Langadorf

I have an 383 LT1 motor from a 94 Camaro installed into a '79 vette. I'm running GMs dual plane carbureted intake with all new cooling accessories.

The problem I'm running into is that if I idle long in traffic, a drivethrough, my driveway, etc., it creeps up to around 200ish. Now I know this is considered normal for an LT1, but once it gets above 185-190, the car runs like crap. It'll still move but has no power until it cools back down. If I'm crusing at >30mph its fine, but once I slow down it starts heating up again. If I stop the motor when its this hot, I can hear a bubbling sound sometimes coming from the engine. This problem has always been present since I installed the motor 10 months/3000 miles ago.

My oil and coolant both look good so I'm not suspecting a blown head gasket or anything like that. There are no coolant leaks that I can tell. However, after driving for several days or letting the car get hot, the coolant level is definately down some.

Here is a brief rundown of the cooling system:

* Radiator - There is absolutely no debris or anything blocking the radiator. I have a small trans cooler in front of the radiator. The radiator was new when I installed it, which is about 10 months 3000 miles ago. I'm running mostly purified water with water wetter and a little anti-freeze. Have an 18lb radiator cap.

* Fans - I'm running flex-a-lite dual electric fans (2 12" flowing 2500cfm) which are always running when the car is on.

* Thermostat - I have tried both the stock 180 deg thermostat and the hypertech 160 deg one. The 160 deg stat just seems to keep temperatures under control for a few minutes longer before it heats up again.

* Water Pump - new stock LT1 water pump. 10 months old/3000 miles.

*Hoses, etc. - The radiator hose off of the thermostat coupling on the pump goes to the passenger side of the radiator about half way down. The large return hose (driver side, about half way down) goes back to the water pump with the little branching throttle body hose blocked off (carbureted). The smaller return hose (driver side, bottom) goes back to the water pump. I have heater/AC removed, so the heater core hose just loops back to the water pump. The head-head coolant line is connected and the attatching hose runs to the radiator near the cap. I have a small hose running from under the cap to a catch can.

* Engine block/heads - The whole thing was apart before I assembled and installed it so I have no reason to suspect any clogged passageways or anything like that.

Anyone have any ideas on how to keep it cooler? It seems to run cooler in the winter time, but in summer it just wants to get hot. I'm in Texas so its hot 8 months of the year.

Also, any ideas on why it starts running poorly around 200 degrees? I know the EFI LT1s are supposed to run around this temperature and seem to run fine.

Is it normal for some coolant to evaporate over time? Would coolant levels change from one time to another? Or should it always be where you left it?

The only idea that I have come up with is that as the car gets hotter, more heat comes off of the headers, which is taken in through the carb, which heats up combustion, heats up exhaust, heats up cooling system et al. However, if this were true I'd think I'd run into detonation problems (11.7:1 compression) etc. Plus, all the older carb'ed motors never seemed to have this problem.

Full engine specs below. Any input would be appreciation.

Thanks.


[Modified by Langadorf, 8:05 AM 7/7/2002]

TIMSPEED

With almost 12:1 compression, I assume you're running at LEAST 93 octane in that puppy right? I would say 200º is PERFECT for a carb'd/strok'd/12:1 LT1 motor! As for it running like crap..I would guess it has to do with the tuning that has been done. At higher temps it may be leaning/fattening it up. I would invest in some dyno tuning time if I were you. Also, you may want to contact Speed Demon motorsports to help you out with some stuff. They do some good stuff to LT1's.
*EDIT* - It's late and I'm tired..I just reread your post...about the detonation..I'd bet you ARE getting detonation, but your sensor's are picking it up and changing things around, hence it running crappy. I would try some 100 octane race gas...see what happens.


[Modified by TIMSPEED, 3:40 AM 7/7/2002]

Langadorf

Yes I'm running 93 octane gas. I've even run higher sometimes to see if it made a difference.

I don't have any knock sensors or computer. It's a carbureted setup. The only sensor I have installed is an A/F monitor that I installed. Even when it starts running crappy, it's still better than a 14:1 ratio.

I don't hear any detonation at all when it starts running crappy. It just seems to lose power.

kaiser

Maybe there is an air pocket in the cooling system. Do you have a high-point vent, so it can be 'burped'?

Also, did you double check the various hose routings to make sure you aren't bypassing the rad (or something else important)? Didn't the Camaro LT1's use a shut-off valve in the heater circuit? Are you using the LT1-speciic thermostat?

