mannydantyla

Engine is a 4.0L straight-six with 254,000 miles on it. It's been running hot and has overheated several times. It starts to run hot after driving 30-60 minutes on the highway (depending on outside temps) and I can usually keep it under control by slowing down and turning on the heater. Entire cooling system has been replaced. I sent an oil sample to Blackston Labs to have it tested and they said there's signs of coolant in the oil.

I took the head off yesterday. The gasket looks fine, it's not blown out anywhere, none of the fire rings are cracked or have any voids in them. However, the head is warped and I can easily fit a 0.004" feeler gauge under a straight edge sitting on the gasket surface.

But what do you think?







^^ I was picking at the crud buildup in the coolant passages because I though they were blocked. But the new head gasket blocks those passages too. I guess the coolant isn't supposed to flow up from the block into the head through those passages, right?

The head is definitely warped and is going to the machine shop today:



I'm debating whether or not to pay the extra money for a valve job. Yesterday I tested the valves by flipping the head upside and pouring some acetone in the domes. All of them started to drip through the exhaust valves, about one drip every 5 seconds, except for the cylinders on either end of the engine. I tested the compression a few weeks ago and all cylinders had 140-150 psi (cold engine). The oil sample also said there was pretty high levels of lead, copper and iron in the oil which means that bearings are wearing away quickly. If the whole engine needs a rebuild soon then I don't know if I want to spend $300 on rebuilding the top end only at this time. And it might not need it anyways. Also, oil pressure is great.

The intake ports were all covered in oily dirty crud. Blow by?



But the valves and rockers where completely free of sludge:



I don't think the head has ever been taken off this engine. The previous owner kept meticulous service records and receipts, and I scoured through all of them and there was never any mention of work done on the head. There was one record though, from 2014, that said "Check for overheating. Found bad water pump, replace." So maybe it overheated real bad a couple of years ago, enough to warp the head but not damage the head gasket?

mannydantyla

Just dropped it off at the machine shop. He confirmed that it was warped. I decided to also have him take it apart, clean it, and magnaflux it to look for cracks. If non then resurface the deck and check the valves for cupping. If no problems with the valves I think I'll leave them the way they are as they're not leaking too much, save $100 that way. Or spend the $100 and get about 10 psi compression back in the middle 4 cylinders. Probably worth it in HP and MPG gains

PatHenry

The warping is enough to account for the coolant getting into the oil.

I'd have them do the valves while they're in there if they're taking it apart anyway.

mannydantyla

Yeah, I'm leaning towards that too. Why not. I can afford it I'm just a cheap *** and it's a hard habbit to break! lol

What I'm actually worried about is that this doesn't fix my overheating problem. I mean, looking at the old head gasket its definitely not super obvious that there was a giant leak anywhere but there was probably a little leakage. Kinda the same story with the oil analysis, they found some potassium and sodium, which are the coolant indicates they look for, but not a whole lot.

Maybe its just a real small leak, just enough to go undetected by tests but enough to cause the coolant temp to get too high. Real hard to detect, if not impossible, because it only leaked when engine was fully warmed up and had been on the road a while. Compression was good on all 6 cylinders (cold engine), no combustion gases in the coolant (had a local garage test it), pressure tested the cooling system and it was good. No other signs of a leaking head gasket, except for the oil test!

But there's only one way to find out and I can only do so much at a time. Worrying isn't going to do any good

PatHenry

These blocks are legendary for their durability. My dad put 400k on one and a few folks on here have hit 500k... If everything's tight and the passages are clean, you should not have a problem with overheating even with a cheapo radiator. Most folks recommend the Autozone special, so I wouldn't expect you'll need an expensive specialty radiator.

I feel like when you have the machined head and a quality gasket and take your time and correctly install the head back on that you'll be golden.

mannydantyla

Alright that makes me feel good, thanks!

Maybe while the head is at the shop I can replace some freeze plugs, check the exhaust for cracks, inspect and clean the lifters and push rods, etc.

dave1123

The oil in the intake passages is from the CCV system, therefore it's blowby. That can be stopped or greatly reduced with an oil catch can installed the the hose to the manifold. Google "oil catch can."

BlueRidgeMark

I had the same problem. No smoking gun, no obvious sign of failure. I popped a new gasket on it, buttoned it up, and drove it with zero problems until an idiot in a Suburban pulled out in front of me more than a year later.

I live out in the country so anytime I go anywhere it's 20 minutes minimum. Work is an hour to an hour and a half. I'd say replace that gasket, do the head work, and carry on.

By the way, a half dozen short-cycle oil changes (say, 2000 miles) and Rislone will clean up that gunk in your engine.

mannydantyla

That's what I'm talking about!

It seems to me that these engines can sometimes get just a tiny bit warped, enough that it can cause problems after being on the road a while but not enough to show any symptoms or be detected by any tests (at least while the engine is cold). I did everything except a leak down test: compression was great, no exhaust gases in the coolant as tested by a trusted garage, no pressure loss in the cooling system (I forgot to take the spark plugs out though), no signs of coolant mixing with oil anywhere, etc. The ONLY test that showed anything was wrong with the engine was the oil analysis. Which I never would have done if I didn't see this: https://jalopnik.com/how-a-28-labora...ine-1795355769

Here's the thing: they run great even with a warped head or blown head gasket. You'd never know until it starts to run a little hot. And when it does, you can, or at least I could, keep the temps under control by slowing down and turning on the heater. I did that well over a year, including a long trip to Colorado about a year ago. It did boil over a few times but it didn't seem to damage the engine at all.

So most people might not ever detect it. There's many folks out there, myself included for a while, who say that these engines just like to run hot and the cooling system just isn't good enough. But maybe they have a tiny head gasket leak just like you and I did, and they'll never know it!

mannydantyla

I'm having the machinist do a valve job. Said the exhaust valves were pitted and two of them were cupped. $100

Now I need to decide if I want to spend another $100 on new lifters. Seems like a no-brainer but it just keeps adding up!

I took the lifters out yesterday, inspected them and blew off any dirt that fell on them when pulling the head. They all looked good and there was no wear on the bottom where they touch the camshaft. When the engine first fires up, theres some ticking noises but it quiets down after a few minutes.

If it ain't broke, don't fix it. Right?

edit: aw screw it, another $100 isn't a lot and it will probably be worth it. A local NAPA can get all 12 of them today and they're made by Sealed Power. Is there any way to test them and ensure that they function before dropping the head on them forever?

BlueRidgeMark

Yes, and yes!


I don't know of a way to test them. I got mine at NAPA, dropped them in, and enjoyed the lack of diesel sound.

5-Speed

Just soak the lifters in oil over night. That gets them filled up. Be sure to pick up some good break in grease for the lifters if they dont come with it. I would also suggest getting a ZDDP additive to dump in the oil while you break them in. Some people will say its not good to use new lifters on an old cam but I did and it is working just fine. Breaking them in correctly is the most important part.

mannydantyla

starting a new thread.. https://www.cherokeeforum.com/f2/4-0-head-rebuild-progress-lots-question-pictures-245220/#post3497818

PatHenry

You could see if the hardware store has a replacement - they're like $7 if it's what I think that it is. However, I wasn't aware that the I6 used that type of plug, so double check the FSM/Parts manual - it could be that a P.O. stuck one of those in there instead of an actual freeze plug and that's why it's not working correctly.