BarretHC1

Hello fellow C3 brothers and sisters. I am having 2 issue going on that I can not figure out. The first is, overheating. This is overheating NOT at idle. I can start my car and let it run for hours, and it stays right around 180*. If I drive it for a decent amount of time, the gauge creeps up to 210 and will probably go higher. I aim my temp gun at the block (area just above where water pump would be) and its 240* on the digital display. It also boiled off some coolant when i shut the vehicle off, out of the reservoir tank hose. Iv'e replaced my thermostat and much of the coolant. Any ideas?

Now, the bigger concern.. The car's drivetrain runs AWESOME when cold. I open her up, she sounds beautiful, drives perfect.... When she gets hot, I have an issue. So, when she gets warm, and I turn left or right and down shift, or stop and back up, or stop and go forward, I get a shudder/feels like somethings slipping from the rear end. Almost feels as if the wheel(s) is/are slipping. I can feel it under my drivers seat (like a vibration and a shudder/chatter/slipping, and sometimes a bang when it catches when I rev it). No noise is associated with this. No grinding, or squealing etc....

Maybe a bearing, or spindle, or pressure plate, or rear end? maybe something with the slip differential, or even clutch or pressure plate? I don't feel like it's the clutch or pressure plate because I can also feel it if I manually turn/push the rear drivers (and presumably passenger wheel too- but I never push it in on that side) when its in neutral to push the vehicle back into the garage. So it happens under load, whether mechanical or by me pushing back the vehicle at the tire. It disappears when I put the clutch in and also if its doing it and I give it more gas, but will come back shortly (but only when hot).

HeadsU.P.

Overheating at idle, is a air circulation issue.
Overheating at speed, is a water circulation issue.

So, you are not getting enough coolant around to where it needs to go. A common problem at speed is the lower radiator hose collapsing. This restricts flow, is impossible to see happening and usually fixes itself in stop & go traffic. Your 240* is not acceptable. I would recommend grabbing the lower rad hose and see if you can feel a spring in there. Some old springs weaken and just corrode away. Newer hoses have re-enforcement built in. Or I should say, out-side of hose.

Next: condition of the Rad itself? When idling with the Rad cap off, does coolant appear to be circulating across the top of the rad?

Waterpump capacity: The pump itself seldom goes bad but if the fan belt has continual slippage . . . . . . .

Thermostat. Not likely. You say runs cooler at idle. Possible blockage in thermo if really old, but I doubt it.

sug

Do you have ac and have you changed your diff oil and not used the posi additive.

BarretHC1

I had replaced the thermostat so its not old, but I will check the hose and check the radiator reservoir with cap off. I was initially thinking fan clutch or water pump, but the more people I talk to seem to think its not that because they don't fail often. Could be a blockage... Or, I could've installed a gym thermostat I suppose..

BarretHC1

I do not have AC and I have not changed the oil myself, Iv'e owned the vehicle for only 3-4 months, and have been going through it fixing and making little things right. These are the last 2 bigger items. My mechanic did say the rear end was overfilled, and took some diff oil out (let it drain even to the plug). I am not sure about post additive though... It's something to look into. Maybe without the additive I'm getting slippage in the rear end which is what it feels like.

BarretHC1

I am going to look into another new Thermostat, and possibly a new water pump. Also, I'm going to check the posi pressure plates in the rear end. I can't think of it being anything else logically. Thanks guys!

calwldlife

symptoms of a cracked head or intake gasket or rust/scale
sorry.
pull spark plgs and maybe one or two will be steamed cleaned

HeadsU.P.

Maybe, but I don't think so. OP says it boiled over coolant, out the overflow tube, but no loss of coolant into the engine. If it was a cracked head, the coolant level would recede and be burned off. Intake gasket leaking would also drop the coolant level.
The rust / scale has some possibility though.

blue by you

for the slippage, you need to drain the rear and put in new gear
fluid and 2 bottles of GM posi fluid then go do some slow figure
8's in a parking lot to get the clutches well lubed.

BarretHC1

That is what I'm going to try this weekend. If that doesn't solve the issue, I'll report back. In regard to the heating issue, I'm thinking radiator and coolant flush, maybe just throw in a new radiator too....

NewbVetteGuy

Great post, HeadsU.P.!

-I wondered what the heck that spring was doing in there; it's just in there to stop the hose from collapsing?!? Wow. Learned something today.


Adam

NewbVetteGuy

Guys on the overheating under power issue, could this just be the Dexcool sludge issue preventing the cooling system from working properly? (with far less HP at idle, it might cool fine despite all the sludge and then when he's actually producing a good # of BTUs, the cooling system just is too inefficient with the sludge?

-I just realized this was the cause of MY cooling issues, which also didn't show up at idle. (It's easy enough to drain like 1/2 a gallon of coolant and look at the exposed fins in the top of the radiator to see if they're all crusted up and then go the radiator flush route, if they are.)


Adam

calwldlife

steamed plugs is a long shot.
true that clean plugs would mean coolant use/loss/

my guess stems from seeing a bad head gasket that held under coolant pressure and cylinder vacuum but allowed air to be pumped into the coolant when cyl was under compression.

i hope it is crud/rust.
a goo flush will be better than gasket repair.
it is amazong how much crap an engine can have in the coolant system