my 4100--what would you do
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HT4100 4.1, 4.5, 4.9 Discussion, my 4100--what would you do in Cadillac Engine Technical Discussion; 1985 Cadillac SDV, 136k miles, original everything (not considering pumps and maintenance items, of course). She purrs really sweet, never ...
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    ehall's Avatar
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    my 4100--what would you do

    1985 Cadillac SDV, 136k miles, original everything (not considering pumps and maintenance items, of course). She purrs really sweet, never any problems with stalling or anything. The problem is that she burns oil, not too bad but more than she should (may burn half a quart in a four-hour round-trip drive to the big city, or may only burn a quart on a cross-country drive). It also seems to get hot but I haven't hooked up a thermometer.

    I talked to a couple of guys locally, and they said my big options were rebuild, replace with a Jasper, or upgrade to a 4.5, with all three options costing the same $5k. I don't really like any of those options, and am trying to figure out options that are short of that.

    One other symptom is that the coolant seems to burn off or leak (no stains in my parking spot so I'm guessing burn). There is no milkshake. HOWEVER the car does not have the special coolant and tablets. I went through three water pumps in a one-year period and the last replacement did not use the correct coolant.

    I am thinking that maybe the wrong coolant and lack of sealant is causing some of the temperature problems, and the oil is burning out because the engine is running too hot. It might be that just flushing the coolant a couple of times will bring her back in good behavior. What do you think?

    If that's the case I am also considering some replacement parts that will improve appearance and performance. I might ought to get the head gasket replaced, and maybe do some fuel injection and distributor work for example. Anything else I can or should do here?

    The exhaust manifold is rusty, and I could probably get some better efficiency with a high-flow dual-exhaust setup, and probably get cleaner emissions from a high-performance catalytic converter as well. Any thoughts on this would be appreciated as well.

    All of the above would probably run $2k and if the coolant fixes my main problem (oil burn) then it will be money well spent.

    Or should I just go with a Jasper replacement?

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    awadecki is offline Cadillac Owners Enthusiast
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    Re: my 4100--what would you do

    I'd do a simple coolant flush on your car and install the GM seal tabs. This will probably cost about $65-80 at a shop. Put the tabs in yourself by grinding them up and dumping them in the radiator cap. This may help, or it may not. In any case, just keep driving it.

    I don't think it's worth it to put $2,000-$5,000 into an 85 SDV with 130k+ miles. Other things will start failing (power windows, A/C compressor, alternator, power lock solenoids, brake lines, master cylinder, etc.). Your best bet would be to take that $2,000 and buy another FWD Deville with under 50,000 original miles. You can easily find 85-87 Devilles on eBay with very low miles for under $2,000, and a bit more for 88-93's. This would be your best bet. Once the engine dies in your car, it's probably best to just let go.

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    ehall's Avatar
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    Re: my 4100--what would you do

    I already replaced that other stuff... lol

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    Re: my 4100--what would you do

    Awadecki speaks wisely. Of course, that's from a pure cost/benefit/good sense perspective.

    Whatever you do to bring your 85 up to snuff, you'll never get that money back in cash. However, sentimental types don't worry about details like that. If you like the car, there are a few things you can do less expensive than making Mr Jasper's house payment.

    First change the coolant and get the sealer in. Use old style green coolant. Flush with distilled water only, and use the upgraded GM concentrated tabs. They won't stop a leak, but they can help prevent them from forming. If coolant is already getting into the cylinders in quantity, you need to address that right away or your engine will shell out quickly.

    Second, change the oil and pay the $30 for an analysis at Blackstone Labs. They can tell you a lot about what's going on inside your 4100. If it comes back with elevated sodium numbers, you could probably get away with head and intake gaskets and get a few more years out of it. If there's serious metal particles, I'd just drive it til it dies, then invest in another low mileage example.

    Best of luck!

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    ehall's Avatar
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    Re: my 4100--what would you do

    I know I'll never get the money back, but that's not the goal here. I've had it for 20 years already and its a great car, if I can stick $5k into it and get another 5 years out of this great ride then that is a good bargain in my book. Will $10k get me another 20? Maybe. I guarantee you would love to have this car if its in the same shape in another 20 years.

