiling" is actually combustion pressure entering the cooling system. You can test for this specifically with whats called a "block sniffer." It uses a chemical that reacts to the presence of hydrocarbons (exhaust) in the cooling system.

InfernalVortex

iTrader: (4)

Something just doesnt seem right...

I've driven it a couple more times since then. Gets up to temp as slow as ever. If I drive it around the block, it will quickly climb to 230-240F. If I shut the car off for 30 seconds or so, it's back at 160F.

Certainly none of these are showing any symptoms of a head gasket leak.



I tried to do a compression test, but the header primaries are in the way of the tester. I got numbers 1 and 3 done before I gave up and decided I was going to have to pull the exhaust off the car to finish the job.

Either way, I was happy to see that number 1 and number 3 show teh same readings, so whatever that oil sludge on the number 3 plug ( 2 4 6 8 7 5 3 1 is the order in the picture from left to right) doesnt seem to be connected to the rings...

You'd think if a head gasket was going or there was a crack in something, that at least one of these plugs would show it, right? The oil looks fantastic. There's definitely no water in the crankcase. I did see small particles in the radiator, but they seem to be from the overflow tank, which has a scum ring at the water level... which I feel indicates something, but Im not quite sure what. Just like the radiator cap had some spoogey mucus on it when I pulled it the other day. Maybe that's head gasket.... I dont know.

I did run it with the cap off (Before it was up to temp, obviously) and had a buddy watch for bubbles escaping, but we didnt see any evidence of that. I did see occasional black flecks of... wahtever, in it. THat could be normal. I didnt see enough of it to think it's necessarily an indicator of anything.

Ozz1967

iTrader: (4)

Your'e not loosing any coolant are you?

The headgasket leak may also be to the outside, not internal. It's a small posibility, but with everything else you've checked, i'm not sure where else to go.

How old is your water pump? It's possible it's going bad internally...I've read about that happening, usually on original or old pumps though.

Another thing could be your lower hose is collapsing, but usually that is only found at higher RPM's.

The last thing I can think of, is sludge inside the motor that's not coming out. Perhaps running a good flush/cleaner through the block would help?

naf

iTrader: (7)

Vortec manifold gaskets are very prone to leaks unless you used the new style with the metal reinforcements and torqued to spec (11 ft lb). The issues are all over the truck boards.

The leaks usually allow coolant to seep into the front intake ports but oil can pass as well. This maybe what has discolored your plugs? Usually the leaks result in loss of coolant and overheating is a secondary issue if the level gets too low. May not be your problem but if those gaskets have been on for several years...

InfernalVortex

iTrader: (4)

Coolant always evaporates in this car. It's got that vented overflow cap, so it will just evaporate off. I put maybe a pint in it a year. I dont really think much of it. Theres always water in the overflow tank.

Water pump is from 2009 when I put it together.

That is a VERY interesting point about the leak of oil into the intake port. Sseems like a probable cause of the ugly plug. It's a shame it doesnt keep it from overheating.

The other week when it did it, I shut it down for a minute and it was immediately back to normal temps and stayed at 160 all the way home. That was at least 5 or 6 miles of highway driving there where it was fine.

I guess Im just going to have to bite the bullet and get another coolant system pressure tester from a different place and get the exhaust off and do a pressure test on each cylinder.

But I kind of feel like if there's a crack in a head or a leak in the head gasket, that if it's not bad enough to show up at idle or to show up on plugs, then it's not going to show up on a compression test either. It needs to be under load to build up enough heat.

Maybe it IS clogged up somehow... but I dont know that would happen.

The belt is off right now, and the water pump turns smoothly. No wobble in the pulley. No water out of the weep hole. Has smooth resistance. Plus I could see the coolant moving when the cap was off the other day. So I think the water pump is fine.

I guess Im just back to square one. Compression test and pressure test with a tester that works properly.

1. Radiator cap IS new.
2. Fan IS running
3. Plugs look normal
4. Overheats under load
5. Thermostat is new and IS opening.
6. Pump appears to be functioning normally.

This only leaves bad things....

naf

iTrader: (7)

Just ensure you take proper precautions after completing your pressure test. You don't want to break a starter nose (I have) or worse...

naf

iTrader: (7)

another note: no change in mileage or trouble codes? any loss of power when it overheats?

InfernalVortex

iTrader: (4)

This is a carbureted car. So no codes or anything would be happening.

BTW I finished my compression test a few minutes ago. Every single cylinder is between 180 and 190. Im a little surprised given how gunky that spark plug is on number 3, but that makes me think yall are right on about that intake gasket.

But this doesnt solve the overheating issue.

There are no coolant leaks on the ground ,and no noticeable coolant loss either.

How can I tell if the radiator is clogged? Is that something that can happen?

Bob88GTA

iTrader: (2)

"How can I tell if the radiator is clogged? Is that something that can happen?"