HTH



[Modified by kaiser, 2:15 PM 7/7/2002]

KLLRVET

Are you sure that you aren't getting a head gasket leaking into the combustion chamber? That's what it sounds like to me. That may explain why it runs poorly when it gets hot (pressurized).



[Modified by KLLRVET, 11:44 PM 7/10/2002]

Langadorf

Kaiser:I've used the air bleed and no air is in the cooling system. The radiator/hoses/pump are all routed correctly from what I can tell in comparison to LT1 camaro/vettes I've looked at. I don't have the heater hooked up at all so I won't have any sort of heater shut off valve. Yes, I'm using the LT1 specific 'stat.

Kllrvet: Wouldn't all kinds of weird stuff be in the coolant amongst many other things?


[Modified by Langadorf, 5:08 AM 7/8/2002]

KLLRVET

I don't know from experience, but from what understand, no. I think you can "read" your spark plug to see if coolant has been burned in the combustion process.
Tony


[Modified by KLLRVET, 12:10 AM 7/8/2002]

Langadorf

I changed the plugs yesterday and didn't notice anything odd about them. Slightly carboned up (I've been running it a little rich) but nothing else.

DOCTOR J

Langadorf

I suppose you have tried all the obvious (brute force) stuff: Removing the stat completely; checking the pump coupling to make sure it's turning; pinching off the heater hose, to see if that directs more coolant flow to the radiator. So there must be something else going on - Anything unusual in the oil temps?

On hose routing, you might check with John Millican - he does the LT-1 intake conversions to small blocks (posts on the 3rd Gen TPI board). I think he had some issues with how to route LT1 coolant correctly, but I don't recall the details. Was your carbed intake designed for LT1 heads?

On cooling fans, Monte Wiliams (on the Engine forum) swears by Spahl (?) fans, and he tested quite a few kinds. You might touch base and see what he thinks of your system. IIRC, he rejected the flexalites as not having sufficient capacity.

For the engine itself, since there is no computer, what is controlling the spark curve? Who set up the curve, and how was it checked? Is it using Vac advance? What triggers the MSD box?

If an ordinary small block were running too hot, I'd first wonder if it had too little advance in the timing curve; or it was too lean (or had intake flow distribution problems). Is your air-fuel meter using a heated sensor? If not, your readings could be bogus - a dyno with a WB would show that up right away. Are all the exhaust ports evenly hot?

One last thought (reaching waaay into the past) - does that manifold have some kind of heat riser? Back in olden times (before Fuel Injection & engine sensors/computer diagnostics) hot running problems were sometimes caused by fuel cooking off in the carb bowls. Keeping the feed line away from the exhaust, and (thermal) insulating carb spacer sometimes helped there.

Coolant doesn't evaporate from a properly closed system. If it's not leaking out the front or the top, it has to be going somewhere. If it's not in the oil, then there is only one other place for it to go...

That's all I can think of - hope some (or any) of it helps. Good luck.

PS - I keep coming back to your heater bypass - I don't know what a Camaro heater circuit looks like, maybe it's totally different than an L98 Corvette - but on mine, if I just replaced the heater system with an open hose, I would be bypassing about 15% of the hot coolant around the radiator. That would cause a temperature problem. Are you sure your engine is confugured differently? If so, just ignore my ramblings.




[Modified by DOCTOR J, 2:32 AM 7/8/2002]

weekendwrench

How about checking to see if you are getting the fuel too hot before it goes into the engine. Are the fuel line run near the headers? Any possibility the fuel is boiling? What kind of fuel pressure are you running?

Is the manifold you are running made to work with these heads? Any possibility you are developing a vacuum leak as the engine warms up?

If you are loosing coolant you definitely have a leak somwhere. Get a radiator pressurte checker or have a shop pressure test your system. Here is a link to a pressure tester in case you are not familiar with one.
http://cgi.ebay.com/ebaymotors/ws/eB...tem=1841701514

Langadorf

Doctor J: Thanks for all input. Alot of good ideas.

I haven't tried removing the stat completely, but have tried 2 different stats so I'm sure its working. With the cap off I can see coolant flowing in from the head-head coolant tube, so I take this as a sign the pumps fine. The heater is disconnected so the heater hose just makes a loop back to the water pump. I don't have an oil temp monitor, but now that you mention it I'll look into getting one.

The intake is GM's own special LT1 carb'ed intake manifold (https://www.spoperformanceparts.com/store/catalog/Product.jhtml?PRODID=1002&CATID=995) . It has no coolant passageways. The coolant flow should be the same as a typical LT1.

These fans seem to move lots of air - even more than what I've seen in stock LT1s. I've sent Monty Williams an email regarding this however to see if he has any additional input.

