This is an admittedly ignorant question, but I have a D1500 4x4 truck that has a body in good condition and which I generally like. The engine has been feeling "tired" for awhile, and it has 150,000 miles on it. I've looked for a replacement but I haven't found anything I think I want to replace it with, in part because I don't really want an automatic transmission, and was pondering having the engine rebuilt, if it needs to be. Influencing that is that steering was just rebuilt as were the front brakes and a front axle u-joint.

I'm getting really mixed signals on whether the engine should be rebuilt or not. One cylinder has 70lbs of compression and I know that it should be something like 120. The mechanics shops where it has gone to always seem to be vague on the topic and to sort of suggest that its just easier to get a new truck.

So how does a person really know when to have an engine rebuilt prior to it just completely failing?

 

You can replace it with any engine as long as you use the pressure plate from your engine. Also its just called a 1500 in those years . Welcome!

 

I'd be tempted to replace the engine with a little bigger displacement one, if it actually needs to be replaced or rebuilt.

That's my problem, I guess. The shops all seem to assume that at 150,000 miles you aren't going to really hang on for it for more than a couple of years, so it's good enough as is. So knowing when you really need to rebuild or replace is hard to determine, unless I suppose you are a real mechanic and I'm not more than an amateur shade tree mechanic at best.

 

If you have a cylinder down to 70 psi, it is time for a rebuild/replacement, if you are planning on keeping it, which it sounds like you are since you already have some money in repairs. I believe the general consensus for lowest acceptable compression is a minimum of 100, some say 120. I pulled one out to rebuild and I had two cylinders down, one at 70, other at 80. Personally, I would do a rebuild, but not sure of your mechanical skills or what kind of money you have to invest. Crate motors are out there, someone may be able to comment on experience with those, or if you have a good mechanic that could rebuild yours. Getting a used motor is a crap shoot, may get a good one, may not. Keep us updated...
Not sure what motor you have, 5.2 or 5.9, or otherwise, but if you have a 5.2 you could upgrade to a 5.9 with little additional parts needed.

Keep us updated...

 

At 150,000 miles, I'll bet the timing chain is worn out. You might be surprised at how much a new timing set will wake up an engine as well as really put the heat out come winter. One cylinder low is concerning but I'm wondering if two tests were done or just one. Before I replace an engine, I do at least 3 compression tests. One cold, one warm and let it sit overnight and another cold. If a cylinder is consistently low, somethings wrong. If it only shows on one test, maybe the tester wasn't seated properly.

You like the truck, the chassis has had a lot of work and I'll bet it's paid off. With it idling, listen to the front of the engine. I'll bet you hear some timing chain rattle. Chrysler came out with an updated timing tensioner in 1998 or '99. It'll sound sort of like "Shika,shika, shika".A timing chain will be about the same as one or two truck payments.

 

Low compression doesn't mean you need a complete rebuild. Could be a bent valve, Bad head/gasket. A refresh might be the way to go with out a complete rebuild.

 

Do another compression test. Dry first, then add a tablespoon of oil to each cylinder, and see what the numbers do. If they jump quite a bit, then your rings are shot, and it's time for a rebuild. If they don't change much at all, then it may just be time to put some better heads on it, and you'll be good for another 100K miles. If you have an air compressor, doing a leak down test will tell you exactly where your compression is going. (you'll be able to hear it.....)

What size engine do you have in there now?

 

As a follow up, after everything was said and done, we took it elsewhere and after the new shop looked at it, they ended up taking off the air intake manifold and found a seal was a complete wreck. That was replaced and now the engine is performing like it should.

 

Doing the timing chain will help as well.

 

Thanks.

The next set of Dodge work projects might be on my 07 D3500 4x4. Need four new tires and trying to decide if I should try to go up to 35" tire sand if that will require some sort of lift. And if that's even a good idea.