ridiqls

Hello, I'm gonna check out a 94 z28 with around 140k miles on it. It failed a block test so there is combustion gases getting into the coolant. The owner has replaced the water pump and it is still overheating but able to drive for a few minutes.

What are the chances that the actual block is cracked or anything on the bottom end needs rebuilding in this case? I will check to see if there's water in the oil but based on initial conversation, the car drives and he drives it about once a week for 20 mins or so.

If it just needs the gasket and/or heads need machining then I will do the job myself. But if the bottom end is a problem, the cost of rebuilding an LT would be in the thousands and not worth it.

I've heard the stock block can handle a lot of power and is quite strong but want to gauge what the risk here by picking up this car.

slowpoke96z28

IDK a non intrusive way of determining one way or another. I do know I've heard of LT1 blocks cracking. if he's still been driving it and all it originally had was a warped head that "blew" the head gasket, there's a decent chance the block is cracked by now IMO.

ridiqls

I ended up buying the car but still troubleshooting and testing it. So after I checked it out, I found out that the original issue was the car would overheat if too long at a stop, i.e red light. But once moving would always be no more than 1/2 way up the temp gauge. He managed to drive it to work 20-30 mins away every day and avoid having it overheat.

It wasn't until 2-3 months ago that the temp started to pick up and a shop diagnosed it as a bad water pump and replaced the pump. The issue got better but still reverted back to the original situation (gets hot at a stop). They did a block test and determined it failed.

The cooling fans are not turning on which would explain why it was overheating at a stop. Either way, the shop that did the work was real ****ty and after I bought the car and on the way home, the car started to rapidly overheat at the last block away from my house. When I got home, I found that the cooling hose from the water pump broke loose because the dumbasses over at the shop did a real bad job with it and didn't even use the right hose.

At this point, I don't know the extent of what's going on so I'm pulling the spark plugs and doing a compression test on it to see where we're at.

Based on those numbers, if there are bad cylinders I'm going to further test with a leakdown test to determine where it's leaking from. But I'm hoping it's just the gasket. We'll see..

EDIT: I forgot to mention, there's no white smoke, the coolant and oil are not mixing as far as I can tell.

97rebuiltZ28

Without the fans working the LT1 engines will get hot at a stop pretty fast, especially when it’s warm outside. Was it the bad shop that diagnosed the block failing? If it was them do you know how they diagnosed it?

Injuneer

I've been active on this site for 20 years, focusing on the 4th Gen LT1’s. I can’t recall a single incident of a “cracked block”. The LT1 block is very similar to the GM “Bowtie” SBC block. I've personally seen a build that took the LT1 block to 1,125 flywheel HP, with no fill. When he decided he needed more HP, he switched to a Dart Iron Eagle Gen 1 block. The shop that built his LT1 tore it down and it was in excellent condition. Sold the block to another local, and he used it to build a 1,000+ HP nitrous motor.

We did have a “Fastest F-Body” event our local club sponsored at Englishtown back in about 2000. Serious event prize money thanks to high end sponsors like SLP. Guy with an LT1 in a 3rd Gen Camaro wanted to repeat his win from the previous year so bad he upped the spray a bit too much, and reportedly “cracked the block”. He wasn't too public with regard to the failure.

Point is, if this turns out to be a cracked block, it will be a “first”.

The head gaskets are almost like “safety valves”. The dissimilar metals - cast iron block, steel head bolts, aluminum heads - with their dissimilar rates of thermal expansion cause the problems. Aluminum expands linearly at twice the rate of steel and cast iron. Severe overheating can stretch the head bolts.

ridiqls

Yep it was them. They did a block test and it failed according to them but of course, they did the $35 block test after they charged him $1200+ for replacing the water pump.

They quoted him $3800 to do the head gasket and resurface the heads, and $4500 to replace the heads entirely.


I don't trust their work so I am doing a compression test and if it is low I will follow with a leakdown and possibly do the block test again.


Thanks, this is why I bought the car. It was a risk but given the strength of these iron blocks I highly doubt it would be cracked. I imagine the alum heads and gasket would give out long before the iron block would actually crack. And since it's not bad enough for the oil to mix with the coolant yet, I think it would be OK. But I will at least check for cracks visually and also use a straight edge to see if there's any warpage.