An HEI distributor is controlling the spark curve (fixed timing + springs/weights for advance). The MSD 6AL is able to read the output from the distributor and trigger the ignition events. Originally a local performance mechanic set the curve (w/out vac advance), but it kept knocking at part throttle, so I adjusted the distributor just to the point prior to detonation. I have tried retarding it some, but performance just goes down. Since then, I have tried using and adjustable vacuum advance (both manifold and ported vacuum) and it may have helped cooling slightly. However, with any vacuum advance hooked up, I have to retard total timing (to avoid knock) to a degree where it hurts performance. So currently vacuum advance is disconnected. I may try it again and have to live w/ the performance hit.

The O2 sensor in my A/F monitor setup is heated, so I don't think I'm running too lean. The driver side header seems to cool to the touch quicker than the passenger side. I couldn't say from port to port though.

If I'm leaking coolant through a head gasket into the combustion chamber, wouldn't there be some sign either in the coolant or on the spark plugs? The spark plugs look normal if slightly carboned up (replaced w/ new yesterday). The coolant has some small flecks floating around in it (dark colored, black/brown).

Again, thanks for the input.

Langadorf

That's one possibility I've thought of before (fuel boiling), but I'm not sure what I could do to check it. The fuel runs in a steel tube past the headers, from where it's connected to a rubber hose that runs a good bit in front of the headers up to the carburetor. Near the carb I have another fuel line running to a pressure gauge mounted near the winsheild viewable from the driver seat. Fuel pressure typically stays around 6PSI.

I've run a vacuum gauge on it when it's hot and I've not seen any drop vs. cold.

I hadn't thought of getting a pressure check. I'll have to do that and see what I find.

Langadorf

This is how I have the heater bypass hose hooked up. Is this causing a problem?

Also, anyone know what the purpose is of the smaller tube on the lower right portion of the pump?

I'll have to give the no stat option a try.

The ignition and engine in general runs normal as far as I can tell so I wouldn't expect it to be that polarity problem.

When I swiched plugs the other day, I wouldn't say any were "steam cleaned". They all had some degree of carbon buildup on them.


[Modified by Langadorf, 9:26 AM 7/8/2002]

DOCTOR J

Nice pic.

Your bypass is taking some coolant from the high pressure side of the pump - and sending it right back to the low pressure side of the pump. That water never gets to the rad, so it never gets cooled - it just flows in a circle.

It's sort of like trying to fill up your bath tub with the plug out of the drain - the water is moving around, it just doesn't stay where you want it.

Take a pair of ViseGrips and go pinch that hose. If your cooling problem goes away, you found the problem.

Re the ignition, have you put a timing light on the mechanical advance to see what it's doing? Try switching the low voltage leads anyway (they throw the timimg signals off - there is a section in Chris Jacobs' ignition book that describes the zero-crossing effect in some detail).

Re how to set vac + mech advance I saw a tech description not too long ago, might have been on the Scoggin-Dickey site. If I see it again I'll send the reference along - not many peeps know how to do that any more.

Later


[Modified by DOCTOR J, 3:53 PM 7/8/2002]

85 Dave

Get rid of the coolant bypass hose, and put plugs on each end. I've bought them from Autozone in the past. Also, if the head gasket is leaking and letting combustion gases into the coolant, it will cause overheating problems. There is a dye you can put in the radiator that changes color in the presence of exhaust gases.

Langadorf

Can you get this dye at the local auto supply store? What's it called?

85 Dave

Some of the bigger parts stores should have it, or be able to get it. Don't know the name, but call them first. They'll know what it is.

Langadorf

I've called around to most of the part stores in town and nobody has heard of anything like that.

Langadorf

Well, I tried clamping the heater hose w/ ViseGrips but it didn't seem to make a difference. It still heated up to 200ish and stopped. I was thinking about just blocking off both ends to see if that helped but now I'm not sure.

Once the car cools down (probably tomorrow morning), I'll try pulling the tstat to see if that makes a difference.

After that, I'll play w/ vacuum advance again and that polarity thing, but if I don't have any luck I'm gonna pull the heads to check for a gasket problem.

Any other ideas?

Thanks.


[Modified by Langadorf, 1:34 AM 7/9/2002]

95BLKVette

I've said it many times and so have fellow 383 owner's, the stock Corvette single row radiator does not have the colling capacity for a hopped-up 383 :U

My solution is shown in the lower photo in my profile....works like a charm :D

Lowered my temps 30 F on average...and no more stop and go overheating :cool: :cheers: