I have a 70 Camaro with a 454 in it. When I bought it in March I discovered that the wire was off of the sending unit. When I would connect it and run it the gauge went to redline pretty much immediately. I quickly replaced the aftermarket NAPA sending unit with a correct one from Letric Limited. I also tested the sender and verified that it read accurately with the gauge when boiled in water. I still noticed that when I ran my car at idle it will run at about 210 all day long (180 thermostat). As soon as I pull it out of the driveway the temp went up. So I watched more closely to find that when it idles it is at 210 but as soon as I give it throttle it will go up. Now this is either driving or just revving it in the driveway. I took the cap off and ran the car to operating temp. Observing the coolant showed that when I rev the motor I get a few bubbles. Then it looked like the thermostat opened and I got several bubbles. I did a compression test on the cylinders and all were the same. I threw a pressure tester on the radiator. I ran it to temp and it never got higher than 7psi. Then I shut it off and pumped it to 15 and it held fine. Also, when I pulled all the plugs they appeared to be a tanish color. None appears to have been steam cleaned...

Appears your cooling system is simply not able to throw off all the heat your engine is making.

First things first, check your timing, and crank in as much initial as she will stand, that will help her run cooler.

Problem is probably flow rate, either a bad water pump (corroded impeller) or restricted radiator.

Appears your cooling system is simply not able to throw off all the heat your engine is making.

First things first, check your timing, and crank in as much initial as she will stand, that will help her run cooler.

Problem is probably flow rate, make sure you are using a high flow thermostat (richardson or mr gasket) it's probably either a bad water pump (corroded impeller) or restricted radiator.

Jim, I was told that the radiator was recored when the car was restored. Not many miles on this motor... Think water pump might be a good first try. Also, I did put a new 180 thermo in it but it was from NAPA. I will go and grab a Mr. Gasket 4364 to drop in. Man I want to fix this problem before summer is over.. Thanks for the advice.

First things first. Have you shot the thermstat housing with an IR gun to make sure the temperature reading you are getting is correct..or in the ballpark? And, where is your sensor?...head...intake?

I would definitely do the chemical strip test in the cooling media for combustion by-products. While bubbles themselves are not necessarily a definitive indicator of issues with the heads... it could be a factor.

Next, typically systems that run up in temperature with the provision of throttle could be due to several factors. First, take the thermostat OUT...and see if the temperature still exhibits this behaviour. It could be a faulty thermostat closing under flow. Or...a bottom hose collapsing under flow (this should be able to be seen). Also, is your exhaust plugged for some reason? This willdrive temps up quickly. How good is the radiator?

How hot does it get just driving down the road at 55+mph. This should be about the lowest temperature.

I have access to an IF temp gun so I will hopefully give that a try tonight.

The sensor is in the head.

Is the strip test an over the counter thing or do I need to take coolant to a radiator shop?

The muffler theory is interesting. When I bought the car (in March) one of the mufflers what bad. Seemed like a baffle went and eventually it blew a hole thru. I had that one replaced then the other side went bad but never blew a hole thru the muffler. Now I have 2 new mufflers.

When cruising down the road the car will get to the tip of the redline. Which mush be about 225 or close to 230. Throttle off and it goes right back to the 210 area.

I think the lower hose collapse can be rulled out as I have revved the engine and held the hose. Haven't noticed any...

I will also try to run without a thermo...

Thanks much for the replies...

Bubbles...indicates head gasket...INDICATES...run a radiator CO/hydrocarbon test

As Steptoe suggests, bubbles indicate head gasket. I would adapt the compression tester for use as a cylinder filling device with shop air and pump in a min of 100PSI and check rad cap for bubbles. Or bubbles indicate cavitation at the pump. You must get each cylinder up to TDC and at operating temp.

A high flow thermostat, ie, MRG-4364, might help. I'm sure shroud, fan blades, and radiator are all in good shape. Radiator is of the proper size?

I'm surprise it only pressurized to 7 PSI with 230*F. Usually, with this high of temp, heat soak will push the temp up and if one listens carefully, you can hear the coolant boiling in the block, just as a pan of water boils on the stove. Higher coolant system pressure is needed to prevent this event. This is why I run a 22 lb cap on the radiator on my 454 TBI dually. Is your cap in good shape?

