UPDATE 8/2/09: Leak appears fixed! Finished installing the new radiator (NOS OEM unit from Corvette Recycling) and drain/partial flush/fill. Seems to be working well! Now to detail it. And put it up for sale.


ORIGINAL POST:
I have a coolant leak problem in my 96 LT4. I thought it was the lower radiator hose leaking and the connection to the radiator, but now I'm not so sure. I have purchased new upper and lower hoses and plan to do a drain/flush, replace these hoses, maybe a new T-stat (I have one from the previous owner) and then fill. But I want to be sure that I fix the right problem and don't loose my fresh coolant after I'm done.

After my drive to work yesterday, I checked under the hood and found coolant wet spots on the right side, top of the radiator area and on the body nearby. The lower rad hose also shows plenty of sign of being wet now and previously. I don't think it is the recovery bottle as it remains level once the engine cools. Today after getting to work, I didn't see any wet spots, but maybe it was low enough that it didn't leak. What is the best way to spot the true source of the leak WITHOUT having the pressure test tool for the system?

I also have a couple of questions about the drain/flush process. I have read my FSM.
1) can't get the radiator cap off. FSM says it is threaded and to turn 1/4 turn to release pressure (I can do this) and then screw it off the rest of the way. Nope. Won't screw off any further and it doesn't come off at this point, even with lots of wiggling. What's the trick?

2) FSM says after filling the surge tank with clean water, watch the two bleeded screws for a stream of clear water to know when it is full, then close them. Ummm...where? They are NOT listed in the the "Drain" process and they are not pictured in the FSM.

3) How hard are the knock sensors/drain plugs to remove? Unclip a wire and turn 'em out with a wrench? Do they have gaskets or o-rings that need to be replaced after removal?

4) FSM says to drop in a couple of leak stop pellets after the final fill. True? Can one get these anywhere, or a dealer item? Needed?

Thanks for any help! Finally going to try to tackle this over the weekend.

Rob

 

First off - I just replaced my radiator on my LT4 because the side tank on the passenger side was leaking - so don't rule out the radiator itself. As for the other questions:

1) Push hard and turn. IIRC you should be able to look under the cap and see the arrangement that is keeping the cap on.

2) LT4 only has one bleed screw. Spent a lot of time looking for that phantom second one a few years back. Look near the thermostat for the one you do have.

3) Easy to take out. Just put 'em back in. The electrical connectors are tricky. You have to squeeze them to get them off.

4) I have never used leak stop pellets, and haven't ever heard anyone say they were a good idea. I don't like any kind of "leak stop" in anything.

I was actually just finishing installing the C5 brakes on my car just recently, still up on jackstands, and discovered a little puddle of coolant under my car. Luckily I had a NOS radiator already.

 

I just found a leak on my 96 after it started leaking at a road course this past weekend. I pushed sideways toward the outside of the car on the hose where it goes into the radiator on the passenger side and coolant started leaking. The plastic is cracked and I ordered a new one to replace it.

 

When you say do you mean the hose is cracked and you ordered a new hose? Or is the plastic something else that you ordered one of? Thanks for the clarification.

Rob

 

No. I'm sorry for the confusion but the outside of the radiator is plastic and it is cracked so I had to order a new radiator. At first I thought it was the hose leaking but it is the radiator.

 

Check the weep hole on the bottom of the waterpump. It drips on the belt and splashs the coolant under the hood.

You used to be able to get the tablets from the dealer. I used to use them, but haven't for many years now.

 

Here's a leak it took me a while to find on my 96. The body of the inline check valve in the heater hose developed a crack. It must have started out small and slowly gotten bigger. I finally found it when it got big enough to shoot a stream which hit the exhaust manifold. Even then it was intermittent.

 

Check the water pump first. There is usually coolant on the belt as has been mentioned.

Also check the heater hoses. I had a check valve leaking a few months ago. I replaced all the hoses.

 

I will check the water pump, but it was replaced, along with the Opti, by the previous owner not long before I got the car (3 years and 5k miles ago).

Based on where I see coolant and evidence of evaporated coolant, the leak appears to be in the front passenger side near the radiator. Where are the check valves in the heater lines? Is this under the hood, or deep into the car where the core is?

Thanks.

Rob

 

I had a leak that turned out to be the right-side rad tank as well. A new OEM radiator from GM ended up being cheaper than having a new tank put on the old one. Didn't leak much, and the crack was hard to see, especially while still in the car.

One thing I did while changing mine is to reverse the 6 clips+screws that attach the two halves of the fan housing so that they can be reached from the outside/front of the car instead of having to deal with them down in the front wells. Just in case I want to pull it apart later for cleaning...

 

The valve is actually a flow control valve to limit pressure on the heater core at high rpm's. The valve is in one of the heater hoses near the #6 plug. The valve is black and only about 1" of its length is visible.
Mine failed at a very bad time and blew coolant all over the engine compartment. There had been a slight, intermittent odor of coolant for months and I hoped it wasn't a leaking heater core. The odor cleared up after the failure so the flow control valve must have been weeping for some time.
Cost was less than $20 at the dealer. Take care to orient the new one the same as the old or it defeats the purpose.
Good luck.
BTW, the knock sensors shouldn't be too tight. One of mine had the hex messed up so a big set of channel lock pliers was needed to get it out. Replaced it too.
After flush and refill, the temp will be erratic (especially the analog gauge). As you've likely read, the FSM recommends against "Aggressive maneuvers" until after 3 full hot/cold cycles. I've flushed my '95 3 times over the years and twice had no big temp swings. Once was a bear; had to shut the engine off at 260F twice then 5 or 6 days of gentle driving. Eventually settled down. This even after bleeding the ONE screw carefully.

 

I did the same thing when I replaced my radiator - I'd like some of what whoever designed that shroud setup was smoking. Maybe GM had to come up with jobs that could only be done by members of the Midget Contortionist's Union.

 

Well I found the leak and it was NOT just the hose. After moving it into the garage and up the ramps, I had a good bit of coolant and it really looked like it was wet about halfway up the right side of the rad.

After draining and pulling both radiator hoses (I was going to replace them anyway), I examined the lower and didn't see any sign of damage or failure. I also found that the lower hose I bought was way wrong...a good 8" too short and the wrong bends. Grrrrr!

So I decided to pull the radiator. After fighting those dang little bolts for an hour or more, I finally got it out and examined it. Like Toy90 and TravisD, the right-side plastic tank was cracked. One vertical crack just inboard of the lower outlet and one about halfway up. Will need to let my fingers do the walking on Monday to find a new one.

I DEFINITLY will be reversing the lower 3 clips on each side so they are removed from inside the intake area in the front! Taking out the AIR pump and getting to all of them was a real pain!

Rob

 

Leak appears fixed! Finished installing the new radiator (NOS OEM unit from Corvette Recycling) and drain/partial flush/fill. Went for a drive (it is almost 90 deg today) and it only got up to around 202, so it is really cooling well (clean, new radiator). Seems to be working well! Now to detail it. And put it up for sale.


Rob