ZR1

OK, I thought we could have a little discussion here about the cooling system and the notorious bypass we have to save the stock radiator. The following picture is a rough drawing that has the basics of the whole thermostat housing.





In the above we can see the cooler water coming from the radiator. We can also see the bypass system. There is always a bit of water coming from the bypass due to the slots cut in each side of the stopper. So, you can see from the drawing that the basic operation of a thermostat is there. The heated water will cause the wax pill in the thermostat to expand overcoming the force of the spring thus opening the passage so the water from the radiator will flow. Pretty standard stuff.

What is unusual for us is the bypass stopper to the right. When the pressure from the bypass is great enough it will force the stopper to open allowing the water from the bypass tube (when looking the the cooling tube right below the intake you will see the left tube going to the radiator and the right tube going down to the thermostat housing) to enter the housing. With both the radiator side open and the engine side open water will take the path of least resistance and go to the engine inlet.

So, the real question here is a simple one. Is there enough pressure from the bypass that will effectively stop the flow of the water from the radiator outlet? The thermostat will not close so that path of flow is still there, however, is the pressure so lessened that there is no flow from the radiator?

If these questions cannot be answered, then how can they? Does anyone know how to make some sort of mounts for pressure sensors that we could measure the pressures and make an educated guess?

Come on folks, we got some smart people out there! All I got are questions!




[Modified by ZR1, 7:42 AM 3/18/2002]

Tyler Townsley

You and I have talked about this several times. you have the basics right and understand how it works As I understand it the stock system can flow up to 50-60 gpm (X inlet pressure) , the pump will put out 85-100 gpm at max rpm (Y inlet pressure) so to keep the system from blowing hoses/seals GM could put in a higher flow radiator or design a system to keep the inlet pressure below the X level, the latter being what they did. Note it is not the thermo causing the back pressure its the radiatior itself therefore its not that we are stopping flow at the outlet, the flow stopper is the pressure seen at the radiator inlet. In a new stock system the spring design starts flow around the radiator at 5200 rpm and by 5800 rpm all water is flowing through the bypass because the inlet pressure AT THE RADIATOR is acting like a stopper.

The following are my own thoughts.
As time goes by with a stock system the flow capability of the radiator becomes less so the inlet pressure increases at the bypass and your rpm induced flow around is brought on at even lower rpms.
Switching to a higher flow radiator should raise the flow around rpm but from what I have seen it does not eliminate it.
You must keep the bypass in place if you run a thermo because of the placement of the thermo after the radiator (ask me how I know it was painfull).
According to Lane Goldstein the system does not cool with no thermo in place.
You can cut the puck spring in the thermo and block the bypass if you have a high flow radiator, your hot interstate temps will be near 160/165 as long as its over about 70 deg. In town sees 195-210(90+ outside).
I run my fans all the time if the temp is over 80.
You can gain some additional cooling by increasing the fan voltage to 18 V DC (LPE uses this trick)
The most ofter overlooked cause of high temps is trash between the AC cond and the radiator.

Thats all I know.

Tyler

ZR1

OK, so your theory is that there is enough of a restriction in the old radiator that the increase in pressure will cause the stopper on the thermostat to be forced open. At least that is what I read in your post. So, even though the pressure at the radiator opening was high when it entered the radiator chamber the pressure dissapated throughout the cavity. Well, wouldn't it make sense that the pressure at the outlet of the radiator be high also?

Now this is one thing I never understood about your fix. You had previously indicated to me that you cut the spring located around the "pill". After looking at the whole thing, reading in the maintenance manual, etc., I just don't see how that would do anything other than keep the thermostat opening open all the time. I fail to see where it will help because that thermostat will be open even in bypass mode. Now, let me say this, what I don't know is if the spring around the "pill" along with the pressure from going into bypass mode is sufficient force to effectively shut the opening coming from the radiator outlet. If it is then I can see how your fix would work.