97rebuiltZ28

I’m by no means a skilled mechanic. In fact I don’t even consider myself a mechanic, but I have replaced my water pump twice, once with the engine out of the car, and once when I was changing the optispark and to charge $1,200 for a fairly simple 3-4 hour max job is outrageous...

ridiqls

Yeah they have really bad reviews online.


EDIT: Nm, found the ignition fuse. #11 under the hood. Fuel pump relay is near the driver's side kick panel. for anyone wondering

ridiqls

More ****ty work about said repair shop above.

I was going to make a new thread but I'll just add this here. Can someone tell me if this heater hose and valve looks right?? It does not look right to me. This is from the water pump to the valve that goes to the heater core.



This hose, broke and spilled coolant all over the road driving this car home when I bought it about 3 blocks away from my house.

And as I'm inspecting it, I have NO idea how these guys even got those 2 fittings to fit. I mean, clearly it didn't hold but that valve (left side plastic thing) is giant. The hose is 3/4" ID but has PLASTIC inside so it has no stretch to it. How they put the fitting inside the hose is beyond physics. I don't understand though how they kept it together for as long as it was (about 2 months).

Using rockauto, you can see the heater valve here: https://www.rockauto.com/en/moreinfo.php?pk=84568&cc=1035874&jsn=484&jsn=484

and the valve-to-waterpump hose here: https://www.rockauto.com/en/moreinfo.php?pk=344952&cc=1035874&jsn=782

They don't look the same as what is installed by this shop. First, the plastic valve looks nothing like the OEM part (the OEM part has a barb, this plastic valve is just a fat lip). The OEM heater hose is listed at 10" long (6"x4"). The hose on my car is about 6" long total and looks just crammed on there with couplers.


Can someone confirm this? Does the OEM heater hose have a plastic lining on the inside also? If so, how do you fit the valve barb inside of it?

Injuneer

Looks like something cobbled together. The part # showing on the valve doesn't cross-reference to any GM or AC Delco part I can find. Looks like the shop cut a length of 3/4” hose, was too large to hold the valve so they pushed something (rigid? makes no sense) into the hose in the hope that it would stay connected.

The correct valve is readily available. If the replacement hose is available, just put it back together with the correct GM/AC Delco parts. Mine's 24 years old and all still intact.

ridiqls

Gotcha, it is the worst quality of mickey mousing I've seen. The valve is actually big like 1" or bigger so it doesn't fit inside the hose. The plastic inside the hose and the plastic valve, just don't have any give it in to go over one another.

I'm thinking possibly they had another insert that went into both pieces or something that is missing on the street somewhere.

Either way I just ordered the new pieces and going to go pick it up at Oreillys.

Thanks for the help

ridiqls

Pulled all the spark plugs out of the car. #8 is a total bitch but all the other ones were OK.



No crust, no oil, they all look fairly uniform. #7 /#8 look slightly darker than #1/#2 but still looks OK.


About to do a compression test... It took me 10 minutes to get the compression tester hose into the #8 spark plug hole.


After the compression test, I would like to go back and do a leakdown test on any cylinder that's suspect. If it was any other car with easily accessible spark plugs like a honda, I would start with the leakdown for all cylinders but because there are 8 cylinders and the spark plug holes are so hard to get to, I think I'll just do it on anything suspect after the compression test.

QUESTION:
How can I find TDC on these motors?

I've watched lots of videos and never done a leakdown test (only did compression test) and just bought a leakdown tester.

Videos are showing screwdriver method, using a balloon to find the compression stroke, etc. I can use my finger or the compression gauge itself to see where the compression stroke is as it will bump the gauge a little. HOWEVER, finding actual TDC seems impossible. How do you get a screwdriver in there when there's barely any clearance??

Because the head gasket is suspect, I am willing to pull the valve covers and stuff to find TDC. Valve and head stuff I'm still new to so.. I'm reading you remove the rocker arms and you can visually see (?) the valves closed? So I can just find the compression stroke and then observe when the valves close on that cylinder after the valve cover is removed?

I'd prefer that than a screwdriver to be honest.

97rebuiltZ28

If I remember correctly, the harmonic balancer should have an arrow or dot on it and when it’s pointed straight up it’s at tdc. IIRC

ridiqls

Thanks, man that saves me so much trouble.

Found the arrow and here's a better pic of the hose situation.

97rebuiltZ28

Glad to help. Let us know how it all goes.