LT1 Cooling, is this backwards? DOH!

[gvincent]

I attached a rather crude sketch of my cooling system and I think I have it backwards after reading this:

LT1 Coolant Flow:

 

The LT1 is completely different since it uses reverse flow cooling. The incoming coolant first encounters the thermostat, which now acts both on the inlet and outlet sides of the system. Depending on the engine coolant temperature, cold coolant from the radiator is carefully metered into the engine. This allows a more controlled amount of cold coolant to enter, which immediately mixes with the bypass coolant already flowing. This virtually eliminates the thermal shock present in the old system.

 

After entering through one side of the 2-way thermostat (at the appropriate temperature), the cold coolant is routed directly to the cylinder heads first, where the combustion chambers, spark plugs and exhaust ports are cooled. Then the heated coolant returns to the engine block and circulates around the cylinder barrels. The hot coolant from the block re-enters the water pump, and hits the other side of the 2-way thermostat, where it is either re-circulated back through the engine or directed to the radiator, depending on temperature.

 

All of this means that the thermostat housing is the INLET (opposite of most engines), while the water pump is the OUTLET. The water pump (outlet) on the engine runs to the top left (inlet) of the radiator. The lower right (outlet) of the radiator runs to the thermostat housing (inlet) on the engine.

 

This also means that the "upper" hose on the radiator would be connected to the water pump (mid/lower part of the engine) and is the outlet of the engine, so it should be hot with the thermostat open. The lower hose on the radiator is connected to the thermostat housing (upper part of the engine) and is the inlet to the engine.

 

The main concept behind reverse flow cooling is to cool the heads first, which greatly reduces the tendency for detonation, and is the primary reason that the LT1 can run 10.5 to 1 compression and fairly significant ignition advance on modern lead-free gasoline. Reverse flow cooling is THE KEY to the Generation II LT1s increased power, durability, and reliability over the first generation smallblock engine.

 

There are three main circulation systems for the LT1, while most engines only have two systems. As with most cars there is circulation through the heater core and the radiator, but there is a third system on the LT1 which includes steam vents in the head, along with a pressurized reservoir.

 

Coolant to the heater core comes from the water pump. The lower hose on the water pump is the heater core inlet, and should have a flow restrictor mounted in the hose. This is to prevent over-stressing the core at high engine rpms. The heater core outlet hose returns to the water pump at the upper hose connection, and also has a T-connector to the pressurized reservoir to bleed off any air.

 

This means I probably overheated the engine which is probably the cause of my knocking noise, would this caused a spun bearing knock or should I look for something else.

I feel so dumb and depressed right now.

Greg

scan00394.pdf

[deja]

That's pretty much the way I have mine plumbed. Only difference is I have a "T" fitting from the Camaro in series with the upper heater hose that the head steam pipe is connected to.

 

 

 

For filling and bleeding follow the instructions on http://shbox.com/1/4th_gen_tech2.html#radflush Trust me this works, It took me two times to get all the air out. Be careful not to allow vented water to get to your optispark. Also be sure to plumb your overflow in correctly or the engine will suck air back into the radiator, don't ask how I know that, LOL. Mine sits at 180 and will run up to 197 when it sits at idle for a while, low speed fan kicks in and it drops back to 180.

 

 

I attached a rather crude sketch of my cooling system and I think I have it backwards after reading this:

LT1 Coolant Flow:

 

The LT1 is completely different since it uses reverse flow cooling. The incoming coolant first encounters the thermostat, which now acts both on the inlet and outlet sides of the system. Depending on the engine coolant temperature, cold coolant from the radiator is carefully metered into the engine. This allows a more controlled amount of cold coolant to enter, which immediately mixes with the bypass coolant already flowing. This virtually eliminates the thermal shock present in the old system.

 

After entering through one side of the 2-way thermostat (at the appropriate temperature), the cold coolant is routed directly to the cylinder heads first, where the combustion chambers, spark plugs and exhaust ports are cooled. Then the heated coolant returns to the engine block and circulates around the cylinder barrels. The hot coolant from the block re-enters the water pump, and hits the other side of the 2-way thermostat, where it is either re-circulated back through the engine or directed to the radiator, depending on temperature.

 

All of this means that the thermostat housing is the INLET (opposite of most engines), while the water pump is the OUTLET. The water pump (outlet) on the engine runs to the top left (inlet) of the radiator. The lower right (outlet) of the radiator runs to the thermostat housing (inlet) on the engine.

 

This also means that the "upper" hose on the radiator would be connected to the water pump (mid/lower part of the engine) and is the outlet of the engine, so it should be hot with the thermostat open. The lower hose on the radiator is connected to the thermostat housing (upper part of the engine) and is the inlet to the engine.

