pm59723

Hey all,

Long time reader, first time poster. I picked up a new-to-me 89 5.0 2wd manual a few months back. At the time, the previous owner mentioned that he would get seemingly random "Engine" light pops, and had done some digging but hadn't found a solution. I've been combing through posts and doing a few things here and there, but now I'm stuck too, so I thought I'd throw it out to y'all to see if anyone could point me in the right direction.

So to be clear, the light I'm getting is the redundant red engine light, not the yellow check engine light. I've read a few posts on this forum suggesting the "engine" light is a light that specifically pertains to gauges, not the computer system.

Here's what the owner's manual says: "In addition to the temperature gauge and oil pressure gauge described above, vehicles with RPO tachometer instrument cluster are equipped with a redundant ENGINE warning light which is calibrated for maximum safe engine operating temperature and minimum safe engine operating oil pressure. If the warning lamp lights while the engine is running, the engine must be shut down as soon as possible and gauges checked for either low oil pressure or high engine temperature."

So here are the details:

OBSERVATIONS: I get either blinking or solid "Engine" lights in two scenarios: 1) When I've almost stalled, seeming to be a result of a low idle; 2) When I've traveled at highway speed (55mph+) for more than 10 miles or so and return to an idle.

WHAT I'VE DONE: The first thing I did was read the owner's manual, haynes and this forum. After that I came up with a few guesses to track down. First, my oil pressure gauge is inoperable. It's not even working in dummy mode, it's just broken. As a result I took my truck in for a mechanical oil pressure test, which came back ok. According to my mechanic it tests between 13-15 PSI per 1,000 RPMs.

I've also kept a close eye on my coolant level. It lost some coolant a few weeks back, because the radiator cap wasn't screwed back on all the way, and since then It's been a little low on and off, but not visibly leaking. The problem preceded this event. My thought is it needs to be burped, but I haven't gotten around to that yet. I don't take it out on the highway much so it doesn't really get too hot. When I do drive for more than 15 miles at highway speed it does run a little warm when back at idle (fine while at speed) - roughly between M and A on NORMAL (regular around-town gauge level is between O-R). Fan clutch is good, doesn't free-spin when system is cold.

I bought a code reader on amazon, and checked for codes twice. Both KOEO and KOER came back with nothing but all-clear codes (after I realized I had missed a step and inadvertently got a 52 code because I didn't engage the power steering pump the first time around).

QUESTIONS: So where do I turn from here? Is is possible that the light is being tripped because the oil pressure gauge is inoperable? Any other ideas?

88xlt

I've got a darned good idea of the whole thing. From what you describe from the engine being warmed up good and then the engine light coming on at slow engine speeds, you probably do actually have low oil pressure. You will probably get along well with that engine for a long long time if you just don't let the engine run for any length of time with the engine light on. This seems to happen quite a bit with 5.0 engines. It might help to use a little thicker oil.

How many miles on your truck?

pm59723

146k. Given that the pressure check came back ok before, and he had it hooked up for 45 min, but admittedly didn't see the warning light, I guess I'm just curious what could be causing the system to trip. Is there a chance it's an instrumentation issue only? An inoperable gauge might suggest an inoperable oil pressure sending unit or some other electrical issue, right?

Obviously I'm hoping it's not something major like bearing clearances.

What do you mean by any length of time? I've got 10w30 in it now.

88xlt

What do I mean by any length of time. Ideally no more than say 30 seconds. Don't let it sit in your yard and idle with the engine light on or if in a traffic jam speed up the engine enough for the light to go off.

Yes it could be faulty instrumentation. If it is actually low oil pressure, it's probably caused by worn bearings. Even if it is worn bearings and you treat it right it will probably last a long time.

The inoperable gauge is probably the gauge itself.

pm59723

Ok thanks! Wasn't sure if you were being literal there. "Any length of time" can be used as a flexible phrase here in the southeast

So next steps in your opinion to both diagnose and treat it right?

I'm guessing here: change for higher viscosity oil. We don't get below freezing much here, but occasionally have a week or so below freezing. What should I step it up to? Will having more viscous oil help much?

How can I go about testing the instrumentation? Anyone have links or other reading materials to suggest? Should I run another pressure test and try to replicate the issue in the shop? I'm guessing that's the quickest way to determine if I'm actually bottoming out on pressure or not.

There aren't any signs of failure in the way of noises, but again, I know this is a crapshoot. Anything else I should be looking for as a way of figuring out what's going on, or other advice besides not going on the highway in the near future?

88xlt

You don't need to stay off the highway, just don't let it idle too long with the engine light on. You could probably warm it up to where the engine light comes on and have the test done with the gauge to know for sure where you're at.

I would probably use something like 15W40 Rotella. I think that all says it's for diesel engines but that's OK to use.

They say the engine light comes on when the oil pressure drops below about 7PSI so you may still have some pressure at idle.

Again it could be faulty instrumentation, but just from what you describe it acts like to bring the light on it acts like low oil pressure. Again if you treat it right it may run a long long time.

pm59723

Just an update. Changed the oil out for 20w50. So far all signs point to engine wear. ENGINE light no longer flickers or comes on after traveling at speed and returning to idle. Only time I've seen it since was when the engine was up at temp and then I engaged the power steering almost full stop.

I'll probably swap out for 15w40 once we get closer to winter to help cold starts.

Thanks for the help!