Been following Infernal. I chased similar issues on my 88 that I bought new years ago. Turns out it was the radiator was pretty bad off.
I took it out and went to a rad shop. They took the ends off and rodded the passages in the entire radiator. Boiled it out, put new end tanks on, and wella. Stamped that puppy done! Never had an issue since. Just keep the antifreeze in it nice.

Just a thought

Bob

Justin@Entropy

If you can rule out the head gasket, sounds like you have a sticking thermostat, a bad water pump/slipping belt or the radiator is done.


Assuming the head gasket is OK, If I were to guess based on what you said, the water pump may be the culprit here.


What about yanking the rocker arms and doing a pressure test?

Ozz1967

iTrader: (4)

I think Boib88GTA hit it on the head here. You've ruled out just about everything else. Unless the waterpump is "bad", but not totally toast and still able to move some water.

The only way I know to check a radiator is to pull it and have a shop work on it. Sorry I haven't been more help.

InfernalVortex

iTrader: (4)

Well you guys are taking stabs in the dark, I dont expect miracles, just a little direction.

Before I flush or take anything off the car, i decided to go grab a pressure tester from a different store in the hope sthat it would work properly.

I accidentally slightly over-pressurized the system to 16 psi. It dropped to 15psi 5 minutes later. So I let it sit another 20 minutes and it stayed stable at 15psi. I *THINK* that is a pass. I've never done it before, and all people say is to "do the test"... The cap is only rated for 15... I figure that 1 psi might just be air getting past that seal on the tester. Or the gauge on the tester, whatever. I think 15 psi for 15 minutes steady is a good sign.

Any of you guys with more experience on that have anything to add?

Water pump is going to come off next and Im going to disassemble it to check the impeller. If that looks fine I'll replace the rad and rad hoses.

I just dont see how a water pump could fail so... suddenly and intermittently like that and still feel fine. You'd think there would be a gradual loss of cooling performance with any of the remaining possibilities, though. I kinda wish I had a friend check that lower radiator hose, now. This radiator has served me really well. It's a 3 row replacement radiator and I think it's the main reason the car has always run so exceptionally cool. Even with the 195 T-stat it always runs at 170F, and I can see the temp climb to 190 (CTS is on the head, t-stat is at the top, so I presume its still a cooler reading regardless) and then drop back to 160-170 and hover even in hte middle of georgia summer with a single stock RS radiator fan on it.

InfernalVortex

iTrader: (4)

do you guys think a leak down test would be necessary to rule out cracked heads?

Water pump impeller looks fine. bearing feels fine. It's a little gross but I see nothing to indicate it's not functioning well.

Im not going to be happy until I find a cause. I refuse to throw parts at it unless I can find a problem.

RamIt

I dont understand how the engine can run under the thermostat opening temp unless it's defective.

I like your idea of not throwing parts at it.
A small crack can allow combustion gasses to enter the cooling system. Think of the cylinder pressure after it lights off. It can be well over 1000 psi.
Napa has a kit to check for the presence of combustion gasses in the cooling system.

If I was in your shoes I would bite the $50 bullet and get the kit just for the peace of mind that cracks or head gaskets were not the problem.

InfernalVortex

iTrader: (4)

Thermostat is in the top of the engine.

CTS going to the gauge is in the side of the head much farther "upstream". That's how I always figured. If it didnt go up to thermostat temp before dropping I would just assume it was off by some amount, but it will get up to thermostat temp.

I need to find one of these testers somewhere. I will note however, that just by the human sniff test, the coolant looks and smells very normal.

Is it possible for the radiator hoses to collapse at 2000 RPM?

91 1LE

iTrader: (1)

The fact that the temps drop back to normal so quickly indicates either a thermostat issue or an air pocket in the engine. If the entire engine and all of the coolant were at the overheat temp it would take a considerable amount of time to cool to normal levels. Are you still using the stock temp gauge? If so, you may have no issues at all except a typical GM temp gauge. A small hole drilled in your thermostat will help alleviate an air pocket under the thermostat. Air trapped underneath will not allow the thermostat to open as it can't sense coolant temp through the air.

InfernalVortex

iTrader: (4)

Even though the coolant temperature sensor for the gauge is way down low in the side of the cylinder head and I can feel the upper rad hose is warm?

I gotta admit, some of what you're saying makes a lot of sense. Where should I drill this hole? I've never drilled a thermostat before. I thought I remembered reading that they allow a certain amount of bypass normally. Is that not true? I tried to give myself a little bit of breathing room between teh water level in the intake and my RTV when I put this new thermostat in. There's no way the water was all the way up to the level of the thermostat when I sealed it up. So it definitely would have had an air pocket there. But I figured it would take care of itself through teh overflow tank and running it a little while and cooalnt flowing around etc. I've never had issues with air pockets before, but I havent replaced that many thermostats in my time either. The last couple of times I did I always refilled the manifold all the way up to the thermostat line. And this time I just got lazy....

I will say something that struck me as very odd that 've been trying to figure out for a few days now is the other day when I was messing with it, I was trying to feel for bubbles in the upper rad hose, and my other buddy was like "this doesnt even feel THAT hot, not like the gauge is saying, anyway..." and I said "yeah, but you can feel the air bubbles in it..." So I had my OTHER buddy shut it down while we were both feeling the hose, and immediately as soon as we shut it off, the hose got VERY hot, to the point that within a few seconds we couldnt keep our hands on it.

My buddy thought that since the coolant stopped flowing, it began to transfer heat to the hose as it was just sitting in the hose instead of moving. But something about that explanation doesnt feel right to me, and Im not sure if it's a clue or not.

Ozz1967

iTrader: (4)

Based on what you just said, this last part about the hose getting hot. You could have an intermittently sticking thermostat. Usually they stick "open", but yours might be sticking closed occasionally.

InfernalVortex

iTrader: (4)

I just boiled the thermostat... it opens... closes when I take it out of the wate,r then reopens when I put it in. It did have a chunk of silicone in it somehow, but it didnt seem to affect things. I pulled it out after my test. I do wonder if maybe there was some large air pocket near it that caused it to shut,a nd every time I would move the car, coolant slosh and open it. But then it would slosh away and it would close. But arent the overflow tanks and so on pretty good about eliminating air pockets? The engine should suck coolant in as it burps air pockets out, right? How hard is it for the pump to push water up to the thermostat if there's a pocket there? It would certainly explain why under load it would warm up very quickly, since I'd be going forward and sloshing coolant away from the thermostat.

Im installing with the spring facing down into the engine, Im pretty sure that's correct, but I just wanted to check in case I missed something obvious.

I still think if the head gasket was bad or the head(s) were cracked I'd be able to smell gasoline/exhaust in the coolant. I did with my first 350 that milkshaked on me... What do you guys think?

Im thining about getting one of those funnel things and running it with the cap off and seeing when the air in the system comes out and how long it does it. If that is inconclusive I'm goign to have to borrow a sniffer test. But I've got to get some RTV and some gaskets and get everything put back together, probably wont be til next week. :-\


1. Lower rad hose could be collapsing. I need to check for this.
2. Thermostat could have stuck shut the first time it overheated, it was fine afterwards, but I replaced the thermostat to be safe. I may have left a large air pocket in there, leading to the problem significantly worsening.
3. Radiator is clogged (any good way to test for this? I dont see mcuh of anything alarming in the coolant. No "dirt" or anythingl ike that.
4. Head gasket is allowing exhaust gasses in, but not liquid out. I presume all head gasket failures start like this.

naf

iTrader: (7)

Drill a small hole in the flange of the tstat, 1/4" is fine. Just big enough to allow any air trapped underneath to pass. Otherwise I think you're fine.

91 1LE

iTrader: (1)

Drill the thermostat as stated above, reinstall it, top off your radiator and do the following.

Start with a completely cold engine, radiator and overflow full, and radiator cap OFF.
Start engine and let it idle. Look into the radiator and pay close attention to what you see. If everything is normal the only thing that should happen is the water level MAY drop. You should not see water moving in the radiator. As the engine idles, squeeze the upper radiator hose. It should be soft and cool. Keep an eye on your temp gauge as the engine warms up. When it reaches the thermostat opening temp the following will happen: The water level in the radiator MAY drop, the upper hose will get warm, and you should see water movement in the top of the radiator. Top off the radiator with water and now install the radiator cap. As the engine continues to run, the upper hose should get hot and will get harder to squeeze due to pressure.
Now that the engine is warm and still running and the thermostat is open do the following:
Observe the lower radiator hose. It should be round, obviously. Now rev the engine while watching the lower hose. It may move slightly but make sure it doesn't go flat/collapse.
After you confirm the lower hose is ok, squeeze the upper hose again (careful, it will be HOT) and as you release it you should feel the water forcing it's way through. This is a rudimentary test to make sure the water pump has adequate flow/pressure.

Note any variations from what is described above (bubbles, flow, no flow, etc) and we will go from there.

RamIt

It wouldn't hurt to fill and burp the system with the front end jacked up in the air too.
The top of the radiator is too close to the top of the engine on these cars.

InfernalVortex

iTrader: (4)

Thanks guys! i'll have updates in a couple of days.

InfernalVortex

iTrader: (4)

Hole in the thermostat worked apparently. It took quite a while to get it up to temperature, but as soon as it did it went back down to 160 and stayed. I drove it about 30 minutes today trying not to wander too far from home. Couldnt get it on the highway, but so far, so good. Guess it was air pockets, which means it was probably a sticking thermostat the very first time it overheated.

Ozz1967

iTrader: (4)

Glad you figured it out!

NCC-2569

iTrader: (1)