 

The main concept behind reverse flow cooling is to cool the heads first, which greatly reduces the tendency for detonation, and is the primary reason that the LT1 can run 10.5 to 1 compression and fairly significant ignition advance on modern lead-free gasoline. Reverse flow cooling is THE KEY to the Generation II LT1s increased power, durability, and reliability over the first generation smallblock engine.

 

There are three main circulation systems for the LT1, while most engines only have two systems. As with most cars there is circulation through the heater core and the radiator, but there is a third system on the LT1 which includes steam vents in the head, along with a pressurized reservoir.

 

Coolant to the heater core comes from the water pump. The lower hose on the water pump is the heater core inlet, and should have a flow restrictor mounted in the hose. This is to prevent over-stressing the core at high engine rpms. The heater core outlet hose returns to the water pump at the upper hose connection, and also has a T-connector to the pressurized reservoir to bleed off any air.

 

This means I probably overheated the engine which is probably the cause of my knocking noise, would this caused a spun bearing knock or should I look for something else.

I feel so dumb and depressed right now.

Greg

[gvincent]

Thanks Deja,

So I do have it plumbed right, the only difference is that my head steam pipe is connected at the JTR "T" fitting on the thermostat inlet hose coming from the bottom of the radiator.

So my plumbing diagram is right, I just have the flow arrows in the wrong direction?

On the overflow tank I used the stock 280Z tank and just connected it to the radiator cap vent tube. I am using a pressurized cap, I don't remember the rating though. I also swapped out the 180 degree thermostat for the 160 degree one. (could I have put this in the wrong direction?)

I did have coolant squirt out of the vent hole on the top of the cap on the overflow tank though.

I haven't driven the car yet and have only run it on jack stands and now I have a motor knock. I was thinking I over heated it by not running the coolant plumbing right, now I don't know how I developed a knock, I certainly never over revved it???

I am racking my brain trying to think where I went wrong and what the rap is.

Frustrated!

Thanks,

Greg

[deja]

You really need to run the car for a long time to burp the cooling, like 20 minutes or more. Fisrt time I drove mine it overheated big time. Temp gauge was off the chart and the high speed fan was sceaming. Like I said it took me two times using shobox's method to get it burped. But I think the second time was because I had the overflow plumbed backwards, DOH!

I'm running a 160 thermo too. One thing you want to do in your PCM is lower the fan temps to 179 and 197. This is usually where the fan temps get programmed to when you add a 160 thermostat.

Do you have the knock sensor wired in?

 

 

Thanks Deja,

So I do have it plumbed right, the only difference is that my head steam pipe is connected at the JTR "T" fitting on the thermostat inlet hose coming from the bottom of the radiator.

So my plumbing diagram is right, I just have the flow arrows in the wrong direction?

On the overflow tank I used the stock 280Z tank and just connected it to the radiator cap vent tube. I am using a pressurized cap, I don't remember the rating though. I also swapped out the 180 degree thermostat for the 160 degree one. (could I have put this in the wrong direction?)

I did have coolant squirt out of the vent hole on the top of the cap on the overflow tank though.

I haven't driven the car yet and have only run it on jack stands and now I have a motor knock. I was thinking I over heated it by not running the coolant plumbing right, now I don't know how I developed a knock, I certainly never over revved it???

I am racking my brain trying to think where I went wrong and what the rap is.

Frustrated!

Thanks,

Greg

[gvincent]

Yeah I have the knock sensor wired in, I drilled and tapped the JTR setback plate and mounted it there. I don't have a working temp gauge, I need to trace the positive feed to the 280Z gauges as I don't think any of them are getting voltage except the volt meter.

I mounted a mechanical oil pressure gauge in the engine compartment and a mechanical water temp gauge. I will hook up the water temp gauge on the opposite side of the block that I have the Datsun temp sender on. In the hole that used to house the knock sensor.

I was going to remove my expanded plug in the water pump and thread it but that requires removing the water pump again, another time.

I believe I already lowered the fan temp but my fan is a single speed one from the Lincoln/Thunderbird, I thought it was a 2 speed because it had 3 wires but it isn't. So would I set them both the same for a 1 speed fan?

I will check my TunerCAT settings and see what I set the fan temps at although I haven't gotten past getting the SES light to go off so the fan comes on and stays on right now.

I think the motor knock/rap has got me flustered right now,

I need to go back to solving one problem at a time starting with a working temp gauge and a good running cooling system with no air trapped, then work on getting rid of the SES light and the Datsun gauges working.

If I spun a bearing or something then I will rebuild it later and swap in the Caddie LT1 that I have.

