I know this problem has been argued about several times on this forum, most specifically in this thread: https://ls1tech.com/forums/advanced-...hermostat.html Also, I tried posting in the general LS1 folder, but have gotten no responses.

I'm working on getting an LS1 from a 2004 GTO installed in a 86 Porsche 951. Because I had to use a CSR T-stat housing for fitment reasons I'm not running a t-stat at the moment. After reading around on this forum it looks like I f*&$%#$ up big time, because most of my coolant is re-circulating in the block. Hence my overheating problems, and inability to purge the air from the system.

I don't have a lot of experience with cooling systems in cars but have taken several years of thermodynamics and fluid dynamics so I know the theory quite well.

My Questions:

1. I'm not 100% sure what the bypass passage I need to block up looks like. Does anyone have some better pictures, a more detailed description, or a link to a thread I missed? What methods of blocking have people used? I'd rather not have to remove the engine from the car.
2. Right now I have a small U-bend going from the heater core inlet to outlet, which if any of these ports should I block? I may eventually add a heater.
3. Of course any general suggestions for my overheating problem, it just sort of steadily climbs. It may start slowing down at around 215*, but at that point I get scared and shut it off anyway.

 

Hi,
i'm trying to understand your issue. A few questions????????
Are you parked at idle?
Do coolant fans turn on?
Timing/ a/f correct?
Do you have a fan blowing into radiator? High velocity!!
If you are bypassing heater core/make sure the hose is not bent restricting flow of coolant.
The thermostat controls open/close/ when coolant circulates......
As you know from your expertise..
Things to check:
Radiator cap/drive belt/water pump/engine oil(grade 5/30/temp gauge
blocked/dirty radiator.........i think that covers most everything...........
Have a blessed week....................captain jim

 

If you drove American,

I could recall how to help you out,

What'd the porsche guys tell yah

 

Thanks for the quick replies guys, I really appreciate it. Since you all seem willing to help out I guess I'd better start from the beginning! Any suggestions on the problem as a whole are definitely appreciated, but I'm really interested in more information regarding the bypass passage around the T-stat that I have to plug if I remove it. I don't know exactly where it is, or the best way to plug it up. I'm also not sure what to do with the heater ports. Like I said I just have a u-bend going from one to the other, which according to jim is fine (there are not pinches in the bend).


So anyway, I bought a 1986 Porsche 951 (944 turbo) a couple of summers ago after my freshman year of college. I fell in love with the handling and looks of the car immediately (I know many of you will disagree with the latter statement ) but didn't like the old four banger all that much. The previous owner had also put a ton of abuse on the engine and turbo leaving it in sad shape, knowing I wanted a fun driving car and good weight balance led me to the LS1 swap. I performed the majority of the swap last summer, here is a thread to my build (NOTE: I STOPPED UPDATING ABOUT HALF WAY THROUGH THE SUMMER LAST YEAR SO IT'S REALLY OUT OF DATE):
http://944hybrids.forumotion.com/t57...sche-ls1-build I did all the custom machining and fabrication and I had a great time. Things such as a LSD and wider wheels are on the shopping list, along with many other smaller things.

As it sits now the car runs and drives, with no problems except for this overheating issue. The engine is bone stock from a 2004 Pontiac GTO with 80,000 miles. The only things I did were an intake (detailed below) and exhaust. 1.5" primaries to 3" collectors, Y-pipe out to 3.5" and then a 40 series flowmaster. No cats or anything. Didn't go with duels because of space restraints, but it sounds great anyway.

To answer some of the posed questions:

-I am using an after market VDO temp gauge and sensor. The sensor is screwed into an Autometer adapter in the drivers side head. The temperature reading climbs steadily from startup without any weird jumps or anything, near the end of the run the temp seems to climbing more slowly but it's hard to tell.

-It will overheat either at idle or when driving, although if I put my foot into it at all the temp reading obviously starts to rise more quickly, but not alarmingly fast.

-Right now the fans are always running at full speed, I'm using the stock duel fan setup from the 944 which was meant to handle the heat from cooling a turbo. The radiator is a Griffen 1-26201-X. Many guys that do this conversion use the stock 944 fans AND radiator without issues. My feeling is that I've got enough potential cooling capacity. I've put a bleeder in the top radiator hose while I'm trying to get the air out of the system, but maybe that isn't my problem. It's also fairly chilly in Maine too.

-I haven't fiddled with the timing at all so that should be fine, I've changed the MAF so the AFR may very well be screwed up. I had the tables loaded for the corresponding MAF sensor, but it will have to be fine tuned. I'm pretty sure things will be in spec enough for now though. None the less I've ordered a wide band O2 sensor and will be installing that over spring break to see exactly what my AFR is.

-I've got a 30psi radiator cap installed

-I'm running 10w-30 RP

-Brand new so no blocked radiator, and the fans move somewhere around 8400cfm nominally.

