Correct engine coolant temperature

[salvatore1]

Originally Posted by scottfab

If the High presure side of the AC line never reaches 240psi then the
fan does not get told to turn on. Check to see if the AC is working.
Does it get cold? If so maybe the fan or (of fan relay) is bad?
Check connection at the fan.

my A/C definitely comes on cold. I did notice the drivers side fan was hard to turn with my hand, then it felt like it broke loose and I could turn it again. I see two relay looking things together on the left side of the fan shroud - are these the two relays?

[QB93Z]

Originally Posted by PhillipsLT5

Change to 4.10 gear

You are correct about 4.10 rear end. The '93 has a 4.10. Same effects that I noted. It just happens at different speed/gear combination.

As far as using a pressure cleaner hose to blow crap out of the radiator, be very careful. The fins in these radiators are very thin aluminum and it would be easy to bend them over with a pressure washer.

Thanks for the warning about reducing the bypass flow and causing over pressure in the radiator. I plan to proceed carefully. The over pressure problem will only occur at high water pump flow (engine rpm at 7000). At that water pump pressure, the coolant bypass will be opened against its spring pressure.




What I am trying to reduce is the bypass flow that occurs all the time (even at low pump pressure) because of the notches in the bypass valve disc.

I would like to find a ZR-1 that doesn't do what I described and find out what brand thermostat it has.

Jim

[QB93Z]

Originally Posted by tomtom72

I agree, I think. It appears to me that my 90 will become more heated if I spend much time in the lower gears, like doing road work where 3rd & 2nd & 4th are used alot....specially if I slow down and cease playing and drive normally. At that point it appears that I heat soak for a good while till the cooling system calms down or catches up to the heat load that I just generated by my sophomoric behavior......it appears that the higher I go in the rev band, and the longer I stay higher in the revs, the more by-passing takes place in my 90's cooling system? It appears if I insist in living up past the 4k mark that after a good while the oil & coolant temps start to spike even if my velocity is at a good clip. I seem to get my best cooling performance when I can keep to about 2k or below in 5th or 6th with a constant speed. Maybe I have something malfunctioning?

Tom,

I think you are seeing two effects.

1. If after a period of spirited driving (increased engine heat load), the temperature is high, you may have a radiator fouling problem. But if the temps are not way high, then the fouling problem is not too severe.

2. The worst cooling capability for my LT5 occurs at light load (5-10% throttle) and low rpm (< 2000 rpm). Because of the notches in the bypass flow valve there is barely sufficient water flowing through the radiator to remove the heat load. At these conditions, even with a perfectly clean radiator and perfect air flow (both fans running) the temperature of the coolant will rise way above the desired temperature.

Jim

[tomtom72]

Sal, yes the two relays that you find on the left side of the radiator shroud are the fan relays. It sounds like one of the motors has a bearing issue if it wouldn't turn freely. I'd keep an eye on that one.


Jim, thanks for your advice. I will have to admit that when I was trying to clean my OE radiator that after a while I gave up on the sand particles....I didn't get them all for sure!

Oh well, I guess it's time to start shopping for a new radiator as I'm very OCD about the coolant dump & flush & t-stat R&R every two yrs. Perhaps a Marc Haibeck EPROM is in order also.

[QB93Z]

Tom,

I definitely recommend the Haibeck chip for the fan control feature as well as all the other improvements it offers.

I wonder if there is a way to use a local radiator shop to dip clean the stock Corvette radiator. I don't know if that can be done to the plastic tank radiators though.

Jim

[secondchance]

Jim,

I replicated and confirmed that my Z with OEM thermostat does the same thing.
Sustained 55-60 mph in 6th - 213
Down shift to 5th, temp drops to 202
Sustained 65 in 6th - 208

Ambient temp was around 84.

Generally I prefer not lug the motor so I don't get into 6th unless I am running sustained 70 plus. That's probably I was never aware of this.

[QB93Z]

SC

Thanks for taking the time to check this out.

I am trying to figure out if the notches in the bypass valve have some other purpose in the overall cooling system operation.

Possible reasons for the notches might be: faster engine warm up when starting in cold weather; better responsiveness by the thermostat; improved heater operation with cold engine; temperature stabilization of the entire cooling system; or I don't know what else.

Ideas anyone?

Jim

[Aurora40]

Originally Posted by QB93Z

In both cars when cruising at about 55 mph in sixth gear (about 1600 to 1800 rpm, the coolant temperature will rise to around 225. If I shift to fifth gear, (>2000 rpm) the temperature immediately drops to around 203-205.

Jim, I don't believe this is coolant bypassing the radiator. That should only happen when the pressure gets high.

I posted about this on the listserv a while back. I believe it is related to the flow capacity of the pump at low rpms. Graham Behan sent me a chart of the flow rating at various rpms, and mentioned it was likely that at those lower rpms, the pump does not flow enough. This is why downshifting helps.

[QB93Z]

Originally Posted by Aurora40

Jim, I don't believe this is coolant bypassing the radiator. That should only happen when the pressure gets high.

Bob, Looking at the picture I posted, the bypass valve has two openings (notches) that allow flow to bypass the radiator even when the bypass valve is closed (low pump pressure). In the picture only one notch is shown. The other is just as large and together I think that they cause a relatively large amount of water to bypass the radiator even at low water pump pressure/flow.

Jim

[Aurora40]

I hear what you are saying Jim. I was thinking further about this. I suspect if the pump pumped so little that it all bypassed the radiator, then the car would not cool down when idling. Yet that's not true, at the lowest flow point, the car can still shed heat when the fans turn on at idle.

FYI, while hardly definitive, I had a quick write-up in HotB issue 15 if you want to give it a quick read.