ajd3rd

I purchased this car a short while ago. It's a 96 with 35,000 miles and had only been driven about 2,000 miles in the last 10 years. Driving it for the first time I noticed the water pump was leaking through the weep hole. I changed the water pump and the car runs at 210-215 on the highway with an outside temp of 45 degrees. Both dash gauges seem to match up in temperature and the scan tool reports the same. I thought that was too high and I noticed the lower radiator hose was cold. I changed the thermostat for the second time but that did not resolve the issue. I changed the radiator this weekend and it's still the same. The fans are programmed to turn on at 195 degrees. What I don't understand is why doesn't the lower radiator hose doesn't get hot when the temp is 210. It only seems to get hot after I shut off the car and let it sit a few minutes. I've bled the cooling system multiple times and I get just a stream of antifreeze out of it.

I really need some suggestions on what's wrong. My previous C4s have all run about 190-200 on the highway when it's 80 degrees out.
What am I missing?

c4cruiser

Sounds like an air pocket in the system. Did you open the bleed valve on the thermostat housing when you bled the system?

You can also try raising the front of the car and re-bleed the system. Starting with a cold engine, remove the pressure cap and check that the coolant level is just at the lip of the tank. Then raise the car and start the engine. Watch the coolant level as the temps rise. When the thermostat opens, you should see a drop in the coolant level in the tank. Raise the engine RPM to around 1100-1200 and add coolant up to the lip on the tank (you are using DexCool, right??). Replace the cap, shut the engine down and let everything cool down to about 100 degrees or so. Take the car for a short drive and watch the temps.

A temp of 210-215 is not that bad as the C4 is designed to run a little warmer that other cars. That is primarily for reducing emissions. You did check the radiator and A/C condenser for any debris that would bloxk airflow? While it's important that air can easily pass thru those components, the cold lower hose is indicative of an air pocket.

don hall

That is the temp your vette should be running now.

Did you replace the t-stat with a proper LT1 t-stat?

Have you monitored the flow of coolant during operation...ie:
as the engine heats does the expanded coolant flow into the overflow
bottle, and during cool-down, does the coolant siphon back into the reservoir?

If not, there is air entering the closed system via a deformed radiator cap gasket, split or loose hose ends, etc.

ajd3rd

C4cruiser thanks for the reply. I did open the bleeder multiple times but maybe it is an air pocket. I've also driven it multiple times with no improvement. Hopefully I'll have time tonight to jack it up as high as possible, run it and see if I can get anymore dexcool into it.

don hall

There is no need to bleed the LT1 engine, as it is self-bleeding. If there is air in the system, it will flow into the reservoir, as it is positioned at the highest point in the engine compartment.

I'm aware of the bleed screws, and I have read most of the posts describing gigantic bubbles. I owned a '93 for 12 years, and a '92 for 4 years, so I have some experience with the LT1 engine. Before I was made aware the LT1 was self-bleeding, I bled my '93 after a coolant change, and only a few bubbles appeared. The size of the bubbles was the size of the bleed valve orifice.....about 1/8". So much for gigantic bubbles.

If the cooling system is full, you have either an air flow problem, or a coolant flow problem, or both.

You might find this an interesting read:

http://www.corvetteactioncenter.com/...ystem-526.html

bac22

Unless I'm missing something, that's the normal operating temp of LT1/LT4. You can modify that if you like
http://tech.corvettecentral.com/2011...modifications/

ajd3rd

Seabright, thanks for the reply. I did replace the stat with the correct LT1 type. As far as coolant flow, the lower radiator hose does not get hot while the engine is running so I assume the thermostat is not opening and also there is no change in the overflow tank. I'm wondering if the previous post is the issue where there is an air pocket in the block preventing the thermostat from opening. I'll try jacking the car and bleeding it again. Any other ideas are greatly appreciated.

don hall

Expanded coolant (hot engine) will be forced out of the block. If it is not flowing into the over-flow bottle, then I'm thinking that the system is not full of coolant. You can't change the laws of physics.

don hall

Something to consider..... since the vette has been not operated very much in the last 10 years, there may be a build up of sediment in the bottom of the block.