-Again, I'm not running a t-stat. All I've got is a CSR neck, I didn't block any passages in the wp. Judging from the thread I referenced I feel like I may have a lot of water just re-circulating the block and not going through the radiator.

-My other problem that may be the issue is a lack of a vent on the top of the radiator. The Griffen had a cap, but I have a pressurized expansion tank with a cap as well. So I want to cut off the filler neck on the radiator (it's lower than the expansion tank) and simply put a plate over it and add a small nipple that will lead back to the expansion tank. The expansion tank is teed into the lower radiator hose, but I will also be changing that to a nipple on the side of the radiator. The steam tube from the front of the heads is leading to the pressurized expansion tank. The rear of the engine is lower than the front, the expansion tank is the highest point on the system.

Thanks for the help and patience!

 

Hi,
once again we chat! The 30# cap seems pretty high to me. ...... I think 15-18# will do the trick/could be wrong! If everything is circulating as stated the engine should be cooling efficiently for you..............remember the cooling system is pressurized similar to a pressure-cooker that mom uses. It allows higher temps due to pressure increase......i'm betting on the cap!!!!!!!!!!!!
Have a blessed day! Captain jim
PS: IT TAKES MORE HP TO DRIVE THE WATER PUMP WITHOUT A THERMOSTAT......

 

Hey, thanks for replying! Well, yes, with higher pressure comes a higher vapor pressure which reduces the boiling point. This theoretically would increase the temperature at which the coolant would start to boil and create problems, but I don't see how this would cause a hotter running engine? It would help the problem by allowing the coolant to carry away heat for longer before starting to boil, right??

Also this is the quote I was referring to above:

If it is the radiator cap we'll know as soon as I cut off the radiator fill neck and have just one cap on the expansion tank.

 

Can someone explain that? ->"IT TAKES MORE HP TO DRIVE THE WATER PUMP WITHOUT A THERMOSTAT".

I ran my racetruck without a thermostat a week ago. The temp stayed around 170* unless I forgot to turn my fans back on after a run. I blocked off the bypass port behind the thermostat and plugged both heater hoses. My temp sender is screwed into the top of the waterpump. Is that how it's done, or did I do it wrong? This is a race-only vehicle that sees no street time.

 

Any thoughts on this^? I'm wondering if maybe I'm not circulating coolant through the whole system...just the radiator and waterpump. It would've blown a headgasket by now if it was overheating right?

 

Luke,

If you can't run a t-stat because of fitment issues.......how about just slowing down the coolant flow to the radiator by adding a smaller diameter hose on the return radiator hose. Like use a valve of some sort in the normal radiator hose that has a stepdown outlet, then put on a length of smaller diameter hose, then step it back up to the radiator hose. Splice that into the upper radiator hose. That would basically be a rstrictor. You need to keep the coolant in the radiator longer.

And a 30psi cap is way too much....get an ~18psi cap.

.

 

Overheating without a thermostat happens sometimes. Use a restrictor plate somewhere to slow the flow down.

 

Can you find an inline thermostat housing (one that goes in the
hose) or maybe even fab one up out of (say) two SBC thermostat
housings back-to-back?

 

Just put a low thermostat in it and save your stuff.

http://www.summitracing.com/parts/MRG-6367/
This thermostat works with this( http://www.jegs.com/i/CSR/170/911LS1...oductId=756559 ) style thermostat housing for tight engine bays.

 

no thermostat would not cause an overheat.
If that were true then for normal applications with a thermostat when they do overheat and the thermostat opens fully (which resembles no thermostat... no obstruction... maximum coolant flow) the engine would continue to overheat. But it does not, it cools down. And if you were to slow down the flow of coolant in the radiator, you also slow down coolant in the block which will pick up more heat. So whether this leads to a cooling down or heating up of the cooling system as a whole would depend on the rate heat is dissipated from the radiator vs. heat input from the engine, which i don't have numbers for so can't honestly say. Maybe at idle with radiator fans on high, heat dissipation > heat input so it would cool down, but I kinda doubt it for an engine under load.

fact is if you need to slow the coolant flow down in the radiator then your radiator and airflow combination is undersized and cannot handle the heat output from the engine. The cooling "system" is simple, and it's a combination of radiator size and airflow, you can have a small radiator but will need massive airflow to make up for that. Flip side obviously is if you have shitty airflow then you need to increase the radiator size. Outside ambient air temp also plays a huge role, less than 50F air will cool much more effectively than 90F air in the summer. And regarding airflow cold air has to effectively make it to the radiator, through it, then out the engine bay for there to be flow and for the air to carry heat away. What can happen is a crowded engine bay can disrupt air flow where cold air hits the radiator but doesn't really flow through it as hot air builds behind the radiator and in the engine bay.

