4.1 liter idea. Would appreciate your opinion

[kdaddy]

I need your HONEST, PROFESSIONAL, and SINCERE opinion.

Ok, I have just purchased an 84 coupe Deville in GREAT shape. Body is excellent, no rips in the leather, no sagging headliner, no cracked armrests. In other words a great buy. BUT! it has the HT4100 with 109,000 miles. Everything runs 100%

OK, here is my idea............ I decided I would purchase a brand new water pump and a "Medium" temp thermostat to help prevent the dreaded overheating of the aluminum V8 which would lead to its well known demise as we ALL know about. Also, I decided to give it a tune up and retard the timing 2 degrees less than the BTDC suggested for this vehicle. Am I crazy or is this a good idea to help prevent possible overheating. Of course changing the water pump is a good idea with that many miles on it. However, I do know that changing to a med temp thermostat would prevent the engine from reaching its optimum temperature and would result in a slight decrease in gas mileage. To me this is OK if it helps prevent the dreaded head problems. Also, retarding the timing would also decrease internal combustion temp and like above would decrease the gas mileage slightly. I guess what I am asking is if this is a good idea to do these "slight" tweaking to the engine in hopes of preventing overheating. Also, I forgot to mention that I bought the GM stop leak pellets also. Tell me what you think please. I would hate to be doing something that would have no benefit or even worse be detrimental.

[Cadillac Jim]

CONGRATULATIONS

Congratulations on the acquisition of your 84 Deville, and welcome to Caddyinfo. Browse around the web page and forum areas. You will find the forum and its pages interesting, informative, and all of our members are gentlemen.

DON'T CHANGE ANYTHING OUT OF SPEC

I wouldn't change the thermostat to one not recommended by OEM or change the spark timing. If nothing is wrong, it will simply run the engine out of specification. If something is wrong and the car is overheating, it won't help.

Changing the water pump is your call. Be sure and get one that is OEM quality. There are a lot of bargain water pumps out there that don't last.

The 4.1, 4.5, and 4.9 do not have an overheating problem, to my knowledge. Others here that drive these cars will chime in with their experiences and opinions. Here is my opinion based on my experience with my 4.6 Northstar and many other previous cars.

MY OPINION

The first thing I would do is to have the coolant tested for age, freeze protection, and combustion products at a radiator shop or good mechanic. The test takes a couple of ounces of radiator coolant and a few minutes of time, and is inexpensive. These tests will show:

• The antifreeze is not too old to protect against corrosion. Green anti-freeze is rated at two years.
• The coolant should protect against freezing to at least -34 F. This is 50-50. It shouldn't be over 60% antifreeze.
• The combustion products test should show that the head gasket is not leaking.

Then, unless the first test shows that the anti-freeze is new, I would change it. For any used car with aluminum engine parts, this is just as important as an oil filter change and lube, and a check and change of the belts and hoses.

OVERHEATING

The 4.6 Northstar does not have an overheating problem either. The cooling system on these cars does an amazing job of keeping the temperature stable no matter what, so long as enough air is going through the radiator.

An overheating problem on any Cadillac means that there is a mechanical problem. On Nothstars, it usually means that the antifreeze got too old a year or two previously and corrosion got into a head bolt thread, and a head bolt has pulled out. Once that happens, the car will begin to use coolant and overheat, and nothing will fix it except a head bolt repair. This is well known. It is a maintenance and repair issue, and is not an overheating problem.

[Dave in Texas]

I have that engine, but the '87 build-year. To my knowledge there has never been any major problems with the 4.1L. What problems did occur were because of poor maintenance, by either the owner or the dealer. The cooling system failures resulted from the maintenance schedule not being followed and the tabs not being used. Maintain the cooling system properly and change the oil/oil filter at 3K intervals. Do not go out of 'spec' with anything. Use OEM replacement parts when parts are needed. Now that your 23yr old car is almost broke-in, it will be fine if you treat it right.