[MikeJTR]

Hi,

The steam vent tee should go on the upper radiator hose.

 

The three-wire fan is a two-speed fan -- it is possible that the fan motor is bad, and it only works on one speed. You should check the amp draw of the fan to make sure it does not draw more than 15 amps on low-speed, and not more than 30 amps on high-speed. Do not try to run high and low speed at the same time because it will draw a lot of current, and it won't draw more air.

[wheelman]

GVincent,

It's pretty much impossible to get an LT1 thermostat in backwards. If you installed a thermostat for a Gen I SBC it might be backwards but thats the least of the problems you'll have, the stats are totally different and a Gen I version will cause big time cooling problems in an LT1.

 

I agree with MikeJTR about the fan, if it has 3 wires it's definitely a 2-speed fan. I inadvertently wired mine wrong and managed to burn up three 40 amp relays before I figured it out. It's possible to use it as a single speed fan by wiring the "working" circuit to the high temp control from the PCM and then set the trigger temp low enough to kick it on when you want. I finally wired mine that way and it works fine.

 

Wheelman

[gvincent]

Thanks Mike,

I will take some pics of my plumbing tonight.

So I should of installed the JTR Tee fitting for the steam hose on the hose between the drivers side top radiator inlet and the lower drivers side water pump outlet?

The thermostat housing inlet with vent, passenger side, on the top of the water pump should be routed straight to the outlet on the bottom of the radiator?

I tried every single combination of the 3 fan wires and could not tell the difference in fan speeds they both were hi speed to me. I will have to go back and look to see if I wired it as a two speed or a one speed fan.

I will check it with an amp meter this weekend.

 

Wheelman, I now remember that I special ordered that 160 thermostat from AutoZone specifically for the LT1 motor. And as I now recall the 180 I took out looked almost identical to the 160.

 

Deja, So my plumbing diagram has the flow arrows backwards right??

I could not find anything to tell me which tube on the 280Z firewall was the heater core inlet and which was the outlet, Top or Bottom? I also read somewhere in another thread that the 280Z heater core or under the dash somewhere is a flow restrictor already. I have the LT1 heater hose with the inline restrictor module and the arrow heading to and connecting to the bottom firewall heater core tube and coming from the bottom water pump connection.

I have the top heater core tube connected to the top water pump heater connection using the LT1 vented hose.

I'll post the pics, easier to look at picture than describe it.

Thanks,

Greg

[MikeJTR]

The LT1 uses a "reverse flow cooling system." This means the coolant through the engine flows in the reverse of the old style small-block. It does not mean the coolant flows through the radiator in reverse.

The lower radiator hose (passenger's side) connects to the lower hose fitting on the water pump (thermostat housing).

The upper radiator hose (driver's side) connects to the upper hose fitting on the waterpump. The steam tube/tee goes into the upper radiator hose.

As for the T-Bird fan, the low-speed should be more than adequate for cooling the engine. Again, I have seen quite a few defective T-Bird and Taurus fans that draw excessive current.

[Bartman]

...So my plumbing diagram has the flow arrows backwards right?? ...

Yes, your flow arrows are backwards and like Mike pointed out the tee should be in the upper hose. In additon, you show a bleeder in the steam tube - which I don't think will work well. You should move the bleeder to your heater hose.

 

I initally had my tee in the lower hose and then switched to a setup like Deja is running with the steam tube going to the heater hose. Here's a thread discussing the tee placement and diagrams as well.

 

http://forums.hybridz.org/showthread.php?t=120477

[deja]

First I'll say Mike has certainly more experience at this than I do so I won't disagree with him. I had my car plumbed with his T in the radiator hose when I first finished the plumbing. There was a thread here about a year ago about this very thing. At that time I looked over my GM shop manual and decided to plumb it more like the Z28 does. Does it make any difference? I doubt it. But the way I have it works for me so I'm leaving it like that.

I totally agree with both Mike and Wheelman about the thermostat and the fan. You have a 2 speed and DO NOT run both windings at the same time, it wont help, will draw a ton of current and most likely will burn up the fan and or relays eventually.

I am not running a Datsun heater so I can't say which hose is which at the firewall. I am not running the restrictor with my Vintage Air heater. If your heater has one don't add a second one. But you have the hose coming out of the engine correct according to my GM shop manual. I am also running the complete Z28 wiring harness including the under hood relays where the fan relays are located. I'm still using them to power the Taurus fan but I had to add 2 more relays to prevent running both speeds at the same time. 1st relay powers the low speed winding through its NC contacts. When the high speed is needed the 1st relay and 2nd relay coils are triggered by the high speed Z28 relay which disconnects the low speed winding and sends 12v to the high speed winding through the 2nd relay's NO contact. BTW I have not had the high speed fan kick in since I got all the air out of the system. So you should be able to get away just running the low speed. But if the high speed winding burned up I wouldn't put much faith in the fan lasting too long.