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    Re: my 4100--what would you do

    When it's personal then the balance sheet matters not. Been there. If it were me, I'd look into finding an entire drivetrain out of a later model wreck. Maybe you can stuff in a 4.9 with later transaxle and electronics. If you can do the work yourself then it might be an alternative. If you don't have the time, space, expertise to do this then you are probably stuck with a stock replacement. Again, look for a wreck if you can. There should be some out there. The extra parts will pay for themselves over time. After some time you can always give up and dig deep into the pockets with a Jasper or similar.

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    ehall's Avatar
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    Re: my 4100--what would you do

    It has actually been burning oil for the last ~15 years, and has never really been much of a problem (just change it frequently, but no apparent issues). After this much time there may be some buildup that has not been washed away with frequent changes. I don't mind changing often, and that problem alone does not justify $5k fix.

    Loss of coolant is more recent. I would think that if the coolant was leaking into the engine then there would be discoloration from it coming back in but the coolant stays clean, just drops in level. Maybe the wretched water pump is acting up again.

    The immediate problems (slow off the line, hot but not so hot to sound the alarms) appear to be fuel system related.

    My point of decision here, if I want this to last another 20 years I will need to deal with the engine problems sooner rather than later, while replacement parts are still available. I don't think it actually NEEDS a new engine, but I would like to get rid of my problems, and I would like to do it sooner rather than later. However I also want to keep it as close to factory as possible--I don't want to tell the lady at AutoZone or wherever that I need a belt for a different engine, since that kind of complexity will be magnified as the years go by.

    With all that in mind I was looking at getting the existing engine rebuilt. But the cost is much higher than I thought it would be. It also appears that this engine has many many design flaws, so I would be better at getting a Jasper or upgrading to a later model (see issues above). On the surface the Jasper is probably the better choice, although I'm not sure that their 4.1 is actually a reman'd HT4100 or if its something else entirely--if I have to ask the lady at AutoZone for a Jasper belt that is even worse.

    Short term I think I will ask the mechanic to do 100k maintenance on it, clean and replace other important items, clean the valves from the top, etc., then think about it some more and defer large replacement for a while.

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    Re: my 4100--what would you do

    I think the best thing you can do is drain the oil, and the radiator fluid, and then change the gasket. then you can flush the oil out by running some fresh clean oil throught a few times, and flush your radiator out a few times with Fresh water. When you refill the oil make sure you dont use the oil that you did the flush with. Dont use the seallent tabs they tend to create clogs. if you want a good seal use some of that red gasket seal they sell all the way around. you should be good then.

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    awadecki is offline Cadillac Owners Enthusiast
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    Re: my 4100--what would you do

    I really wouldn't have someone at a shop rebuild this engine. Heck, I wouldn't even trust the mechanic at a Cadillac dealer. It has too many issues that many mechanics may just overlook (i.e. you should timesert ALL head bolt holes before resecuring the heads, securing the cylinder liners in place immediately after you pull the head off, gauging the cylinde liner height, etc.). Plus, in 130k miles, and after blowing water pumps and gaskets, the block may have warped slightly, in which case, you'll never obtain a good head gasket seal.

    Going with good rebuilder like Jasper would be the best choice. They have standardized processes that each engine must go through...it's not up to one person's discretion. I have, however, seen some AC Delco reman engines pop up on eBay from time to time for really good prices, still in their crate. It would be awesome if you could find one of those.

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    Re: my 4100--what would you do

    Mechanic said my fluid leak was heater control valve (may have heard him wrong but it's something silly like that). Compression tests show about 120 lb on all cylinders except one of the rear is only 85 lb. I told him if it is an easy repair go ahead, but don't take the engine apart (I am still thinking about replacement engine), and to change all fluids and filters and clean the valves from the top. The current engine should last another couple of years I'm guessing, which gives me plenty of breathing room to plot a long-term course of action.

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    Re: my 4100--what would you do

    im curious to see what she looks like ide love to see her....

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    ehall's Avatar
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    Re: my 4100--what would you do

    new carpeting and some other interior fixing next week--pics after that

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    ehall's Avatar
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    Re: my 4100--what would you do

    Got her back from the engine mechanic today, he said no evidence of HG failure. He replaced all plugs, wires, distributor, filters, fluids, and vacuum hoses, plus plus. About $1500 total. He said the engine was in good shape and should push another 100k miles. It sounds good too, and has a lot more power off the line. One of the rear cylinders is still weak but better (90lb of compression instead of 80lb before), so I think it's still prudent to investigate a Jasper 4.1 reman but I have a lot more breathing room.

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