1990 Buick Lesabre

 
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carlherrnstein
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Post by carlherrnstein » Tue. Mar. 16, 2021 11:31 pm

I have acquired a 1990 Buick LeSabre it has 102k miles on it currently. I
Being a 30 year old car it has a few issues.

Biggest concern is when the engine is up to temp the oil pressure light will flash on and back off when it's shifted into gear. It only does this when it's warm. I figured it was a bad switch, I replaced switch but it still does this. I have yet to hook up a mechanical gauge to get a actual pressure reading however it does not have a lifter tick. I changed the oil when I got it 10w30 conventional. I'm wondering if there is a screen to keep junk out of the switch that could be plugged. Does anyone have any suggestions?

Second issue is "mud" in the cooling system. It had no heat I flushed the heater core/engine/radiator with water. Holy crap the coolant was orangeish brown. I thought it was rust/hard water at first but, I remember GM used a special coolant that turned to mud after a few years. What will clean that crap out without killing the heater core/radiator? Water pump bearings are loose but the seals are good for now and a new pump is on order so if it wipes out the pump so be it.


 
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Post by KLook » Wed. Mar. 17, 2021 6:33 am

There was a product the local mechanics used to flush, can't remember the name but it will be available in any parts store. The risk of creating a leak is certainly there if it is that badly gunked. It has had a lot of time to corrode. Run some seafoam or marvel mystery oil thru the fuel system. Techron works also.

Kevin

 
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Post by warminmn » Wed. Mar. 17, 2021 8:44 am

Its possible it does have low oil pressure as between gears it would be at about its lowest. A mechanical gauge would be the quickest way to find out. Hopefully its just a blockage somewhere. Those were real good cars and usually they would just be getting broke in at 102K miles. But if the previous owner didnt maintain it, it could be worn out too. I'd plan on changing the tranny oil too unless theres a sticker somewhere saying it was recently done.

 
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Post by coaledsweat » Wed. Mar. 17, 2021 9:05 am

That mud thing is probably someone added Dexcool to regular anti freeze. Man is it a nasty mix! Anyway, a good clean and flush should cure it.

 
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Post by D-frost » Wed. Mar. 17, 2021 10:53 am

Carl,
If the lifters are quiet, it could be 'electrical'. If it has the V-6, I think the sending unit is near the oil filter. The wiring probably runs up to a relay pack under the hood. When you put it in gear, the shift linkage from the steering column maybe wiggling the wire harness. My father-in-law had one of these....nice car, good gas mileage(18-24 mpg) with the V-6.
Cheers

 
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Post by Rob R. » Wed. Mar. 17, 2021 11:33 am

I believe those engines were notorious for coolant leaks at the intake manifold. The crud you are seeing might be stop leak.

 
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Post by StokerDon » Wed. Mar. 17, 2021 12:32 pm

In automotive engines oil pressure is determined by the main bearing clearance. If the oil is at operating temp and the pressure is low, the mains are worn out. In my experience, no amount of magic flushing or cleaning will fix that. Sending units normally work or they don't so that's not a likely problem but you might get lucky.

The first step to check this would be what Warm suggested. Put a mechanical pressure gauge on it to find out what the actual oil pressure is. The cooling system problems could have caused this. Running the engine hot will kill the oil and lead to internal engine ware.

Good Luck!
-Don


 
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Post by Richard S. » Wed. Mar. 17, 2021 12:45 pm

carlherrnstein wrote:
Tue. Mar. 16, 2021 11:31 pm

Second issue is "mud" in the cooling system. It had no heat I flushed the heater core/engine/radiator with water. Holy crap the coolant was orangeish brown. I thought it was rust/hard water at first but, I remember GM used a special coolant that turned to mud after a few years. What will clean that crap out without killing the heater core/radiator? Water pump bearings are loose but the seals are good for now and a new pump is on order so if it wipes out the pump so be it.
I had one that had a lot of sludge in the coolant, 3800 in a Regal. AFAIK it was caused by intake gasket which is common problem on those cars. The oil would get into the coolant but not vice versa. I'd just flush it occasionally. The permanent fix is not terribly expensive or hard, especially if you can do it yourself. Keep in mind the 3800 engine in that vehicle is known for longevity, 200K plus is common.