 

Deja, So my plumbing diagram has the flow arrows backwards right??

I could not find anything to tell me which tube on the 280Z firewall was the heater core inlet and which was the outlet, Top or Bottom? I also read somewhere in another thread that the 280Z heater core or under the dash somewhere is a flow restrictor already. I have the LT1 heater hose with the inline restrictor module and the arrow heading to and connecting to the bottom firewall heater core tube and coming from the bottom water pump connection.

I have the top heater core tube connected to the top water pump heater connection using the LT1 vented hose.

I'll post the pics, easier to look at picture than describe it.

Thanks,

Greg

[a6t8vw]

. The steam tube/tee goes into the upper radiator hose.

 

that sentence is key..

 

cyl head steam vent must tie into waterpump outlet

 

i must have hit 260 deg 40 times before i got that right...

 

what i ended up doing was to drill and tap 1/8 pipe on the waterpump outlet and used 1/8 to 3/8 barb 90* deg fitting, works like a charm, dont even need to burp the system..

 

Im running griffion 3" alum radiator with 16psi cap, 160 deg thermo. and standard overflow bottle... i going to put the 180 thermostat back in , almost too cold now

[gvincent]

Thanks, Mike, Wheelman, Deja, and a6t8vw.

Attached are pics of my setup.

From what you guys say:

1 I need to move the tee to the top radiator hose on the passenger side and connect my steam hose there.

I do have the bleeder on the heater hose so I am ok there.

I should remove the restrictor heater hose and replace with a standard hose as there is a restrictor in the 280Z heater system already.

I need to see how I hooked up the fan, I did use the firebird fusebox and relays but I think I only have one of the speeds hooked up, I did not use the other wire and taped it off for the time being as I saw no difference is speeds. I will sketch it up once I check what I did this weekend.

Thanks again guys

Greg

[wheelman]

GVincent,

Which plug wire loom and wire set are you running?

I bought a set of LT1 wires and have burned a couple because they are to long and rested on the headers. I'd like to route mine the same as you have yours.

 

Wheelman

[gvincent]

Hi Wheelman,

It is the LTI Universal length from Taylor, I bought the wire set with the 90 degree spark plug end attached and bare leads with a bunch of old style crimp boots. and then bought their LT1 Opti end boot kit which was a disappointment because it came with 4 straight and 4 90 degree boots? I couldn't figure that one out, I ended up using the 4 straight boots from the kit and re-used 4 of my old Opti straight rubber boots from the old plug set. I had more than enough metal crimp ends to do the job. I also wasted money on their aluminum bench vise crimper and wire stripper, the stripper worked ok but the crimp sucked, I ended up re-crimping them.

The Loom holders are made by Russell, they look nice but the little plastic holders don't hold as tight as I would like them to and I ended up loosing 2 of them.

I will see if I can get replacement holders, otherwise I will buy a set of those 4-3-2-1 individual plastic wire holders that have a screw hole in the middle to bolt them to the Russell aluminum loom holder. The ones that come with the Russell holders are a split type with a plastic spreader type center pin that simply pushes into the hole on the holder.

 

to Install the wires I numbered the wires and put them on the plugs and then routed them as neatly and as best I could back to the Opti, I them marked them where I thought they should be cut, by mating them up to the correct Opti plug hole then and adding an inch for insurance. I then pulled them back out and put the Opti end boots on and cut and crimped them. I then re-installed them exactly the way I routed them earlier.

The drivers side is a piece of cake, the passenger side was a pain as I had to remove my custom plate which hold my 2 pulleys to route the wires behind it and up and around the LT1 accessory bracket to come out on top of the valve covers, I did re-use that little plastic clip on the accessory bracket that holds the 4 wires tight around the corner of the accessory Bracket. This was a plus, as it made it nice and neat, If I had bigger diameter wire though it would not of worked.

I did not gut the power steering pump but made a plate to house both a grooved and a smooth idler pulley that I scrounged at a junkyard to take the place of the AC compressor and Power steering pump. I still had to try several belts to find the right length and chewed it up a little until I got all the pulleys lined perfectly.

Although I haven't replaced the belt yet since I have other problems that are more important right now.

I still have the Taylor box at home and will post back the part number for the plug wire set.

Greg

 

GVincent,

Which plug wire loom and wire set are you running?

I bought a set of LT1 wires and have burned a couple because they are to long and rested on the headers. I'd like to route mine the same as you have yours.

 

Wheelman