D1 Oil Pressure Light on idle and heavy leaking

**NOT FIXED - See my comment below**

I just picked up a 1998 D1 ($850) today and drove it about 140 miles without much issue. The first sign of an issue was when we slowed for an accident on the freeway and the oil pressure light came on. I pulled off at the next exit and topped the oil off (the seller left me with some - knowing there was a significant leak that was disclosed). Drove over a mountain range and was watching the temp gauge very closely. It rose to about the 3/4 level when climbing up the mountain at 70 mph, but then dropped without issue when it leveled out or on decline. Stopped for some more oil along the way and again noticed the oil pressure light when coming to a stop. Checked the oil level and it looked fine. Looked under the car and it was leaking pretty good...but you know these things carry a lot of oil. Anyway, continued on the trip and made it to the emissions inspection station. Once off the freeway, my revs were lower and again the oil pressure light was on. By the time I was done with the inspection, the temp gauge was up at about 3/4 again. I drove out of the station and parked it as soon as I could...before it exceeded the high temp mark. I could see steam from the hood (not a ton, but noticeable). And...there it sits right now after getting an Uber ride a few miles home.

I'm a newbie at working on cars, but I'd love to try to sort this out myself...with some guidance. From what I've read, the first step seems to be to test the oil pressure...but I would think that would only verify what seems to be part of the issue. Low oil pressure leading to temp issue...but it was fine going 70 mph for 2.5 hours including incline.

Thoughts? Advice?

Thanks in advance!

-G

Thanks for the response! I have an update on what may be at least contributing to the coolant temp issue. When I turned on the air conditioning, the temp rose right away. When I turned it off it dropped. The temp did rise a bit without the air conditioning on but turning the heat on helped drop the temp.

I have an ODB2 Bluetooth device and it seems that the what the gauge is reading as the normal temp ends up being around 200?. And got above 220? without AC. I haven't had it plugged in when the temp gauge is elevated yet.

Another 98 Disco that we have was closer to 180?.

UPDATE:

I was able to fix both issues this weekend (with the help of a friend that knows a lot more than me about these trucks).

The oil leak was actually coming from the oil pressure sender. I went to the DIY car wash and washed the heck out of that passenger side of the engine underneath. Used brake cleaner and scrubbed. Once the area was all clean, it was clear that the oil was spewing out of the oil pressure sender. It's a 1/2" 20 UNF and were able to plug it until the replacement part arrives. I haven't driven it enough to know if there is another leak, but this was a massive one and it's fixed. No other signs of other significant leaking.

The overheating was caused by a bad fan clutch. It must have been slipping too much and not able to keep the RPMs needed to keep the coolant cool. I also flushed the coolant and replaced with the green stuff/water mix.

The oil pressure sender is $6 and the fan clutch was about $50. So now I just need a new set of tires and it'll be ready for daily use.

Thanks all for the insight and tips. Very helpful and appreciated!

-G

So it seems I claimed victory too soon. The coolant temp is still getting up over 230 f. I'm going do the thermostat, water pump and hoses next. Did a compression test and all cylinders have similar compression. I also did the sniff test on the coolant and the fluid didn't change color...so it doesn't appear to be an issue with the exhaust in the coolant. There are still some metallic flakes in the coolant after I flushed it and I'm not sure if it's due some leftover stop leak stuff or if it's from something else (like the water pump failing or rust from the radiator). I'm holding off on the radiator until I do the less expensive stuff to see if that fixes it.

I'm open to thoughts on this as well...and I'll update once I get the thermostat, water pump and hoses changed out.

-G

p m said:

Use IR gun on the radiator - it should tell you if part of it is clogged. Normally, there's about 15F temperature drop across the radiator, side-to-side, and there should be very little variation top to bottom.

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Side to side at the top? Top to bottom on a particular side? Isn't it supposed to be cooler coming out than going in?

Friend has a Disco 1 that holds well at about 195 f. I took some temp readings last night with the gun and here's what I got after they both warmed up.

Radiator in (metal):
Mine - 205
Other- 175
Lower rad hose:
Mine - 145
Other- 115
Water pump:
Mine - 162
Other - 128

edthediscoman said:

I would replace the T sat, sounds like its not letting the hot stuff out fast enough. Or remove it.

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Well, I tested the top in on the radiator and it was cool until the coolant hit about 205 (according to ODBII device), then the thermometer opened up and seemed to act as expected...but you may be right. There may be some flow restriction there. I'm going to replace it either way.

The other strange thing is that the coolant level has been dropping. To be honest, when I bought the truck, I drove it the 140 miles home and not much more than that. But the coolant level didn't seem low at all. I've driven much less than that and it had clearly lost a significant amount of coolant. I just flushed the system.

Anyway, I have a new rad cap and washer and will use the overflow tank cap from the other truck just to eliminate those as the culprit. I'll also have to check the oil for coolant. All sorts of fun here.

p m said:

Assuming it was "thermostat" that opened up - if it opens so late, it almost universally means that you have a giant air pocket in cooling system. I'd replace thermostat with any generic one, but drill a 1/8" hole in the flange in 12 o'clock position so thermostat does allow some flow even when it is closed. OEM thermostats had "jiggle pins" for this purpose - not all off-the-shelf thermostats have it.

Overflow tank cap is most definitely not a cause of overheating.

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I already have a replacement OEM one from Atlantic British that has the jiggle pin. So hopefully that helps. Also, the tank cap wasn't really an overheating concern more of just another issue. And trying to determine where the coolant is going .

Thanks for the reply.