Tyler Townsley

My fist objective was to get my coolant temps down to less than 170 degrees on a 90 deg day outside. I bought a aftermarket high flow radiator thinking that I could score a 160 deg thermo and make that happen. Well I could never score a 160 thermo so I asked Lane how hw cooled his motor before going to the electric water pump. He said he tried the no thermo method and it would not cool so he cut the spring and it worked. So using his experience I did the same. This put my temps where I wanted them in the summer and a little cool in the winter. You can overcome this by using a piece of cardboard over the radiator when the temps get below 60 deg. I ran the car several years like this but noted that high rpm shots still spiked the temp so I tried the pluged bypass to see if it would work and it did. Lane never worried about that part as he cooled his down to 160 before each run and saw 185 or so at the end of the quarter. To get better control he has gone to an electric water pump setup.

How is the pressure at the outlet going to be high? Its got a waterpump that flows 85-95 gpm trying to suck the water from the hose at that point. The point is that the radiator chamber is not dissapating the pressure, the flow through the chamber is the limiting factor not the size of the inlet tube. Going to a high flow radiator may completely eliminate the bypass pressure point being reached but I could never prove it. My problem and yours too from what I can tell is how to get the water temps down where you like them. The first thhing would be to use a 160 deg thermo which is hard to find. I paid $100 for mine 2 years ago and thats what I run. The temps are a little higher than what I like but I do not do any prolonged high rpm stuff. To anyone who drives a ZR1 my first recommendation is to go to an aftermarket radiator and a 160 deg thermo. If you cannot get the 160 thermo then go the 185 unit. This is for normal usage! It you do any autox or road races then I recommend you do something about the bypass as it allows water to flow around the radiator at high rpms. Why do you think these guys that run the ORR have to go to 6th to cool the car? Its because they have hit the rpm that causes the bypass to function (Curtis you listening?) so to those I recommend pluging the bypass and the only way I know how to do this with the thermostat in its current location is to cut the pill spring and block the hose.
The bypass serves TWO functions the first being a path to allow warm water a path to get to the thermo and the second is to function as a pressure bypass to keep the stock radiator system from harm. If you have an aftermarket radiator system you could probably make a plug for the bypass with a 1/4-1/2 in hole and run a stock thermo but I never could find a standard design 160 deg thermo with the right diameter to try.

Again I cut the spring to get around the 190 deg pill not to get around the bypass, it was only later that I experimented to see if this would also allow pluging the bypass and it did.

Tyler
863-428-1410


[Modified by Tyler Townsley, 3:49 PM 3/18/2002]

ZR1

So basically you are allowing water to flow the the "normal" passages all the time. That is all I can see that can happen if you cut the spring around the pill.

OK, so how about this. Keep everything as it is. Carefully remove the spring that holds the stopper for the bypass. Next, weld the stopper where its at and replace the spring as a backup. Or, simply get a stronger spring and replace the stopper spring with a heavier one.

Of course, all this is dependent on you having replaced the original radiator with an all aluminum one.

ZR1Pete

So in plain English if i never auto cross or rr my Z and just drive it normal and just drag race it once in a while will any of this stuff help keep my Z cooler.
I have stock radiator, 180 stat with four 1/8" holes is it possible to make it run cooler then what i did,i would like to drop another 15-20f for around town driving when the outside temps are 85f +

Pete 91 #1635 PoloGreen/Saddle

W i l l

It seems as though the problem is the design of this flat plate bypass valve and spring system itself. When the critical rpm (water pressure) is reached to open the bypass, pretty much the entire flowstream is allowed to bypass. In other words, the bypass valve is not throttling the flowstream in the way you want it to. What you want is a bypass valve that will keep the inlet pressure to the radiator at the maximum pressure that the radiator can stand. What we have is a system that when the bypass opens, allows the radiator inlet pressure is to drop substantially. With a proper throttling valve bypass system, the stock radiator and cooling system would be much more effective at high rpms.

Since I watch Junkyard Wars a lot on TLC, here is the solution I would bodge together. I would put a pressure transducer on the radiator inlet. Also install a pintle type valve with stepper motor actuator in the bypass line. Use a simple PLC to open or close the valve so that the radiator inlet pressure is kept at a desired, preset value (lower for stock radiators and higher for high flow radiators). A system like this would always keep the radiator working at its full potential (NOT bypassing way more water than is needed).

A simpler and less effective solution is what others have done... just cut the bypass spring on a 160 degree thermo, install a high flow radiator, put a plug with a 1/4" hole drilled through it in the bypass hose and call it good.

Any other problems need to be solved today?