You might consider a coolant system flush. A proper flush requires the removal of the 2 knock sensors located in the bottom of the block.
Removing the 2 sensors, and allowing coolant to flow to ground is not sufficient to remove years of sediment. You need to inject water under pressure into the sensor holes to dislodge the sediment. There are "L" shaped nozzles that will fit into the sensor holes.

It is recommended to replace the knock sensors with new.

ajd3rd

Thanks to everyone for the replies. After reading the attached articles and posts I'm thinking the system is not full. I'll try jacking it and running it since I've already tried driving it and the thermostat doesn't seem to open until the car is shut down and the heat builds up. Maybe it's air bound and therefore not opening. Worst case I'll pull the thermostat and see if I can manually fill up the block. I'll post an update once I try running it again to see if it will take any more dexcool.

hcbph

Here's an old trick that works on some vehicles that are air locked. Find yourself a parking ramp with as steep of inclines as you can find. Turn the heater on full, low gear and go up in low with rpm's up. With luck it will push any air in the engine or heater through to the radiator. Once done, insure the overflow is full so it will draw it back in. Had a Chevelle that was the only way to get all the air out, but it worked.

ajd3rd

hcbph,

Thanks! I hope to try jacking it up so it's on an incline tonight.

belairbrian

Keep in mind out heater cores are always flowing
turning heat to max just moves the blend air door
it will tell you if there is flow through the core but doesn't open a valve in the cooling system

ajd3rd

Today I had a little time. I jacked up the car and ran it with the cap off. I got a little more Dexcool in it but not much. Ran it on the highway for about a half hour and it ran 208-210. I also have a 95 Coupe with 19,000 miles on it all original I purchased new. I drove that on the same route it ran 188-190. I went over the car again and it seems it's not holding the coolant system pressure. I'm thinking it could be one of a few problems. The ugly ones: head gasket or heater core. The easy one radiator cap. The hoses are in good shape and I checked all of the clamps and they seem tight. Do you think a bad radiator cap could make the system run hotter?

Thanks!

don hall

Assuming the cooling systems are equal......no air or liquid blockage.... the 2 vettes should run the same temp.

Did you monitor the flow of coolant to and from the overflow bottle in both vettes? Expanded coolant will flow into the overflow bottle. The cap has a measuring gage attached. When hot, coolant should be at, or above the "hot" level. After cool-down, the coolant will be at, or below the "cold" level.
If the cap doesn't have a gage, the bottle should have "hot" and "cold" marks.

This is called a "closed" system. No outside air enters the system.
If it does, there is a breach allowing air in, and no return siphon will occur.

Without a return siphon, and you don't add coolant, the radiator will always be low on coolant. Low coolant means eventual higher temps.

As we discussed, the rad cap just controls pressure. A 15# cap will raise the boiling point about 50 deg. preventing steam to form.
Any deformity with the cap gasket will cause an air leak.

don hall

Have you inspected the front air dams? A deformed dam will prevent air from being directed to the radiator. That is just as important as debris removal from the fins.

don hall

Review my post #9....."flush".

1800Wing

The cheapest part of the system will always cause the most problems...when I changed my water pump. optispark and all the hoses I also replaced both radiator caps. Took about 4 cycles of running the engine till the fans came on...shutting it down.. and bleeding the system from the bleed screw on the thermostat housing. No problems so far.

later, tiny

don hall

Tiny, I'm easily confused, so please help me understand. You changed the opti so that means you own a '92-'96 vette. You "replaced both radiator caps". I'm only aware of one rad cap which is on the reservoir. And you bled the system from the bleed screw on the t-stat housing. Not aware of a bleed screw on the t-stat housing.

1800Wing

The primary radiator cap and the one on the tank on the passenger side near the firewall. I'll see if I can find the pictures I took during the replacement.