The coolant itself is also possible culprit if the types were mixed, look up coolant silicate drop out. The coolant type is not necessarily an issue but you can't mix the new coolant with old coolant.

If you start working on the pump consider replacing the coolant elbows. From what I have read it's also a pretty common for these to go bad, I know one of mine failed and if it does you pretty are much stuck wherever it fails. It's very simple fix and they only cost a few bucks, it may save you from being stuck on the side of the road somewhere.

Coolant elbows on GM 3800

 
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Post by Richard S. » Wed. Mar. 17, 2021 12:54 pm

D-frost wrote:
Wed. Mar. 17, 2021 10:53 am
My father-in-law had one of these....nice car, good gas mileage(18-24 mpg) with the V-6.
18 if you are driving on very busy side streets. 22 to 24 where it's not so stop and go. 28 to 29 going 85mph on a highway with varying elevations. When I was in Indiana for the meet and greet at Hitzer it was telling me 33 on perfectly flat highway but I think I was only going about 65ish with cruise set.

 
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Post by fig » Thu. Mar. 18, 2021 11:22 am

I think there was a recall on the coolant intake manifolds on the v6. Regardless it should be upgraded. It can leak coolant into the cylinders and cause the engine to hydro lock.

 
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Post by warminmn » Thu. Mar. 18, 2021 12:12 pm

Intake manifolds always seemed to leak in the 1990's. Some were plastic type manifolds and it often didnt work. Maybe some were ok. But instead of realizing they should give up and go back to cast they kept doing it anyway. GM 3.1, 3.8, Ford 4.6, others. Its a long list. Some had recalls and some didnt. I am unsure if all of them were plastic but it seemed to be a universal problem at that time with intakes. I have no idea if it improved since then as Ive never had one. The 3 engines i mentioned were all solid engines but had that failure point. Fords 4.9 was the water pump. They all have a weak spot I guess.

 
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Post by hank2 » Fri. Mar. 19, 2021 1:03 am

GM didn't start using dexcool or plastic intakes until '95. The 3800 was completely redesigned about the same time. Block, bottom end, cylinder heads, etc. The mud and orange could be from someone adding dexcool to the conventional coolant, which would be a big no-no as Richard mentioned. Or, it was never changed and topped off with tap water and there's a lot of rust. And/or added Gm stop leak tablets. If the coolant was neglected that badly the PO's may have also been care free on regular oil changes, etc. Hopefully a total cooling system flush will get you back on track and the oil pressure problem is fixable.

I ran a '92 LeSabre for a couple of years. No real engine problems, other than a cracked coolant elbow, but always trouble with the Transmission module and charging system. I sometimes had to access the module under the dash and gave it a strategic slap on the side. It liked to start out in 2nd gear and stay there. 22 mpg local and about 27 mpg hwy.

 
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Post by Richard S. » Fri. Mar. 19, 2021 5:22 am

hank2 wrote:
Fri. Mar. 19, 2021 1:03 am
22 mpg local and about 27 mpg hwy.
I should note my mileage estimates from above are from series III 3800 which has a little better efficiency and HP.

 
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Post by warminmn » Fri. Mar. 19, 2021 9:14 am

Just in case you need something significant, I've used this site to find used parts for years. You can search by distance also. Stuff I look for is older so sometimes I have to travel a distance but at least you dont have to be on the phone all day looking. Make sure to have the dash between car and part or its a different site. https://www.car-part.com/

 
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Post by fig » Fri. Mar. 19, 2021 12:53 pm

Richard S. wrote:
Fri. Mar. 19, 2021 5:22 am
I should note my mileage estimates from above are from series III 3800 which has a little better efficiency and HP.
I’m currently driving a 05 Buick Lucerne CSX and get those mpg’s with it. It’s a V8 with 285 hp I believe. I was driving a 2000 Park Avenue before the tranny but the dust. Got around the same with it. The Lucerne has tons more power. Drives like a truck though with those 20” rims. That was a big disappointment. I was expecting Park Avenue ride. Buick’s are great cars though. Probably the only GM I would bother buying. Having said all that the 3800 is a masterpiece. I did have a chance to drive the supercharged version and it was pretty impressive.


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