86 Z28 312 A4

Here's my question....can radiant heat from the headers cause a heat soak condition on the temp sending unit, making the car to appear on the gauge to be overheating, but in actuallity it's running at the correct temp?

If that's the case, would using something like a DEI spark plug wire protector/sheath/boot be a good fix?

I've temped it at the radiator, right by the upper inlet in the fins, and it temped to 170-175*.

The sending unit, located on the head between cylinders 1 and 3 and the primaries for those cylinders, temped out to 225-230*.

Primaries temped out to 500-550*.

Gauge showed about 210-220*.

I've tried 3 gauges and 3 sending units- one was brand new. Same results with all combos.

THANKS in advance!

On cold nights, it reads cooler, on warm days, it reads hotter.

 

No, the headers won't really affect it.

However, it's actually measuring the temp of the head casting, not the coolant; it makes sense that it would show a higher temp than coolant temp, since heat is flowing FROM the casting TO the coolant. 2nd law of thermodynamics, you know: heat flows from a place of higher temp to a place of lower temp.

All of your temp readings sound pretty normal.

 

So basically I should just move the sending unit?

Any suggestions on where to?

THANKS!!!

 

Why?

What would you like it to measure? Whatever that is, put it there.

These 2 statements are inconsistent with each other. 210-220° is NOT "overheating" at all, not even close. On the contrary, it's PERFECTLY normal. In fact, the factory fan switch, doesn't even turn the fan on, until the temp reaches about 235°. IOW, in the factory's opinion (not that they would know anything about cars), the car NEEDS NO COOLING AT ALL until it reaches that temp. Coolant in a properly operating cooling system doesn't boil until around 265°. With that in mind, what's wrong with 210°?

I'm just not seeing where there's a problem. All of your temps are exactly what they're supposed to be in each place, coolant is flowing, heat is moving, the earth is even rotating! Life is good.

 

To measure the true temp of the coolant.

See above

I thought that's what the current location was supposed to do.

when you take 2 statements from different parts of the post, yes they are.

210-220* was read on a 45* night, while moving. At idle, it would creep up. On a 70* day, it was reading about 225-235 at 80 mph, and would creep up when I'd get into town, which to me says running hotter than a car should with an alumium high flow water pump and a 2 core aluminum radiator with a 170* stat.

My Blazer, with an OEM temp stat, never reads above 175*. Just as my 83 did. And the 84 I had. And even a *cough* nissan I had a long time ago.

I'm tired of the gauge needle reaching for the stars and worrying me while I'm doing 80 mph down the road, only to find out that the coolant temp is fine.

I'm also worried that, in the event that I do have an overheating problem someday, I'll have no way of knowing until it's too late.

 

Well if you just want the gauge to read lower, move the sending unit to the water outlet or intake manifold.

No its current location DOES NOT measure the temp of the coolant; it measures the temp of the head casting.

 

That just seems odd that it would measure the casting temp, and the only reason that the hole protrudes into the water jacket of the head is to cool the sending unit (?).

I guess I've always assumed that the temp gauge on ANY vehicle was there to tell you the coolant temp, not the casting temp of where it was located.

What would cause the casting to run so much hotter than before? My 83 with a 350 and 305 heads ran lower- even after a mild build.

Before on this engine (stock L69 before), it ran lower. Since a rebuild to .040 over, flat tops, Edelbrock 650 AVS, Holley Street Dominator intake, 416 heads are ported, polished, shaved .004, have 1.94/1.5 manley race flow valves and guides, cam specs are 214/224 @.050 lift is .442/.465, 1.6 Aluminum roller rockers, and the headers. It's still a 305 in the end, but even if I'm pushing a whopping 300 hp at the crank, it seems like it shouldn't run as hot at the head.

I understand more power equals more heat, but that much more?

Thanks again for all the help and info- I really appreciate it! I've got too much damn time primarily, and I'm sure money for being 'low buck', into this car to run into a problem down the road.

Also, at what temp should I worry about the casting if I don't move it?