91Pioneer Posted January 15, 2016 Share Posted January 15, 2016 Background: Truck was really neglected before I bought it. Like big time. I installed the full gauge cluster out of a 93/94 XJ and used the sensors right from that vehicle. Here's the deal, when the engine is fully warmed up the gauge is dead on accurate, goes down to 1/4 mark or so at idle in gear, goes up almost pegged if I'm driving fast on the highway against the wind. Driving normal at highway speed puts it between 1/2 and 3/4 ish. The only thing is after a startup while the engine is cold and warming up, the thing will go right off the scale past high, like pegged out. But not necessarily when the engine is revving. Like it could read normal with RPMs up and when you let off it can spike beyond max. The fact that everything is perfect when the engine is warm makes me think the sender is good. I don't want to drop $ to buy a new sender if it's not the problem. But at the same time the truck was driven for 20+ years with no gauge and runs great. My only other suspicion is that there is junk / gunk bits of thick oil crap inside the engine. I plan on changing the oil again soon 'cause it's super dark. I have been thinking of doing an engine flush prior to draining the oil. I haven't done a flush before but I figure it won't hurt anything here. I have a couple of quarts of ATF so I'm debating of using that for a week or just using a 10 minute flush. Thoughts? Link to comment Share on other sites More sharing options...
Eagle Posted January 15, 2016 Share Posted January 15, 2016 What weight oil is in the engine, and how cold does it get at night where you live? It might be helpful if you give us the actual numbers instead of reading the oil pressure like a gas gauge. Link to comment Share on other sites More sharing options...
91Pioneer Posted January 15, 2016 Author Share Posted January 15, 2016 5w30 but it did that in summer too. It reads in bar (metric) so you probably don't want the readings LOL I checked the owners manual to make sure the engine oil pressure is OK when warm which it is. Link to comment Share on other sites More sharing options...
gogmorgo Posted January 15, 2016 Share Posted January 15, 2016 Took me forever to figure out what the hell the numbers were on my oil pressure gauge. It goes from zero to 5.4, and the halfway mark is 2.3 if memory serves. Those numbers are meaningless to me, even knowing they're in bar, so I stopped paying attention to them. Needle pointing straight up while driving is good, needle ever pointing at less than quarter is bad. I think that's based on a conversion I did to psi and what pressures should be according to one of Eagle's posts from around the time I joined CC. Link to comment Share on other sites More sharing options...
Eagle Posted January 15, 2016 Share Posted January 15, 2016 I expected that the Canadian gauge would be in kPa -- that's what the FSM uses. Numbers are numbers, they are more precise than "halfway." That said, if max is 5.4 then straight up (the mid-point) should be 2.7. The U.S. gauge has a range of 0 to 80 psi, and the mid-point is 40. The quarter point is 20 and 3/4 is 60, with tick marks at the tens. The scale is linear, not exponential. The FSM spec for oil pressure (for the 4.0L) is 13 psi (89.6 kPa) minimum (warm) at idle RPM, and 37 to 75 psi (255 to 517 kPa) above 1600 RPM. 80 psi is 552 kPa. 75 psi is 517 kPa, so the FSM is just doing a direct conversion. 40 psi is 276 kPa. To convert kPa to bars, just divide by 100. Link to comment Share on other sites More sharing options...
gogmorgo Posted January 15, 2016 Share Posted January 15, 2016 Okay, it's just a 3. My recall was aided by this photo, And I ASSumed there was a digit hiding behind the needle (2.3 seemed more likely than 3.3), but it's just a three. Ran out and confirmed. For reference, that photo was taken at idle. My best guess for them using bar is so they aren't cramming digits onto the gauge. Link to comment Share on other sites More sharing options...
Eagle Posted January 15, 2016 Share Posted January 15, 2016 Okay, it's just a 3. My recall was aided by this photo, And I ASSumed there was a digit hiding behind the needle (2.3 seemed more likely than 3.3), but it's just a three. Ran out and confirmed. For reference, that photo was taken at idle. My best guess for them using bar is so they aren't cramming digits onto the gauge. Morons. If they were going to round off 2.7 to 3, why not round off 5.4 to 5 ... or 6? It's not like those gauges are finely calibrated, precision instruments. Link to comment Share on other sites More sharing options...
