LS400FAN

Well guys I didn't want to face reality but the time has come to replace the hg on my 95 LS who I've always glowingly referred to as the THE BEAST, I truthfully never thought it would fail me like this, but it is what it is. The saddest part of this story is I just had it hit with a fresh coat of paint, go figure. Here's the deal, the signs of a blown hg is is unmistakable. CEL codes of 300, 306 and 308 never go away and I'm burning coolant like crazy. I will do a compression check tomorrow to confirm but I'm willing to bet my right arm that it will be confirmed. I've replaced hg's on a number on cars but never on the LS, I would be grateful for any tips, suggestions or helpful comments from anyone who's done this job before I get started. It looks to be pretty straightforward and I don't anticipate much of a problem but willing to accept any info that anyone wants to share. I wasn't really looking to spending the rest of my summer dealing with this, but at 275k miles it has to be done. I only hope its just the hg and not a cracked head or block, and to think I've always thought this engine was bullet proof. Like I said, any info anyone wants to share will be much appreciated. Thanks in advance.

Cheers.

timmy0tool

iTrader: (7)

all my years in CL i have never seen an actual HG failure on the 1UZ...so you might be the first if it truly is one. before your rule it's a HG, check the following:
did you run the overheated engine for a long period of time?
any other cracks in the cooling system? radiator and hoses are first checks.

a compression check would tell you a lot. i haven't heard of coolant burning unless something else is compromised (but again the HG isn't my first pick).

i've ran my engine in the hot for a minute after noticing the needle pegged in H, then blasted the heater and rev'd the engine to get the coolant moving which brought the temps back down. come to find out i had air in the system and after burping, the problem went away! i'm sure a long duration in an overheating condition will result in many other problems.

YODAONE

The coolant is going somewhere:
Either a hose or gasket leak, into the oil or exhaust.

Have you inspected spark plugs?

New OEM coolant reservoir cap?
Water pump is not leaking?
Water control valve on firewall is not leaking?
Thermostat ever replaced? OEM?
Block Draincocks fully closed?
Radiator ever replaced?

LS400FAN

Hey Tim,
thanks for your input, I guess I should have given more info in my post. The coolant is "clearly" coming out of the tail pipes in very noticeable plumes of smoke(vapor),and the smell is most definitely coolant. It's not burning any oil from what I can tell. No oil in the coolant expansion tank and no coolant visible in the oil. My guess is the hg is compromised between the #6 and #8 cyls, since these codes are the only ones showing up. I pulled the spark plugs and they all looked normal, the #6 plug was a little damp but still looked pretty clean. By the way, I've replaced all of the plugs and still the same result. The eng would run smoothly after start-up until operating temp and idles down, btw normal idle has always been at 600 rpm on this puppy, I know it should be around 800-850 rpm but it never caused any problems so I left it alone. But to answer your primary question, coolant is most definitely being burned and coming out of the tailpipe, no leaks anywhere else. The eng never overheated and I've owned it for 14 yrs. The compression test is next, I'll keep you posted. Thanks again.

LS400FAN

Yep Yoda, I've ruled out all of those symptoms, btw I forgot to mention I do get the flashing trac light, so it's definitely malfunctions in those two cyls. Hopefully, the compression check will tell me what I need to know, I just hope its not a "cracked" head or block(however if that was the case I would most likely be burning oil as well), a blown hg is a piece of cake comparatively. I honestly can not think of any other reason why I'm burning coolant other than the hg, "especially" when it involves two adjacent cyls, can you? Thanks for chiming in.

LeX2K

Pressurize the cylinders see if air leaks into the radiator. This is the most reliable way to know for sure if you have a blown HG.

LS400FAN

Will do 2K, thanks.

LeX2K

Naturally the valves need to be closed on a given cylinder when doing this. You'll know, air might blow out the intake or exhaust. If the piston is not at the bottom of the stroke the engine will rotate suddenly so keep that in mind if you have a wrench or ratchet on the crank bolt.

LS400FAN

Well here's the latest, the cyl #6 and cyl #8 are testing a very strong compression of 205 and 220 respectively, there's no way the hg is compromised reaching those kinds of numbers and holding. This is a real mystery to me, if it's spark related or injector related then why is it burning coolant which is noticeably fogging up and blowing out the tailpipes?? Someone suggested that it could be leaking thru the intake manifold, but how could that be? From my knowledge where could coolant be flowing thru the intake manifold? Or is there? To my knowledge only fuel and air flows thru the intake manifold, please correct me if I'm wrong. Thanks, I'm still scratching my head on this one.

bradland

When do you notice this? Constantly whenever the car is running? Only at start up...?
I don't remember if the throttle body on a 95 has coolant flowing through it or not...

Yamae

I'd try this for the precise confirmation.

LS400FAN

Thanks Yamae, not only am I going to do this, I'm also going to do the leak down test as well, I'll be buying those items tomorrow. I'm curious with your experience have you seen many blown hg's on the LS engines? Thanks again.

Cheers.

LS400FAN

Hey Brad,
it started out a few weeks ago as intermittent after the engine warmed up, but it's gotten progressively worse and now does it on startup. I just realized my compression test is not complete because I only tested the 2 adjacent cyls (6&8) which is where the problem is, I will do another cyl for comparison. 6 & 8 are most likely just feeding off of each other, I've never seen 200-plus readings on compression checks on "any" vehicle.

aptoslexus

Well, there is a coolant pipe under the intake manifold. It's very close to the intake ports of the back two cylinders, so if the gasket there has sprung a leak, it's possible there's coolant entering the intake there. It's a metal gasket, so a failure is unlikely, but I guess it's possible.

LS400FAN

Good point apto, however its a longshot because two things would have to happen in order for that to occur. 1st, there would have to be a leak from the coolant pipe/hose underneath the intake manifold, and 2nd, the intake manifold gasket would have to be breached, none of those things has happened because I can easily see if the coolant is leaking out of the pipe/hose and its in tack, plus coolant would be present in the valley under the intake which it is not. Thanks for the suggestion.

Cheers.