[coolnesss]

I had an 84 Eldorado with the 4.1 and drove it for more than 100k miles, and the cooling was fine the whole time. I loved the car.

The one thing that became a problem was that it started losing power inexplicably, and after throwing money at mechanics for awhile and not resolving the problem, one of them said he had consulted a cadillac pro who said: use marvel mystery oil in the gas - I forgot what the condition was that he said it cured - but, I did put the MMO in the gas at every fill up for a few weeks and, strangely, the problem was solved and she ran perfect again. The guy had said that as they age, you have to put MMO in the gas once a month or so and it will remain trouble free. I did for another 30k or so miles, and the car ran perfect. So, I recommend that treatment.

Get the transmission serviced though - at 100k miles it'll need it.

Enjoy the car - they are wonderful in those years!!!!!

[Cadillac Jim]

Transmission service is NOT a flush. It's dropping the transmission oil pan, cleaning it and the filters, etc.

I think the MMO gas treatment cleaned the injectors. They may have been clogged, leaky, or sticky, or any combination.

[Patrick7997]

Dave must be a little confused.... the HT4100 is possibly the darkest chapter in the History of the Cadillac Motor Company...

That being said, Jim is right.... changing things around is not going to help.

The proper Preventative Maintenance is critical to get as much as you can out of it... radiator fluid changes being a big key, you can't do that too often....

And yeah, don't flush anything. Drop the pan, drain, replace filter, new gasket, replace pan, use a torque wrench on those pan bolts, don't strip them, refill with proper fluid...

There used to be several places that did decent quality rebuilds on HT4100's, with warranties... you might look into that, if it becomes necessary.

Congrats on the car though, seriously. I like & admire your positive attitude, and desire to get as much as you can from it.

Clearly, we'll never know how many of these died from neglect, and how many died from other factors... In the mid 80's, they were notorious... but if you do your part, stay on all your preventative maintenance, you'll give it the best shot possible to live a long healthy life.

[KHE]

Forget about the lower temperature thermostat and retarding the timing... just change the coolant and always be sure to use the sealer pellets and you should be fine.

[kdaddy]

Great responses! And yes everything is fine with the car. So I will just do standard maintenance then and forget the "tweaking". As for the car being serviced I bought the car from an old man. Yes, sometimes that old worn out story is true and in this case IT WAS TRUE. So that being said I guess I scored good. In the spring when I pull it out of the garage and I will post some pics. I will NOT drive it in the winter. I live in NY and winters will destroy your car. So in the meantime I will continue to drive my front wheel drive Buick LeSabre until March.

Kdaddy

[jackc]

Congrats on the purchase. These are beautiful, comfortable cars, and the 4100's aren't all that bad if properly maintained.

For service, be sure to check the belts or go ahead and replace. I chunked a belt on my 83 Eldo and overheated it BAD before I realized what was happening. The idiot light is almost impossible to see in daylight.... But even the overheat didn't hurt the engine. So enjoy!

[Texas Jim]

I had a 1984 Fleetwood Brougham that I put about 125,000 on before I sold it. Had ZERO mechanical problems with engine and transmission. Did put a water pump on it at about 100,000. New belts and hoses also at that time. At about 75,000 put a new idle speed solinoid on it.

Other than that, basically just put gas in it, changed oil regularly and drove it. Except for being underpowered, it was a very good car. Still very tight body and drove very good when I sold it.

[KHE]

For service, be sure to check the belts or go ahead and replace. I chunked a belt on my 83 Eldo and overheated it BAD before I realized what was happening. The idiot light is almost impossible to see in daylight.... But even the overheat didn't hurt the engine. So enjoy!

I agree - it would be a good idea to replace ALL the belts if there are no records on when they were last changed.

[Cadillac Jim]

Don't forget to change the hoses. The A/C hoses are neoprene and are probably OK forever but look at the heater, bypass, radiator, and all the vacuum hoses.