With the IR gun, measure the inlet tank and outlet tank temps. There should be a min of 20*F differential. The more the better.

The air drawn across the radiator should feel very hot. If not, either rad is restricted, but you said its been tended to, feel the core of rad with hand to find cooler spots, of course after engine is turned off, or the fan isn't pulling air like it should, either wrong blade pitch, or fan clutch is worn out. Most BBC's cam with fan clutches. Or maybe the pulley is of the wrong size. Most AC equipped engines have a 30% larger crank pulley to speed up pump speed.

As said before, exhaust restrictions can contribute to extra heat. If you still have stock manifolds, remove the divertor valve on the air tube manifold and adapt a 0-15 psi gauge and route the gauge into the interior. Run the on the road from 30 mph to 60 mph in high gear at WOT and watch exhaust pressure. It should not be over 3 PSI. If you have headers, adapt to the collector(s) or exhaust pipe to the muffler(s). Does tailpipe emission feel hot to the hand?

Assuming, cooling system is in good condition...all of the prevuios post, plus fan.shruods is in the right position...And no blown head gasket..
Do u have polished sump and valve covers...if so do they have cooling fins, are these polished or painted?

I just finished with the temp gun...

Got the car to running temp.

Dash Temp Gauge = 225/tip of redline
Thermo housing = never above 180
Radiator top hose side = 185 all the way across
Radiator bottom hose side = 160 toward the bottom, cooler toward the top/cap.
Shot the temp sending unit (in the head) and that read = 200

I don't believe the water pump is the long style. I also checked the fan/shroud by putting up a piece of paper in front of the radiator. It sucks it up when I hold one in front of it. I also took the 772 fan and clutch from my 69 Z and threw them on just to check. No difference. The pulley is correct for an LS6 (3995647AP).

It appears your sending unit may be at fault:
1. Wrong one for car/gauge
2. Sending unit not threaded in far enough -- it is measuring more of block temperature rather than coolant temperature, it is not in the coolant flow. Once again, the unit may be too short on the sensor side.

If sender is in the head, it may read hotter than sender being located in the intake manifold.

Are you sure about the bubbles in the coolant? Good sign of a head gasket gone bad.

The air being pulled across the radiator will be noticeabily hot to the skin/face if the coolant is 225*F. If the coolant is 225*F, you can bet the fan clutch will be kicked into action, air will be pulled.

Hmmm... I took that sending unit and boiled it with the gauge and it read fine... Perhaps I have a few more turns to go into the head. I will check that.. Does my system need a burp perhaps?

I'm gonna do the bubble check again. And when I get a chance have the coolant tested.

I agree with Everett, your guage is lying to you.

Do you or a freind have a surplus old fashioned capilary tube mechanical guage you could screw in for a test?

I need to look into that Jim.

or there's always the old standby. take the rad cap off, and run the car with your wife's meat thermoteter in the radiator, see how the readings compare. you'll be on the cold side so expect 20 or so degrees lower than the car's guage.

Don't let it get too hot, if it's as hot as your guage says, it'll boil without pressure.

I'll do it! But I might have to do it on the sneak. My wife the chef, certified in food sanitation would probably kill me. :)

I'll do it! But I might have to do it on the sneak. My wife the chef, certified in food sanitation would probably kill me. :)
LMAO!

Just get it washed and back in the drawer before she knows it left. Do not put it in the dishwasher, she'll know she didn't use it, and ask questions you do not want to answer!

I'm gonna do the bubble check again. And when I get a chance have the coolant tested.
Most auto shops have a unit that plugs into the radiator cap hole.
This then sucks the gases thru a fliud, which changes colour if hydrocarbons are present...quick simple. So much so it is not even worth the hassle of the book work charging to do.

Hey Darren, I have the headgasket/hydrocarbon tester your looking for. Give me a call and maybe we can get together on the weekend. Simple but effective test that may answer all your concearns.

Thanks for the tester Don. Everything tested ok. So not cracks or anything thank god. I did notice that as soon as I started the car that the level in the radiator sank to 1/2. Let the car cool and removed the hose from the thermostat and found that the coolant wasn't anywhere near the housing. Filled it up a bunch and put the hose back. Will give a test drive tonight... Thanks again Don for all the advice. Hopefully this will be the end of it.