I need some help here,

I just finished my LT1 Intake swap onto my LB9 (305TPI). But, I am having a confusing issue with cooling the thing. Know this part though, I am in Germany and seeing temps as cold as minus 15* Celsius outside in the morning.

1 - First the dash guage is pegging well beyond the 240* mark. But about the time I think the T-stat is opening the guage cools off all the the way down to normal. Then heats back up and fulctuates all day long. With my new TFS heads I had to use an adapter fitting to make the stock guage sensor fit into the driver side head. I used JBweld to hold the adapter fitting to the sensor and RTV to seal the whole thing into the head. I know this sensor is just a resistor that changes with temperature being a one wire sensor and all. So would the JBWeld be causing and artificial resistance and the guage reads high as a result?

2 - The ECM temp sensor is reading normal temps through my datalogs with tunerproRT - standard time to warm-up the engine - not getting hot enough to trigger the fan until sitting in traffic. THe fan is coming on when commanded by the ECM to do so.

3 - The two 3/4in hoses that are run to the remote T-stat housing are carrying the heat to the T-stat and in normal time the T-stat opens. When it does I see the radiator put off steam, which I think is condesation on the radiator from the night prior. I might be mistaking this steam for the radiator cap opening and venting coolant.

4 - There is no coolant in the oil and the system is not losing any coolant that I can tell.

5 - The radiator cap is popping open. Occassionally with-in a normal amount of time to warm-up the car, say a ten minute drive to the gas station, I hear water boiling and the cap blowing coolant in the overflow tank. I only hear it when stopped and only after the intial warm-up for the day. When I let the system cool in the parking lot and start up again the system holds pressure and runs fine all day. Only with the guage acting on the fritz as described above. The cap is original - 1991 vintage and I am thinking of replacing it.

6 - I have an innovate AFR sensor in the passenger side header, and the stock O2 in the drivers. The engine is fat rich (11.5:1) until the ECM starts correcting for the O2 readings. Most AFR readings at cruise are 14 to 15.3 which I understand as normal for this ECM.

7 - The plugs are a little bit hot for the set-up. Inspection shows no graying/browning of the porcelin and only black soot on the gound strap and body. I think two stages cooler would be perfect.

8 - I am not getting any pigging on the dataloggs and I don't hear any either. The engine pulls smoothly all the way to 6K. Although the headers make it hard regardless, they are loud. I have a full exhaust on the car.

Here is the back ground of this engine. Solid 30K on the engine and from the factory, I am the second owner and the engine has never been apart and never had any issues in its life until now. I did this all at once. New TFS 175 al heads, comp cam, Hooker headers 2210s. The intake I did myself, LT1 drilled for the dizy, redrilled all the bolt holes for the SBC intake bolt pattern, welded up the old LT1 bolt pattern, drilled the rear coolant passages for the 3/4 hose fittings, drilled and tapped front passenger side for the ECM coolant sensor to match up with the coolant port in the head. I used thin al sheetmetal to block off the front driver side coolant port and the EGR ports in the heads since I was not going to run any coolant from the front of the intake anyways. This way there was no chance of the intake gasket spilling coolant in the lifter valley. I will add that the head gaskets are from FELPRO pn:1094. The motor makes very good power and runs well to 6K, baring the bad tune.

The 3/4in coolant lines run straight to the remote T-stat from the rear of the intake manifold. The drivers side hose, which is the same side the temp guage is mounted, has a T-fitting allowing the coolant to pass to the Oil cooler then to the heater core, then to the radiator. This hose is also 3/4in and until the T-stat opens is the only way the coolant can get back to the radiator.

I am going to run the oil cooler hose from the T-stat housing and get rid of the T-fitting in the drivers side coolant line. I think this will push all the coolant from both sides of the engine past the T-stat and help get rid of any hot spots I might have. I also suspect a leak at the coolant guage sensor - hense the erratic readings due to the changing resistance.

Any one who has done this mod before had this issue? Any other ideas could really help.

Brian

 

Well, to update this thread here is what I did to the car.

I rerouted the oil cooler hose. It now starts at the remote T-stat housing and runs to the oil cooler, then to the heater core, then on to the radiator. I even double checked the timing and it was spot on.

The results were not entirely inconclusive. The temp guage still goes hi (+220) and the ECM temp sensor reading in my datalogs at the same time shows nothing higher than 50 degree Celsius/122 deg F. The good news is the temp guage does not go into the red anymore and once the engine is warmed up the needle sits around what should be 190degrees F, which is where the T-stat should open. I am starting to think the guage is accurate and the ECM temp sensor is bad. which means bad things since the temp guage has seen better than 240, although it has never pegged the guage, still a hell of a lot hotter than I want for a fresh engine.