gogmorgo Posted January 16, 2016 Share Posted January 16, 2016 :dunno: Don't blame the Canadians for that one. The metric-speaking countries outside of North America are a much larger market than humble Canada. At the time, most Canadian-spec cars from US manufacturers had oil pressure gauges in kPa, and also speedometers that only went to 140km/hr, which is a hair over 85mph. The rest of the metric-speaking world enjoyed gauges that somewhat reflected a vehicle's top speed, and used bar for just about everything automotive. The French have always been a bit laissez-faire with their numbers. I blame Renault, and cite my speedometer that goes to 120mph and the ridiculous oil pressure gauge as evidence. But we're getting kinda off topic. My parents neglected their old Chevy van pretty badly, like possibly 50,000+km and 5+ years between oil changes. (i was too young to know better). By the time I was old enough to be driving it frequently, the pressure gauge on it (in kPa) would pin itself to the top the way 91pioneer describes, and generally be kinda high. That beast kept trucking until it was almost 30 years old with an estimated 450,000km on it (the odometer quit working somewhere around 350k) when the timing chain skipped and a mechanic finally convinced my parents to get rid of it. Sure, it burnt and/or oozed a crap ton of oil, but beyond that I don't think the increased pressure really did much harm to it. As far as actual solutions to the problem, I seem to remember mentioning it to a mechanically-inclined individual or two, and blow-by and crankcase ventilation come to mind as possible causes, but we're talking over eight years ago now. Link to comment Share on other sites More sharing options...
NorthWoods Posted January 16, 2016 Share Posted January 16, 2016 I'm gonna say that crankcase ventilation is a strong possibility in the symptoms you are showing. You seem to be building a ton of pressure until you warm up and whatever clog you have is giving way and allowing the pressure to work its way down. Link to comment Share on other sites More sharing options...
Rockfrog Posted January 16, 2016 Share Posted January 16, 2016 Okay, it's just a 3. My recall was aided by this photo, And I ASSumed there was a digit hiding behind the needle (2.3 seemed more likely than 3.3), but it's just a three. Ran out and confirmed. For reference, that photo was taken at idle. My best guess for them using bar is so they aren't cramming digits onto the gauge. I solved that issue by swapping in a set of US guages for the oil pressure and the engine temp. Now I can make sense of them now, I didn't grow up completely metric (that was an interesting school year to say the least). Also added a mech oil pressure guage a while back as paranoia set in. Between the exhaust leaks and the piston(s) slap ... I tend to over worry about the old ticker (88 4.0L). But she just keeps moving along. Link to comment Share on other sites More sharing options...
gogmorgo Posted January 17, 2016 Share Posted January 17, 2016 Now there's an idea. Putting it on the list of things to maybe think about doing eventually. Link to comment Share on other sites More sharing options...
91Pioneer Posted January 27, 2016 Author Share Posted January 27, 2016 Well I found a good source for MMO in Canada so I bought some. I'm going to go ahead and change the disgusting oil soon and put in a quart of MMO in place of oil and give it some time. The truck was severely neglected before I bought it so hopefully MMO will clean 'er up internally. Maybe that will help with the oil pressure readout. Maybe not but it's something I've kinda been wanting to try anyway. Link to comment Share on other sites More sharing options...
Crash Posted January 28, 2016 Share Posted January 28, 2016 Definitely put a mechanical gauge on to confirm your pressure. Some of the kits have a long enough hose to run up to the cowl so you can confirm while driving. Link to comment Share on other sites More sharing options...
gogmorgo Posted January 28, 2016 Share Posted January 28, 2016 Outta curiosity, what is this good source? Hope it works out for you. Link to comment Share on other sites More sharing options...
91Pioneer Posted January 28, 2016 Author Share Posted January 28, 2016 Costco just added it to their site, box of 6. I've never seen it locally. The way Costco works it might be off their site next month forever. My gauge reads a bit lower than yours, hot idling. I tend to look at my gauge straight on when I read it and your off to the left for obvious reasons. Link to comment Share on other sites More sharing options...
91Pioneer Posted January 28, 2016 Author Share Posted January 28, 2016 Definitely put a mechanical gauge on to confirm your pressure.I'm thinking about that, I might. Link to comment Share on other sites More sharing options...
gogmorgo Posted January 28, 2016 Share Posted January 28, 2016 The motor in question only had around 245,000 km, don't know what yours has but if it's been neglected it likely has a bit more bearing wear. Beyond having the crap beat out of it as a plow truck, the XJ I pulled it from seemed to have been reasonably well looked after. Also, I was running 10w40 at the time, if you're on 5w30 it's bound to be a bit lower. I'm not a costco member... I went with my roommate a whole bunch a few years back and was going to get my own membership after he moved out, but then they quit carrying the awesome mini pizzas, so I said screw it and haven't been back. Lol. Link to comment Share on other sites More sharing options...
Rockfrog Posted January 28, 2016 Share Posted January 28, 2016 I can find it (MMO) at Can Tire and Walmart around my neck of the woods. Link to comment Share on other sites More sharing options...
91Pioneer Posted January 28, 2016 Author Share Posted January 28, 2016 Neither store carries it here. I'm sure I did see it at one of them like 10 yrs ago. Link to comment Share on other sites More sharing options...
91Pioneer Posted March 5, 2016 Author Share Posted March 5, 2016 Well I thought I should post an update. It turns out the sender was bad. The spring inside was not working so when pressure went up the spring did not properly move the little plunger back out which drops the pressure reading. I just replaced it with a junkyard one and it's working wonderfully now (I was too cheap to spend $45 on a brand new unit LOL), I don't have an actual oil pressure problem which is great :thumbsup: Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now