Tyler Townsley

I knew I could count on you to talk about farm tractors when we were speaking about cars, typical cowboy engiineering. This is a guy who takes on english farm tractors with an econobox, he lost, problem solved. LOL In your simple solution you do not need to cut the spring, just plug the bypass with a 1 in pvc pipe cap with a 1/4 in +/- hole in it. In a stock system there is a 600 rpm transition stage, 5200 to 5800 so its not quite as on/off as you said. What we need is a radiator that can handle 100+ gpm, cool the water to whatever thermo we put in it at whatever rpm we turn the motor, oblivious to the outside temp and car speed. Yeh that would be my wish, but it ain't going to happen so the above discussions give you insight on what comprimises can be made to fit your needs.

As I have said in the past, read the discussions as it helps you understand the dynamics of the ZR1 then decide what fits your driving envelope and apply the suggestions that you are comfortable with.

Tyler


[Modified by Tyler Townsley, 8:43 PM 3/18/2002]

Tyler Townsley

What water temp do you want to see and what is your load factor/outside temps? You want to run cool (160-185) all the way to 7400 in a high heat environment then you need a 160 thermo, fans on all the time, high capacity radiator, and minimal flow around the radiator(Bypass) and some way of venting underhood air at low speeds. You want to run even cooler or cannot find a 160 deg ZR1 thermo run a cut thermo with the other recommendations. You could try a stock 160 deg thermo and the bypass with a hole in it provided you can find/make one with the right diameter. You cannot drop 15-20 deg with a 190 deg thermo. It will always run at least that and tend to run 220-230 in traffic temps on a hot day. It has been pointed out by others that this is/was acceptable temps for this car which is true but 'I' am not comfortable with those temps. You have read what I did, make your own choices, I have said too much anyway.

Tyler

ZR1Pete

Thank You Tyler
I think that answers my question. If i understand you right.
I did cut and make a 160 thermostat out of another application stat that doesn't have a bypass spring plug,since i'll be getting a Griffin radiator i can use it and plug the bypass with only a 1/4" hole in the bypass plug.
Do i have this right.
Please advise so i don't make an expansive mistake with the new radiator.
Thanks
Pete 91 #1635 PoloGreen/Saddle

Rkreigh

very informative. I'm not sure why a hole in the bypass "plug" would be needed (bleeding??). another option is to just put a treaded rod through the think to hold the bypass flap open full all the time. the spring becomes ineffective. I have a Ron Davis going in, and am considering disabling the bypass as it's just stupid to not circulate coolant through the radiator at high rpms where the engine is producing LOTS of heat. GM should be drug behind one of their fancy ZR1s for :bs like this. putting a postage stamp plastic tank EXPLODING radiator behind an LT5 makes me ill.

I have one more radiator question. has anyone "laid down" the radiator to be nearly horizontal aka what mallet does??? I realize MAJOR mods would be needed but it would free up front room for turbos/intercoolers which is what I'm trying to do. by front mounting the turbos up high, I can gravity draing them. a "split duct" in the nose would route air to the intercooler and radiator separately. Custom plumbing and brackets will be needed along with a custom radiator. one thing for sure, the bypass WILL be plugged for this TT project!!!

very informative posts. this system is a confusing kludge to save a few bucks. I bet the R&D to develop it ended up costing more than just putting a decent radiator in it and calling a day. no logic there. :D

Tyler Townsley

I believe that can be done and was going to try it but found the correct stant 160 deg first. What you have to watch for is the water boiling at the motor before the thermo opens which is what happened to me. The motor acts like you have not purged all the air from the system, yet you get no air when you try to purge it. What is happening is the hot water is not getting to the thermo to open it before the motor gets hot enough to sent the temp guage over 230 deg. Very confusing since this is what happens if you do not get the system purged.

You may have to play with the hole size but I think 1/4 will work. You can start with a larger one and work down if you want to play safe. Does your 160 deg thermo have the same or larger hole open size as the stock? I looked at several before I found one that had a large enough inside dia to flow the same as the stock one.

Tyler

Tyler

Tyler Townsley

You do not want the bypass OPEN as that will let the water flow around the radiator! You plug that line to keep that from happening but you HAVE to let enough flow though to heat the pill to open the thermo side or you will cook the motor before it gets hot enough. The only way you can disable the bypass function completely (pulg the line) is to run a cut thermo that allows enough circulation through the system to open it the rest of the way or cut the spring out completely.

