Big Block C3 bizarre temperature measurements.

[Bad Bird]

Hi all,

I've had my big block Corvette less than a year, and it's been extremely reliable. I've never trusted the temperature gauge however, as it's almost always hovering around the first quarter mark. To cut a long story short, I went on a long cruise in ~90 degree weather (maybe 30 minutes at 60-70 mph, then an hour in stop-start traffic) and for the first time ever I saw the temperature gauge go up to about the 180°F mark on the gauge. This gave me cause for concern, as I had always just assumed that my gauge was off and that the first quarter mark was 180°F.

I had a non-contact IR thermometer in the shed, so I spent this morning attempting to re-create the 'overheat' condition. To start with, I went around the block to get some initial heat and see what the thermometer said. At this point, when I measured the heat on the upper rubber radiator hose I got something like 150°F, and the lower hose was very cold.

I then took the car out onto the open road for an hour (day off, and it's fun to just drive the 'Vette sometimes). To get the situation, I pulled the TH400 back into 2nd and drove along for a while and eventually got the temperature on the gauge to go to what it was during the 'overheat'. What I found when I measured the temperature at the radiator hoses was that the bottom hose seemed hotter than the top! (~188°F top, 197°F bottom). The car was idling at the time, btw. I got a maximum of 212°F at the top of the painted thermostat cover. It seems like the car really isn't overheating, but what would cause the lower rubber hose to be hotter than the top?!

 

[clutchdust]

First off, I would not measure on rubber hose with an IR thermometer. I have never been able to get an accurate reading that way. Rubber is, after all, an insulator. So to start, I think you're baseline measurements are skewed. With the IR thermometer, you're best off taking readings on surfaces as close in construction and coating as possible, i.e., painted vs nonpainted surfaces and iron vs brass or aluminum can all vary slightly in readings. Thick cast iron vs thin sheet aluminum or brass adds yet another element. Combine multiple factors and you can be chasing a problem that really isn't there.
My suggestion is to get a set of ramps, drive the car to simulate the condition and then park the car on the ramps with it running. Then take a reading on the radiator tank where the hot water dumps into the tank and follow that by a reading on the lower outlet. It will most likely require you to crawl on your back to get the reading, hence the ramps. But I feel that you need to start with good raw data before troubleshooting.
As for what you're seeing, the only number I see that's likely viable data is the number off the waterneck. While 212* is warm, I doubt that it's significant in a big block shark. They are notorious for cooling problems. If you are unsure, I would also suggest switching to either a 180 (my preference) or 160* T-stat. I think 160* may be a little too cool for a weekend cruiser.

 

[Bad Bird]

Thank you for the response. What I've done is borrowed a good thermocouple probe from work, so I can avoid the issue of different emissivity/IR output due to different materials. I'll try and get some results from the radiator itself.

Regards,
Matt.

 

[JeffP1167]

I personally wouldn't take any temp reading from anywhere but the rear of the cylinder head area since that will always be the hottest area due to slow circulation of coolant.

 

[clutchdust]

Hey Jeff, I won't disagree with the logic behind your statement but right now I think the OP needs to determine if his cooling system is functioning somewhat normally, and to do that he needs first to determine /\T across the radiator.
Once he knows he's cooling the water sufficiently, then I think we can hunt hot spots. But not being a big block expert, what options does a BBC owner have at reducing those hot spots? Maybe make a crossover tube for those blocked off rear water jacket ports? That's always been something that bugs me about the standard Chevy design. I've thought about drilling and tapping those block off plates and tying them together and then running them up to the front waterneck. Don't know if it would really do any good. But I can't see it doing any harm and would make me feel warm and fuzzy inside.

 

[mrvette]

Hey Jeff, I won't disagree with the logic behind your statement but right now I think the OP needs to determine if his cooling system is functioning somewhat normally, and to do that he needs first to determine /T across the radiator.
Once he knows he's cooling the water sufficiently, then I think we can hunt hot spots. But not being a big block expert, what options does a BBC owner have at reducing those hot spots? Maybe make a crossover tube for those blocked off rear water jacket ports? That's always been something that bugs me about the standard Chevy design. I've thought about drilling and tapping those block off plates and tying them together and then running them up to the front waterneck. Don't know if it would really do any good. But I can't see it doing any harm and would make me feel warm and fuzzy inside.

I had bought a L98 from a '87 vette coupe, just like what was in my '87 vert....was going to use it for a boat, wound up selling it off in pieces.....

sold my '87 and bought this '72....so had tons of parts including induction for this car.....one thing I noticed really quick was all that extra plumbing for getting the REAR crossover water into the suck side of the heater core return on the pump....so when installing it in my '72 I followed suit....

since then there have been many iterations of this engine and the latest is a highly modded LT-1 intake on the L98 basic engine....the crossover passages in rear are still plumbed forward to the water pump....

the heat shown on the engine is fairly even, I"d say IR and heat sink compound on the metal with probe...

I dunno jack about BBC, never owned one....

:surrender::smash:

 

[SmokinBBC]

I use an IR to check in and out. Even though the actual reading may be off, the lower is always at least 15 to 20 degrees lower than the upper.

I measure the rubber hose a couple of inches past the thermo housing and a couple of inches after the metal coupler on the lower hose. The further away from the engine block, the cooler the hose.

My upper hose has never exceeded 190 in the hot summer and is usually in the 185 range. When it is at 190 the guage is right on the first mark.