So if it's cold outside and your engine coolant temp is pushing 220F, your radiator piping should be around 200F at the top of the radiator. Try to measure it somehow, and if you have fans pulling air through the radiator with 220F coolant, you should be getting nice hot air out from the radiator. If your not then you have a coolant flow problem and the hot coolant is not making it into the radiator. Another way to check this would be to fab a piece of clear 2" or thereabouts vinyl tubing into the upper radiator hose to visually see coolant flow, just don't let it get too hot. I'm not that knowledgable about the cooling circuits at the waterpump where there are takeoffs for the heater core and stuff, maybe doing a loop there is disrupting flow in which case i would block off all unused nipples at the water pump. All you really want is input to the water pump from radiator, and output from thermostat neck to radiator.
At this point in time I don't think a 30psi cap is your problem, if anything it's prevent coolant boiling when you're slightly overheating. hope that helps.

also, don't know what you did for accessories and serpentine belt but do you have the water pump spinning the correct way?

 

The LS1 thermostat has dual functions which oppose each other:
- thermostat (opens when hot, allows radiator coolant to flow into pump inlet);
- bypass (tends open easier when TS is closed, tends to be hard to open when TS is open);

When the TS is closed, the BP allows coolant to circulate between the block and pump while engine is cold; it takes about 5 psi of pressure difference across the BP to open the BP (BP has pump low pressure/suction on one side, and high pressure on the other side); since the TS is closed, there are two paths for coolant: thru BP (pushing it open against the BP spring) and thru heater circuit (which is narrow plumbing, higher resistance).

When the TS is open, it pushes on the BP via a spring, and makes it harder for the BP to open, it takes about 10 psi pressure difference to open the BP; this causes coolant to flow out to the radiator (much less resistance than the BP) and return from the radiator thru the TS and into the pump inlet.

If you remove the TS (and the BP which is integral with the TS), then coolant has a choice of paths: thru the BP port and into the pump inlet (pump suction); out to the radiator; thru the heater circuit; the last two have higher resistance; with the TS/BP removed, the BP port is open, so the coolant goes thru the BP port easily, into the pump and back into the block; some coolant will still go thru the radiator and heater cores, but most of the coolant goes thru the BP port.

Coolant circulating mostly thru the block doesn't necessarily cause overheating, since when it gets hot it expands and pushes out to the radiator (convection current), but this is not optimally using the radiator.

See attached LS1 cooling system flow "schematic".

 

what the **** are you talking about joe ?

 

Ok, let's see if I can explain:

Old Geezer showed me a pic of a section cut he did on the thermostat/bypass pocket of the LS1 pump, and with closed TS the BP valve is already touching the BP port.

I measured the depth of the bypass port and compared this to the depth of the bypass valve on the end of the thermostat, the bypass valve is always in contact with the bypass port (i.e. the bypass port is always closed).

If you look at a TS, you will see that as the TS opens, it pushes on a spring which pushes the BP valve; i.e. as the TS opens, the BP will be pushed more shut (i.e. BP valve will be harder to open).

I measured the spring force on the BP valve and calculated the pressure required to overcome the spring to open the BP valve.

I also followed all the passages thru the water pump to/from the block and TS/BP pocket, and thru the pump impeller, and drew the flow "schematic" I posted above which shows coolant flow paths and the TS/BP relationship; when reading below, follow along on this schematic.

The BP valve is always shut; the end of the thermostat pushes on the spring which pushes on the BP valve; when TS is closed (moves away from BP), it takes about 5 psi to open the BP valve; when TS is fully open (moves toward BP), it takes in excess of 10 psi to open the BP valve.

Some BP valves have a hole in the middle, this allows some coolant to leak thru, but this is still a high resistance path.

When TS is closed, coolant from block has two paths: heater circuit, and thru BP (which requires 5 psi difference across the BP valve to open it); the HC has sufficient resistance to allow the pump to generate more than 5 psi pressure difference across the BP valve, so the BP valve opens, and coolant flows from block into pump (and some flows thru HC).

When TS is open, coolant from block now has three paths: heater circuit, BP port (which now requires at least 10 psi difference across the BP to open it), and radiator (which can now flow since the TS is open); the radiator has the least resistance of the three paths, so most of the flow is now thru the radiator, and some the the HC.

The TS is never fully open, so the flow thru the radiator is regulated by the TS; the TS also regulates the spring pressure on the BP valve (inversely with temperature).

Understanding what the BP valve does is the key to understanding what happens when the TS is removed. If you remove the TS, the BP valve is removed; this allows coolant to have three paths: HC, BP port (which is now open), and radiator (which can flow since TS is absent); so now the least resistance of those is the BP port (which feeds the pump inlet, so the pump draws from the BP port)... i.e. most of the coolant flows the easy path to via the BP port, thru the pump and into the block, and less coolant flows thru the radiator.

 

Joe,
So since I blocked off the BP and HC, my coolant goes through the block and flows to the radiator(restrictor installed in place of TS)? Right?

 

Yes, since you blocked of the BP, the coolant leaving the block goes thru the radiator.

 

Like this (see purple arrows):