Tyler

ZR1

To cool things down perhaps a simple fix would be to drill some holes around the thermostat that the rubber gasket fits around. This wold always allow some water to flow through but still, you would eventually reach the 190 degree opening.

I am going to investigate replacing the spring on the stopper. As it has been noticed, you don't want to completely cut the water off in the bypass as it does serve to slow the flow through the radiator which allows the water to cool more.

Or, how about this, drill a hole in the stopper shaft and put a small cotter pin in there that only allows it to open so much. You are limiting the amount that can go through the bypass and still maintain a useful amount passing through the radiator.

91mongoose

The main reason I can see that you'd have to cut the thermostat puck spring when eliminating the bypass is that the bypass is what allows water to circulate pre-thermostat opening. On a normal small block the heater hoses route off of the water pump and the intake manifold. This allows water to flow through the engine during warm-up preventing hot spots and getting the warmed water to flow over the t-stat. On the lt5 the bypass performs this function. If you block the bypass the T-stat would never open because the hot water would never get to it, not to metion the water in the heads would heat far more quickly than the water in the rest of the engine.

Cutting the spring vs. removing the t-stat when blocking the bypass serves to slow down the water flow to aid in heat transfer in the radiator. The same effect could be achieved by replacing the t-stat with a restrictor disc.

The only way to keep the t-stat and remove the bypass would be to make a new setup for the existing t-stat housing that would be a straight through pipe with a fitting for the heater core return hose. Then you'd put a normal small block t-stat into a housing on a new cross-over pipe at the top of the engine. I would think the housing should go at about the spot where the radiator return pipe is now. You could then use a standard SBC t-stat neck as the bottom part of the housing, that's where you'd attach the radiator return hose. That housing would also have a fitting for the heater core supply hose. This would allow for warm-up flow of water through the engine and across the t-stat.

Does this make sense to anyone?

Tyler Townsley

Keep in mind we are playing with the bypass to reduce/eliminate water bypassing the radiator if possible, in a stock configuration this is not possible without a primary water path that allows some water flow through the thermo so it can open before the motor creates a runaway heat condition. Our cheapest/easiest option is to constrict the bypass route to the minimum flow needed to open a thermo. The easiest way is to use a hose clamp on the bypass hose going to the thermo to hold in place a 1 in pvc pipe plug with a hole drilled in it. Put it about 1 in from the bottom of the Y and make sure it is tight otherwise it ends up at the thermo housing, still works but harder to get at(ask me how I know that). Easy to remove/change until you get the hole the right size and you do not loose much coolant. The bypass serves two functions neither of which cools the engine. Taking the system apart at the thermo is a PIA and you get coolant/water everywhere. If you have the thermo you want in the motor and you have an aftermarket high flow radiator the easiest way to reduce flow through the bypass is using the PVC pipe plug.

Tyler

W i l l

Okay, so my complicated fix doesn't seem to have generated as much interest as the simple fix that everyone knows about. Well here is an alternative solution:

Mr. Lingenfelter's boys, along with other gentlemen, have managed to place intercoolers in the front of the twin turbo ZR-1s which are barely noticeable. A small radiator in the same location piped inline the bypass circuit will cure the problem. With this inexpensive additional radiator, hot water bypassing the stock radiator would come back to the engine nice and cool instead of getting dumped directly back into the engine. No other changes except the OEM style thermostat of your choice are needed. Please send all royalty checks to my rental car reimbursement fund.

Since this problem is now laid to rest, lets talk about the oil cooler that has a wax pellet thermostat with too high of a temp setting.

Tyler Townsley

One has to remember Will is a petrolum engineer so he had to get oil into the discussion somehow. We laid that one to rest years ago, now with all the new people you dun undid it again. I am staying out of the oil cooler discussion.

Tyler

PS You going to BG? Got our room yet?

ZR1

Shhhhhh.... Will... they don't know about that one....

xsmph

You can gain some additional cooling by increasing the fan voltage to 18 V DC (LPE uses this trick)
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Tyler, how do you do this? My problem is not high rpm but idling in traffic and getting 220-230 deg after 30 min. or so.