I had taken an LT1 engine form a 96' Camaro and placed it into my 76' vette. Now it stays at 180 @ idle but steadily increasses to much hoter, 220 when you start to put stree on the motor by driving it. What is causing this problem. I had opened up the bleeder valves (one before the thermostat and one after the thermostat) and made sure the hoses were positioned correctly since it's a reverse flow pump. Need help.

thanks

 

The temperature sensor in your 76 is in a different place than it is in the Camaro, so you shouldn't expect the coolant temp to be the same as the original engine which had the coolant temp sensor at the output side of the stat. The thermostat begins to open now when the INLET temp gets to 180 (or whatever stat you use). The inlet to the stat takes coolant FROM the radiator, and your temp sensor is in the block or head, so the 76 sensor will always be higher than the stat opening since the stat can only deliver 180 coolant to the head (close to your coolant temp sensor). 220 temp at the head is a nothing and is of no concern. Remember your coolant system has a pressure cap and the coolant will not boil until well over 260 F and if you see 260, shut the engine off and let it cool down. Anything below 260 is nothing to be concerned about.

 

cli59vette,

Wow, that sounds like an awsome project (LT1 in a 76)...

It sounds like the thermostat is working correctly, but that either the engine is generating too much heat, some blockage is occuring (air?), or the overall cooling system is under-rated for the engine.

What radiator did you install? Does it have the BTU cooling capacity for an LT1?

Did you also install a 'surge' tank (higher than the engine), to which the rear head 'vapor' pipes must be routed?

What pressure and location of the 'radiator' cap?

Any chance the engine is running lean due to: injectors, o2 sensors, exhaust leak fooling the the o2's, exhaust back-pressure 'substantially' different than OEM design? Once up to temp and in 'closed loop', consider using an exhaust analyzer to see if the mixture is truely correct or may be lean.

 

Thanks for all the input. I wanted to clarify that I did this project many years ago before I new what I know now. I had converted the intake from the EFI to a carb set up. I used a new copper version of an existing style radiator (to fit the 76) but no one really stressed to be btu cooling ability and have the same over flow tank still in place as original. The pressure cap is located on the passenger side top and is rated for 18lbs. My thermostat lead is in the same location in the block which could be incorrect to what is OEM. The thermostat does open up because I see the coolant flowing.

As far as the two ports in the back of the heads, I have them routed to the outlet hose off the water pump as directed from another post as to how it was originally set up in the 96' camaro (but maybe this is wrong to?) So what do you think, how can I fix the problem??

Chris

 

Got to ask how was it working after the original install?

If this problem just happened now, even though you see flow the stat might be tired and not working correctly. I would change it out first before looking for complex problems.

And is it a possibility that after these years the radiator might need a flush and cleaned out.

 

You really don't have a "problem" to fix. Drive it.

 

Ok, Badduck, why do you say I do not have a problem? Before the swap the car ran just fine. When I started to restore it a little, I replaced the engine and radiator.

And I had already replaced the thermostat twice??

I am just afraid to blow something and cause even more problems!! So what's the concensous. I was going to give it a test run soon.

Thanks again guys.

 

You will find that the LT1s run much warmer then the old school small blocks.


Heck I don't even think the fans kick on full speed on the Lt1 Vettes until somewhere around 225 deg.

 

Not intending to provoke an argument with you at all, but mine runs 174 and it was 101 degrees outside here yesterday !!

Lots of potential causes, I'll mention some un-commonly discussed ones.

1) pull the gooseneck of and grind away the castin flashing on the i.d. where the straight part meets the dome.

2) inside the WP I removed from mine when I did a swap, I saw in one of the ports that feeds the left bank, there was a painfully large hunk of cast flashing smack dab in the middle of the orifice way down in there. Major blockage from GM - I estimate it covered 40% of the cross sectional area.

3) on my current block and the one on the stand the bend in the block where the H20 enters it has a huge ole slug of slop in there.

Not all engines may have these, but I think all do, more or less. The gooseneck is an easy one. I opened that babe up to one inch dia. and noticed a difference in the cooling. Your mileage may vary on these suggestions.

 

I guess you could have a vote if you want but that won't necessarily get the correct answer.

LT1 motors were designed to run at the temps you describe. Fans first come on at 228* in factory cars. Do a search and read up on the engine specs. Changing stats will make little difference.

 

Just want to ask one last thing. As far as the two vents in the back of the heads, was it correct in attaching the line to the outlet side of the thermostat? This is what I was told once before on this forum. Or should it be attached/relocated a different way? Thanks again guys.

