Why get hot over miles?!?!

[Tom Bryant]

I've seen that happen before too. Have you checked the radiator for bubbles when this happens? If it's pushing air into the cooling system I'd think it might bubble in the overflow tank so you wouldn't have to risk removing the cap. When the electric fans are running all of that air flow would be going through the radiator. By all means replace the foam seals around the radiator be be sure that all cooling air passes through the core. Your water pump should be ok if it isn't leaking. I suppose that the blades on the impeller could corrode away enough to reduce water circulation. You would have to take off the rear cover to see that. Zip has a rebuilt kit if you would want to do it yourself. It isn't hard. All you need is a shop press.

Did you have the block bored when you rebuilt the engine? It could be that you are transferring more heat into the cooling system than you were with the thicker cylinder walls before boring.

Tom

 

[GerryLP]

Scott and Tom,

Exactly my fears as well. But I'm checking the simple stuff first because more often than not, is. The radiator had three hairline cracks and two tubes nicked. Plus, there was always a quarter-sized puddle in the garage after parking Gail in it overnight, from a leaking drain plug. They all got fixed.

I am planning to remove intake (get TDC set up), and investigate the backfiring to make sure that the intake gaskets are not leaking.

On the head gasket suggestion, one telltale sign is missing, though. There is no water in the engine oil and no oil in the radiator water. The engine has 0.015" thick copper gaskets, so not impossible to have a leak, but they are pretty reliable for they are one piece.

Nevertheless, the "might-as-well" rules still apply.

 

[geekinavette]

Scott and Tom,

On the head gasket suggestion, one telltale sign is missing, though. There is no water in the engine oil and no oil in the radiator water.

Doesn't matter...a combustion chamber-to-coolant system leak can easily NOT end up with coolant in the oil (or oil in coolant).

Bill

 

[GerryLP]

Doesn't matter...a combustion chamber-to-coolant system leak can easily NOT end up with coolant in the oil (or oil in coolant).

Bill

Perhaps. That would suck, though. I spent good money for the heads to get reworked and pressure tested before installing. :ugh

However, the overheating takes place overtime. On an open road. Around town, it runs fine. It is a puzzle for sure.

 

[Tom Bryant]

A crack or other leak that would only open up after a long period of heat soaking would explain why you can drive for hours before it becomes a problem. This may be really hard to detect. The bad part is with every hopeful fix you do a 4 to 6 hour run is required to be sure you fixed it. Before taking the heads off why not pressurize Each cylinder with an adapter like you would use in the spark plug hole to hold the valves closed for changing springs and watch for bubbles in the radiator? Go up to 200psi or more to see if you can force the issue. I'd try this after a long run to get the iron up to operating temps. I would think that by using more cylinder pressure than normal you should get some leakage through a crack that may not open enough under compression pressure until it has heat soaked for hours.

Just a thought and it might avoid taking the engine apart.

Tom

 

[GerryLP]

A crack or other leak that would only open up after a long period of heat soaking would explain why you can drive for hours before it becomes a problem. This may be really hard to detect. The bad part is with every hopeful fix you do a 4 to 6 hour run is required to be sure you fixed it. Before taking the heads off why not pressurize Each cylinder with an adapter like you would use in the spark plug hole to hold the valves closed for changing springs and watch for bubbles in the radiator? Go up to 200psi or more to see if you can force the issue. I'd try this after a long run to get the iron up to operating temps. I would think that by using more cylinder pressure than normal you should get some leakage through a crack that may not open enough under compression pressure until it has heat soaked for hours.

Just a thought and it might avoid taking the engine apart.

Tom

Im not too worried about it. I'll cross that bridge when I get to it. I'll make sure the cooling system is GTG and that no vacuum leak is causing the motor to work harder than it should. If the next long distance trip reveals the problem again, then we'll know that the heads are next.

 

[Peer81]

Hello Gerry,

I've read everything but it is something weird! My question is, what is the oil temperature doing up to the 4 to 6 hours and after that?
What speeds are you driving? In my opinion if you have a 200F tempature for coolant and oil then that is how hot the engine is and that is it. No way if all the other things are stable that something in the engine thinks oow crap let me get hotter just for the fun of it!?

If I drive for 10 minutes or longer at speeds between 100 to 110 mph then the coolant stays perfectly at 180F but the oil gets hotter and hotter 200, 220, 240. So maybe the oil temp is creeping up very slightly and that could trigger the crack in the head to open. But than again, if the coolant gets hotter then hot gas should be entering the coolant system as the exhaust pressure is higher then the coolant pressure. But when you shot it down at this high temperature then the exhaust pressure is zero, coolant gravity is higher so coolant should go into the cylinder? Only if you let it cool first and then shot it down (so the crack is closed) you don't have this problem. We all know the late C3 heads aren't the best to say the least the only way to know for sure is to x-ray the heads or magnaflow them.

