MHG Leaking?

[suprajim54]

I purchased a rebuilt 7MGTE from someone locally last summer and had it installed. I was told it had HKS MHG and ARP Bolts, new stock pistons, Eagle Rods and new bearings with about 15k on the rebuild. I've put about 2500 miles on the engine and keep pushing coolant out the overflow. The cap on the bottle would pop off if I drove it really hard or for a real long time. The car runs fine except a warm up enrichment issue that comes and goes. I never see any smoke, but do smell coolant as it gets pushed out the overflow.

I tried burping it but even after an hour, the bubbles never stopped. I pressurized the cooling system to look for leaks, but didn't find any. I never had any other signs of BHG, but went ahead and did a block test. It failed after about 30 seconds of pumping the bulb. I did a compression test and I get 1:125 2:128 3:122 4:121 5:120 6:125. Low across the board, but all fairly close to each other. I tried to retorque the bolts to 90ft/lbs per ARP spec. I did compression test again 1:129 2:130 3:123 4:122 5:120 6:125, so basically no change. No leakdown tester to try to diagnose with that. So, I'm ok if I have BHG. It sucks, but I'll get it fixed myself.

I'm trying to decide now if I should just take the head off and see if there's something obvious or pull the motor and just go all in for a rebuild. I'm curious, what could cause such even, but low compression on all 6 cylinders? I expected to find 1 or 2 low cylinders, not all 6.

 

[3p141592654]

128psi is the minimum spec, so your numbers are borderline but not an outright fail,especially if you had the throttle closed during the test.

How sure are you that the gasket really is an MHG and that the block was properly prepared for one?

Your symptoms are pretty typical for a small gasket leak, that could arise from an improperly prepped block and MHG or the failure of a stock gasket.

 

[super51fan]

I bet his throttle plate was closed while doing compression test. Very few people do a proper compression test.

 

[suprarx7nut]

I would have a hard time trusting a stranger to have properly installed an MHG. It requires more than a typical partial rebuild and lots of people have been known to skip important steps.

Your figures are low, but not terrible as Pi said.

I'd start saving for a tear-down, but I wouldn't take the car offline just from the low compression test results. If it really was a reasonably blown head gasket you should find a leak with a coolant tester if tested when the block is still warm. Watch your oil/coolant and enjoy it like it is.

 

[suprajim54]

I did have the throttle open, EFI fuse pulled and all plugs out when I did the first compression test. The car had been warmed up for about 20 minutes prior to the test. When I did the second test (after the retorque), I did not have the throttle open since the valve covers were still off and throttle linkage was not connected, The engine was also cold at that point. I also did not do a wet compression test. I was shown some pictures that were supposedly taken during the rebuild from the PO, but I can't confirm it truly is a MHG. I can see the corner of the gasket near the intake side of Cylinder 1, but too hard to tell if it's metal. Even if it is, I can't guarantee that the proper prep work was done for the MHG. I'm not seeing any coolant mixing in the oil, but I do sometimes get some redddish/brown boogers in the overflow bottle. Not sure if that could be from the Water Wetter or oil in the coolant. I'd really like to fix the issue before it gets worse and I get rod knock or something.

Well, it was nice to drive the car the last 9 months, but I'll just start planning on pulling the engine and do my own rebuild. I think the only way I'll ever have peace of mind is to do it myself. And so the journey continues...

 

[Nick M]

Very few people do a proper compression test.

True. Many do more than just a compression test wrong.

 

[hvyman]

Sounds more like improper build. If it had an older design of head gasket some of the rivets need to be drilled out as they interfere with sealing.

 

[CyFi6]

You should be able to see what type of gasket was used by looking at the seam between the head and the block. The easiest place I can think of would be on the intake side of the engine right near the timing belt. You could also get in there with a mirror under the intake manifold.

 

[suprajim54]

I'm leaning toward an improper build being the cause. The guy that sold me the engine said he put 10k on the rebuild, but blew the turbo and figured it was as good a time as any to go JZ. Maybe he knew about the problem with this engine, maybe not. I haven't driven it a whole lot and have been near stock boost levels (8psi on 60-1 CT-26), but maybe I popped it. Either way, I am staying 7M and fixing this. I don't really plan on any more power than 350-400 max so that I can stay Automatic, but I want the engine to be built for 500. I'd like that cushion to hopefully make things more reliable not pushing the limits of any components. I'll pull the engine and have the block resurfaced and head checked/shaved all in preparation of a proper MHG install. I have a friend's bachelor party in Vegas in a couple weeks, so I gotta put the rebuild on hold until afterward. Maybe I'll just enjoy the car a couple more weeks and start the rebuild in May.

 

[suprarx7nut]

True. Many do more than just a compression test wrong.

I read that in a very calm and amused tone and it mad me laugh out loud. Sounds like something Ian would say.

 

[Ca104]

Check also the timing, if your timing belt is even a tooth of two off it could be why your seeing low compression. If you awe of time your valves are opening prematurely letting the compression go before your piston reaches tdc. I find it very doubtful your mhg is leaking, unless it was not installed properly.

 

[suprajim54]

As I said, the car runs fine for the most part. The compression numbers are low, but that doesn't concern me as much as the failed block test. It's a pretty simple test, so I'm confident I did everything correct. The car was warm, coolant was drained down a few inches below the radiator neck to make sure coolant didn't get in the tester and I did the test for a minute. I actually did it both while the engine was warm and cold, just for good measure. That test would indicate if there's a bad MHG, cracked head or cracked block, right? Is there anything else that could cause the test to fail? Is there anything head gasket or head related that would cause all cylinders to be equally low on compression?

I've since been able to get in touch with the engine's former owner. He says that it was an HKS MHG and should have been done correct and very hard to blow. I still have the valve covers off, so I'll double check that mechanical timing is correct.