appelen

Hi, I have a 90 ZR1 with a strange problem, when driving in 6 th gear below 1800rpm the temp gauge is creeping up to about 230 degrees and when i downshift to 5th with rpm little above 2k the tempgauge comes back down right away where it should be, anybody else ever had this issue? The car has a Dewitt radiator recently installed new hoses and waterpump, it did the same before these parts where replaced. Thanks

Tom400CFI

When the temp is creeping up, do you have heat from the heater? If no, you're not full on coolant. The symptoms are like that of a system that's low on coolant (has an air pocket).

appelen

Thanks for the quick reply, there is no heat coming out, what is the best way to get the air out of the system?
Thanks

ccmano

Here is Mr. Haibecks write up on filling the cooling system. I’ve always had good luck jacking the passenger side. Just go slowly.
http://www.zr1specialist.com/HAT%20W...ersion%203.pdf

However a better question for you is why is the system low on coolant in the first place? (Assuming that’s really the issue) Is there a leak or is there a head gasket issue?

At the risk of stating the obvious, was the thermostat replaced?

H

ccmano

Just giving this some thought.... should you find that the cooling system is actually full what you may be experiencing is something that is actually normal on an LT5. It has been documented that the LT5 water pump is marginal in its ability to flow coolant under 2000 engine rpms. Do some reading in “Dynomites” Solutions sticky. Volumes have been written on the forums about the cooling system and it’s marginal nature particularly in very hot conditions. Many have experienced exactly what you are seeing. Like you some have even installed more efficient radiators and fans only to see the same issue continue. Your probably not getting as hot as you think if your looking at the cluster gages. They are notoriously inaccurate. Track your actual coolant temps on the HVAC display. It’s written up in Solutions stick how to see your temp on the HVAC display.
H

Attached below is just one thread that discusses what your seeing.
http://www.zr1.net/forum/showthread.php?t=8812&page=2

HVAC display of coolant temps. Post #9
https://www.corvetteforum.com/forums...post1580070560

DRM500RUBYZR-1

What he said!
1800 is too low.
Downshift to 5th.
Marty

Dynomite

See post #7 in Sticky above regarding water pump flow rate and engine RPM.
Keep RPMs above 2,000 rpm for adequate coolant flow.


Water Pump Flow Rates
15 gpm at 800 rpm
18 gpm at 1,000 rpm,
44 gpm at 2,000 rpm,
65 gpm at 3,000 rpm,
90 gpm at 4.000 rpm,
120 gpm at 5,000 rpm at which time cavitation is starting.

Tom400CFI

I can't believe this car was check off by engineering...and it can't cool itself in high gear. How did GM get it through EPA fuel economy certs w/o overheating it??

OP heater should work in any gear at any rpm...even idle. So if you've got no heat, your low on coolant. Fill the cooling system.

appelen

Thanks everybody for your input, there is definitely air in the system after reading your replies, so I will look into that today, Thanks

Dynomite

If injector housing coolant manifolds are getting hot, the coolant is circulating and all air will be washed out in a couple cycles. Air will find itself top side of radiator and forced to coolant reservoir in front of passenger windshield and on to Coolant Overflow under passenger headlight. Keep that plastic coolant overflow 2/3 full as that replenishes engine coolant.

Make sure your Radiator/Coolant Reservoir Cap is functional!!!
If the Radiator (Coolant Reservoir) Cap does not hold 15 psi the Coolant Excess air will not be evacuated during a coolant temperature cycle.

glass slipper

I use 6th gear extensively including putting around at 25 MPH and have never had an overheating problem in over 26 years, not even close.

cv67

^^^ stop lugging your car your thrust bearing will thank you

Tom400CFI

The Thrust bearing? Which one...the one on the crank? What does it care?


We had a lengthy conversation about "LUGGING" a while ago. Posted vids and everything. Good read.

Dynomite

Seems to me Lugging means low oil flow, low oil pressure, and high piston, piston ring, piston rod loads (including wrist pin and crank journals)

Tom400CFI

Possibly. Let's examine each:

*low oil flow, low oil pressure: I put these two together since they're related. As I said in the other thread, (linked above), "As long as there is sufficient oil pressure, the engine won't "care" what RPM it's turning. the "problem" of "lugging" in this day and age, is not a mechanical problem....it's a psychological one." Since we have an oil pressure gauge, we can monitor the oil pressure. IDK what the minimums are for an LT5, but a Gen I/II is 10PSI for every 1000 RPM. My '92 LT1 generates 30 PSI at 700 RPM...so I have way more oil pressure than enough. I'd bet the LT5 is similar. Anyway, pressure is resistance to flow, so if we have good pressure, then we've gotten more than enough oil to the bearings, etc, to fill the spaces, create resistance to flow and build pressure. Remember, oil pressure isn't what is protecting bearings; hydrodynamic lubrication is. If the oil is there, it's protecting. If we have oil pressure, I think the "oil is there".

*high piston, piston ring, piston rod loads: I would submit two things here:
1. Combustion loads are higher (the highest, actually) at the engine's tq peak than they are at 1000 RPM, or at "low" RPM.
2. Reciprocating loads increase by the sq of the RPM and are obviously highest at the fuel cut off.

SO, the highest loads on the crank/pin/piston/rings would likely be seen at somewhere between tq peak and redline; where ever the combination of reciprocating loads and combustion pressure decreasing, crosses paths.

In the olden days, we had very poor, or no control over fuel ratios, timing and even combustion quality. The LT5 has an advanced combustion chamber and some of the most advanced timing and fuel control of it's era. Therfore combustion is well controlled, smooth pressure rise, no detonation etc. Shouldn't hurt the engine one wit, if you've got enough oil pressure.

Finally, although you CAN go WOT at 500 RPM...no one said anything about doing that. So if we're rolling through our neighborhood in a high gear at a low RPM, and the throttle is bearly cracked...what is our manifold pressure? What is our combustion pressure? So, how are we having "high piston, piston ring, piston rod loads (including wrist pin and crank journals)"


.

appelen

I have planned to install a 3.73 rear end ratio in the next couple of months , maybe someone that. Runs a 3.73 rear end could chime in, what kind of rpms are you showing at 70 mph with standard diameter rear tires? it should kick up the rpm some which would help the cooling at highway speed in 6th gear.
Thanks

Dynomite

If throttle barely cracked you are NOT lugging anything. The term "lugging" was used which to me means you gave it some gas in 6th gear/slow speed