Greetings Peter

 

[GerryLP]

Hello Gerry,

I've read everything but it is something weird! My question is, what is the oil temperature doing up to the 4 to 6 hours and after that?
What speeds are you driving? In my opinion if you have a 200F tempature for coolant and oil then that is how hot the engine is and that is it. No way if all the other things are stable that something in the engine thinks oow crap let me get hotter just for the fun of it!?

If I drive for 10 minutes or longer at speeds between 100 to 110 mph then the coolant stays perfectly at 180F but the oil gets hotter and hotter 200, 220, 240. So maybe the oil temp is creeping up very slightly and that could trigger the crack in the head to open. But than again, if the coolant gets hotter then hot gas should be entering the coolant system as the exhaust pressure is higher then the coolant pressure. But when you shot it down at this high temperature then the exhaust pressure is zero, coolant gravity is higher so coolant should go into the cylinder? Only if you let it cool first and then shot it down (so the crack is closed) you don't have this problem. We all know the late C3 heads aren't the best to say the least the only way to know for sure is to x-ray the heads or magnaflow them.

Greetings Peter

Peter,

I think the reason this condition appears,"weird", is because it is likely a combination of issues. I mean, they did find three cracks on the solder joining the upper & lower tubes, and left tank to the core. On top of that, a couple of nicks on two tubes which leaked very little, and did not leave easily recognizable traces.

But to answer you question, the oil temperature gauge helped me monitor the engine closely. I used it to help me determine if I should just pull over right there on the freeway, or if I could afford to slow down and take the next exits with services. The radiator was never completely empty. Some water managed to flow (the water going to the engine being picked up by the bottom tube), so the problem was obviously the remaining water not being sufficient to sustain the freeway speeds. The oil temperature gauge was routinely about the middle of the gauge (oil pressure gauge was normal given the high flow oil pump I used on the motor), and everytime oil temperature would creep up, I would slow down. Sometimes even to 35 MPH, until I got to the exit close to services.

The heads were magna fluxed and pressure checked before install. Of course, that only tells you they were not cracked upon installation. I am not discounting what you guys are saying, and thank you very much for the helpful suggestions and discussion, but I am not going to throw myself in a complete engine tear down based on suspicion alone. And by the way, a vacuum leak together with a leaking radiator could cause it as well, for a vacuum leak makes an engine work harder, just as I feel that the fan clutch being bad was also helping the problem manifest itself sooner. The process of elimination will reveal it sooner or later.

 

[Peer81]

Hello Gerry,

You're right, start with the radiator when you know that is oke then move to the next thing if coolant keeps disapearing.

Groeten Peter

 

[Hib Halverson]

Ok.
I've been reading this thread for some time.

Two things which no one has really addressed are sticking out and that is the engine "backfiring" and the drivability going away when the ECT gets hot.

For now I'm going to rule out a cracked head because person who started the thread says he had the heads mag'ed and pressure tested. I'm also going to rule out a leak in the cooling system because the OP says the car runs fine for hours on the highway at high speed.

I see this car is an 81. Do you have a scan tester which supports the 81 system? If so and that tester can read the data stream while your driving, put the tester in the car for the next trip and when the ECT starts up take a look at spark timing and the oxygen sensor. If you see retarded spark or the engine running lean, both of which could cause ECT to rise at highway speeds, your problem may not be only with the cooling system. You may have some kind of problem with engine controls.

 

[GerryLP]

Peter, we have been having almost monsoonal conditions the last three weeks, so I have not been able to continue with the Vette.

Last Sunday, the sun came out for a couple of hours (of course, good weather seems to be most predominant when I have to be at work lol), and i surveyed the engine bay. I'll be honest...I knew I didn't have enough time to mess with the car at that time, but for a moment I thought it best to skip the intake exploration and just install the radiator to make another drive test. If I mess with the intake and the problem goes away, then I would end up with a best guess as to what fixed it, if indeed the problem would get fixed. Then, another part of me thinks that it would suck to spend the summer troubleshooting the problem one-change-at-a-time. I guess I need to take the sensible road, and attempt to fix the problem one-change-a-time. It that even makes sense. Hahaha :L

Hib, I have been able to adapt a vacuum gauge to monitor vacuum while driving the car or even a dwell gauge to see how the fuel metering is doing while cruising, but what scanner I could borrow to indeed monitor the engine while driving?? Do you guys know of any? I'm seriously considering this idea.

Also, I may be borrowing a Borescope from work to inspect the intake runners to see if there is oil cocking build-up on the valves, indicating a gasket leak on the intake.