I pulled all the plugs and found that the front 4 cylinders of the engine are running leaner than the rear 4 cylinders. The #3 cylinder was the leanest showing some soot on the ground strap and a bleach white porceline telling me a lean condition or potentially no fuel at all. I am going to reinstall my stock injectors and new plugs. I have no way of testing my new 30# injectors to see if got a bad batch.

An interesting observation here. my #3 spark plug is the leanest reading plug and the guage sensor is installed between the #1 and #3 cylinders.

Brian

 

i have a 400 with Dart`s pro 1 and home made Lt1 intake, I have no problem with overheating, to be honest during driving even in hot summer like this year-i`m from Poland, i was not able to get the temp higher than 95deg C, the car is running 12,5 at idle, but 14-15,2 at crusing. I would personally check both of the temp sensors, just take an OHM meter and check the resistance on cold engine-compare with the table, and do it when the engin is hot.
I`ve heard abt problem with lean rear cylinders after LT1-genI conversion, but only when engine is high rev. I belive 30# injectors are a bit to big for you, i have them in my 400 engine and a still can make 11:1 at 6000 rpm ,

brgds

 

Update to this,

I had to add in a 3rd 3/4in hose to the system. So the basic routing of the coolant goes like this.

Two hoses from rear of LT1 Intake to the remote T-Stat housing.
A third hose from the T-Stat housing down to the oil cooler, with a hose from the oil cooler to the heater core. The coolant then is routed from the heater core to the radiator.

The engine is now steady at 193-195*F all day. I do have the fan set to come on at 197*F in the chip. Routing the coolant through the T-Stat housing was what it was. Now all the coolant circulates past the t-stat before being bypassed to the radiator. Before, the T-stat was opening too late and certain hot pockets would form in the engine. hense the high reading temp guage.

Also, I had to relocate the CTS for the ECM to the remote T-Stat housing. And I think the old sensor I had was bad. So I put a new sensor in, mounted it in the T-stat housing and the two coolant sensors were matched up. Everything works now.

Hope this helps someone else trying to solve a problem.

Hotrod

 

The problem with your CTS was it wasn't grounded properly. With the adapter, JBweld, and silicone, there isn't a proper path to ground. You could have fixed it by soldering a wire to the outside of the CTS and properly grounding the other end.

 

To everyone, thanks for the help,

In summary, I had used RTV to seal the CTS that was also installed in the wrong location [pass cylinder head] giving the ECM a low temp reading. The #30 Siemens injectors [Ebay purchase] were not very good. I had several lean and rich cylinders. The T-stat bypass hose was in the wrong location for this set-up. The temp-sensor [dash guage] was found to be accurate once the CTS was moved to the remote T-stat housing. They match now.

What fixed everything?
The CTS got moved, still used RTV though.

I bought new injectors, #27s from South Bay Injectors. They have awesome service and cured my lean/rich problem instantly with the swap. The quality is what matters.

I had used a T-fitting in one of the hoses coming from the rear of the intake redirecting the coolant through the oil-cooler instead of forcing all of it through the remote T-stat housing first. Basically not all of the coolant was flowing past the Thermostat causing a delayed opening and elevated engine temps. To fix it I drilled another hole in the housing routing all the coolant there then to the oil cooler and so on.

I should have made an aluminum template from another intake, particularly a Vortec style intake due to the bolt pattern of my heads. I spent considerable time filing the mounting holes IOT get the bolts started during installation. The way I did it was to measure it out and lay the gaskets on the intake, center punch then drill. Took longer and now I know the rest of the story.


The engine runs great, dyno'd it two weeks ago. Ran all day then pulled us home (3 hr drive to/from) average speed was above 120mph on the autobahn. Never went above 198*F even after a sustained pull to red line at 5800rpm on the dyno.

This is my first engine, first time at a dyno, 305 SAE HP at the wheels from a 305ci and plenty happy. Tq was at SAE 302ft/lbs. I still think I am down on power compared to a stock LT-1. But I don’t have any timing above 28* @WOT and a richer 11.25 to 1 AFR. We couldn’t find the knock threshold so proceeded cautiously.

I'm done with this thread guys, the car is 98% complete, just some drivability tuning to do and some rattles to chase down. This LT1 mod has been interesting and very challenging with the welding & cutting of the bolt holes and then lining up the distributor hole. Not to mention all the other little changes that took forever to finalize.

The next one I do will be much better and not take nearly as long. Hopefully I'll be in the States by then and able to find a shop that can powder coat it.

Hotrod