And I'll post back again, will drive it a bit and push it, see what happens. i gues the worse thing (and tell me if i am wrong) is a hose blows off from pressure or the relief cap opens and coolant comes flushing out. I'll let you know soon enough.

 

cli59vette,

I've no knowledge of the LT1 install in other than the Vette, but here's my thoughts with that in mind:

Since you did this a few years ago, I presume the increase in temps is a recent problem, so I'll focus on things that might change or could suddenly become a problem as components age..

re: the radiator -- since it was new at the time, and although aluminum is lighter and better at transferring heat, older copper radiators are likely double channels (whereas current LT1 aluminum is single channel), so chances are it has a similiar BTU rating as the more current LT1 single channel aluminum radiators.

Presume your 'overflow tank' is a non-pressured plastic tank which is mounted somewhere below the radiator cap. Further presume the level in this 'overflow tank' is not increasing during the 'increased temps'. If it is, then I would suspect the radiator cap as being unable to hold in the 18 PSI pressure it is rated at..

How many cooling fans (figure at least one between engine and radiator)? Are they working at correct speeds and at correct temps? Many current cars actually turn-off the fans at highway speeds as it can actually slow-down the air passing through -- any chance a change to the fan control systems might have effected their operation?

Not sure what you mean by "My thermostat lead is in the same location in the block which could be incorrect to what is OEM".

Vette LT1's have a unique water-pump which is connected to each head (the intake is actually dry), and a unique thermostat (has an extra plate on the bottom which opens/closes an internal passageway) and is mounted in the top of the water-pump and connected to the radiator's lower hose.

What's unique about the LT1's is its 'reverse coolant flow'. I.e. cool water flows from the lower radiator hose into the water pump at the thermostat, is 'mixed' with hot water already in the engine, and then routed to the heads first, followed by the block.

This 'mixing' reduces cool water 'schock' to the heads.

However, the 'vapor pipes' on the back of the heads (in the Vette) have water 'coming out' (not in), presumably it is just a little bit of the water which is directed to the block to 'siphon off vapor', so that any vapor which occurs as head heat vaporizes coolant, it can be directed to the 'surge' tank and 'scavenged'.

If you don't have a 'surge' tank, then the output of the 'vapor pipes' should be routed to the radiator via a 'T' into the upper radiator hose (in older cooling system designs the radiator is the 'scavenging device').

If the 'vapor pipes' are not routed correctly, and the anti-freeze is old (3+ yrs), the anti-freeze might no longer prevent 'spot boiling' 'air pockets', which can quickly grow to flow-blocking bubbles and cause increased engine coolant temperatures, especially in the heads, where the LT1's 'analog' coolant temperature sensor is mounted (passenger side).

 

Theadmiral94,

Thanks for the input. To help clarify a little more. I change the fluids and flushed the radiator last season. Also, I have two electric fans that run all the time behind the radiator pulling air and they equal about 3000cfm together. My overflow tank is the original plastic one that came in the 76 and is parrallel to the radiator cap. When the temp gage starts to climb, no extra fluid is pushed into the over flow tank. And I have the thermostat leads connected to the port that is on the driver side below the heads (in the block itself). I never actually chaged it from it's location, just put a new sensor and lead on for the thermostat.

I'll add this also. When I start the car, it will stay around 150 for a good 10-15 minutes, then it'll climb to 180 for a good 5-10 minutes, then it'll keep climbing where at 200 I just shut the car down because I do not want to cause any more damage.

so what do you think.

 

As stated before, 200 isn't a problem at all. Stock, the fans don't even turn on that low unless the A/C is activated.

I have (I believe I still do) a long technical article that explains the cooling system on LT1 engines, how it works, etc., that may help point you in the right direction. If you want it, email me jcameron266@sbcglobal.net

Jake

West Point ROCKS!

 

I'm a complete "know-nothing", but my '94 vette sat and idled ok(temp-wise), but when you drove it (it) went hot in a hurry. Found out the spline connector in between the camshaft and water pump slipped if the rpm was increased...

 

Thanks for the imput. I'll be test driving it over the weekend and will let you guys know what happens.

 

FWIW, I saw 167 digital temp on my 93 LT1 while cruising on I-35 today, outside temp read 80. Running 160 stat. It read 174 when it was 101 deg outside. These things cool just fine if you keep em moving and remove restrictions in system, see my comments in post above. Problem is when stopped in city traffic, but the Ecklers switch solved that one for me.

Car has been hiccuping ever so slightly, feels like electrical misfire. My spidey senses tell me its the throttle position switch. Dang, I hate it when I know something is about to go out....