 

[Hib Halverson]

I don't know of any consumer scan tester in the market these days which supports the 81 system.

You'll need to look for some really old stuff. It's been too long for me to remember what popular-priced testers were available back then and which supported the 81 system.

As for pro-grade equipment either a TECH1 or TECH1A, both of which are out of production but available on the used market, and when equipped with GM Powertrain software and a 12-pin to 5-pin DLC adapter will work.

Also, the Bosch Mastertech with GM Powertrain software and the 12-to-5-pin adapter will work.

If you were closer to where I'm at, I'd gladly loan you my Mastertech.

You can read the O2S output with a DMM.

 

[GerryLP]

I don't know of any consumer scan tester in the market these days which supports the 81 system.

You'll need to look for some really old stuff. It's been too long for me to remember what popular-priced testers were available back then and which supported the 81 system.

As for pro-grade equipment either a TECH1 or TECH1A, both of which are out of production but available on the used market, and when equipped with GM Powertrain software and a 12-pin to 5-pin DLC adapter will work.

Also, the Bosch Mastertech with GM Powertrain software and the 12-to-5-pin adapter will work.

If you were closer to where I'm at, I'd gladly loan you my Mastertech.

You can read the O2S output with a DMM.

Thanks for the information, Hib. I will have to learn from square one about these and the equipment required.

I woke up today to T-storms, so I spent a couple of hours straightening fins on the radiator. :ugh

 

[GerryLP]

Started re-installing the radiator back into place. I covered the heat exchanger areas with cardboard, to minimize the damage to the fins during installation. You either remove half of the pulleys and belts, and air pump, and you wont need to protect the fins as much, or you protect them. The fan shroud, as you all know, is very clunky and massive and with limited movement. The bottom hose tube on the radiator was another problem. In my case, it seemed to help to lower the radiator into place with the top tube on radiator oriented to the top, and the bottom tube oriented to the bottom. Once i cleared the right upper control arm (A-arm) hinge bolt, then I rotated the radiator into position. The seals make it harder, of course. I just took my time.

The assembly book only shows the relative positioning of the radiator seals, so this are the problems I found once I installed the upper short sections.

1) Replacement seals are longer than factory ones
2) The positioning shown in the assembly manual does not show (nor warns) about the upper holding brackets interfering with the seals, and vice-versa.
3) The vertical seals actually seal between the radiator tanks (left and right ends of radiators) and the support frame.

The left side (and by the way, the factory ones seemed more crooked than these).

The right side (notice that the distance between the tank's seem (marked by the bottom cushion in which the seem sits) is about 3-1/2" over to the right, thus the seal also sits that far.

The holes you see at the top end of the seals on the frame are the bolt holes for the upper radiator holding brackets. So the seals must stay away from these.

I forgot to take pictures of the radiator in place with the upper holding brackets installed. I'll take those when I get back on to the project. until then...

 

[Peer81]

Great reply Gerry! Lets hope this was the problem but you need some good weather and some hours to drive to find out. Keep us updated.

Greetings Peter

 

[GerryLP]

Ok, so I was able to start the Vette today. The transmission cooling line adapters for the radiator were worn, so I made new ones. Installed the fan, the pulleys, and AC compressor.

Found an old factory marking under the dirt for the upper air damn duct. It says March 9, 81. I am not sure what the "-30B" means.

The radiator is connected except for the upper radiator hose.

I have yet to install the upper seals. The only thing that leaked was a short piece of hose that connects an additional transmission oil cooler. I called it a day.

 

[bill81vette]

Gerry, -30B meant the coolant was good to 30 below zero...

 

[GerryLP]

Gerry, -30B meant the coolant was good to 30 below zero...

Really? Wow! I do learn everyday. Lol

 

[GerryLP]

Engine running (short run; not to operating temperature). It only leaked at the transmission cooling line. Fixed that today.

Microsoft services

 

[GerryLP]

Test run day

Hello folks,

I finally got Gail ready for her test run. Installed everything except for the seals that channel the air to the air intake duct. Those came without the adhesive backing, so I have to get glue for them.

here is the first video...

https://youtu.be/3Z2duecCkRA

after approximately 100 miles of driving at freeway speeds.

https://youtu.be/ZhjNILJjAvk

and this one is about a couple of miles from the Tucumcari exit. The other way, there was a huge backup thanks to an 18-wheeler's wreck (luckily no one died). I stopped over at the Kix on 66 restaurant to enjoy the day (95 Deg F but nice in the shade), and wait for the backup to dissipate.

https://youtu.be/z2Xeti9lXJI

ill post another video, showing what it does with the A-C turned on.