can intake manifold gasket leak cause bad mileage?

holy cow, on closer look: what I'd thought was a low level of coolant on this slim-style reservoir is actually right on the 'Cold' line. The reservoir should be mostly empty, with just a few inches of coolant on the bottom. The coolant in there looks dark, but not thick. The radiator cap is clean, and there is only a bit of sludginess floating on top of the visible coolant. That's good news.

Also, the engine oil itself is not milky, and the level is not overfilled (so coolant had apparently not gotten into the oil).

So I guess I should go with a flush and fill. But should I use Dexcool or switch to something else like the Prestone Long Life? I've read about that for hours yesterday and there doesn't seem to be a conclusive answer.

One big question occurs to me: do I not have a problem at this point because of the low miles (15K)? If so, why don't the years matter (since late 2002)?

Also, I still have the problem of the sudden reduction in mileage...

Have a competent tech plug a scanning tool in and look at the fuel injection parameters... if something is leaking on the intake, it'll show up with some goofy numbers.

A can of WD-40 or an unlit propane torch can help find the problem.... if you get it near the leak and it sucks it in, the engine will race.

I doubt anyone will do anything for free today, and I wouldn't trust anyone who did. If they're not charging you anything for diagnosis, they're damn sure going to find _something_ to charge you for.

--scott

If it's not broken, don't fix it.

If you haven't had any problems with the DexCool (and I'm surprised you haven't because everyone else pretty much has), keep using it and don't change it.

If it has never been flushed in eight years, it's way overdue. I'd consider brake and maybe even transmission fluid too.

--scott

How are you measuring that? Are you sure?

I don't know about the Dexcool because I've avoided it, and heard it causes problems. But I've read that turbulence has some effect, so the more miles the more turbulence. My '97 Lumina 3.1 had Dexcool in it when I bought it with 105k miles. Now has 150k miles. Here's what I did when I bought it. I drained the Dexcool out by pulling the lower rad hose. Put hose back, filled with water and ran it hot for a while. Think I opened the rad petcock and used a garden hose to keep it topped off for a while. Didn't get too anal about it. When there was no yellow left I was done. Pulled hose again to drain, then put on new hoses and thermostat. Filled with a 50/50 of the Prestone green stuff, and added a pack of the GM cooling system sealant pellets.

5 years ago. So far so good.

First make sure your milage check is accurate.

32mpg is near tops for highway on mine. I never checked city closely

- too many variables. Seem to get around 18-20. You might have a miss somewhere, or a bad injector. Hard to tell. If they are original plugs/wires you should replace them. I'd do the wires first. Plugs might be fine. Might be worth it to have a mech hook it to a diag machine. Eliminate the guesswork.

--Vic

ps Sorry I sent a reply to your e-mail.

The problem in the mileage reduction could be due to a LOT of things. Sitting that long the interior of the muffler could be rotted and blocking the system, Mouse may nave gotten to the wiring and caused problems. Fuel lines may have developed a leak due to rust. Injectors may be clogged due to crap in the fuel lines from sitting.

Low mileage is NOT really a good thing sometimes.

As for the Dexcool. Change it out and flush the system and put in fresh coolant. The bad rap that Dex gets is NOT due to the coolant itself. It was due to how it was marketed by GM. They claimed it was a lifetime coolant when it really isn't. It still needs to be changed out and the system flushed every 4-5 years to prevent problems.

Personally I use the universal type coolant Prestone sells. Then just note that it will need a flush and fill in 3 years. When you look at what it costs to do a flush and fill versus what it costs to replace plugged or damaged parts it's REALLY cheap...

Oh and my usual routine on my vehicles is to drop the coolant, flush the system. Then while clean water is in the system, pressure test it for leaks. Drain everything including the block. Then change the thermostat and the water pump out, inspect the hoses close and every second flush replace them, new serpentine belt as well. Being that I keep vehicles a LONG time this is just cost of ownership.

Prestone and Bar's Leaks.That is what I always use.

cuhulin

Prestone long life and Preston "all makes all models" are just DexCool clones and contain the same chemical (2EHA) that is in DexCool and softens intake gaskets.

If you want to be really safe, you should have the lower intake gaskets replaced anyway. DexCool has already attacked them, and from my reading I gather that they tend to fail on those engines eventually pretty much no matter what.

As for alternative coolants, G-05 seems to be the best/safest alternative to DexCool. Zerex sells it (gold bottle- sometimes hard to find) and you can get it from any Ford dealer (Motorcraft Premium Gold) or from any Chrysler dealer (Mopar G-05, which is dyed red instead of gold like Zerex and Motorcraft). I also hear good things about Peak Global Lifetime coolant. You could also use old-style conventional silicated coolant and change it every 2 years like the old days. But it is getting very hard to find now also.

You do realize that Prestone completely changed formulas a few years ago, right? They don't make a conventional coolant any more, only their "all makes all models" coolant, and it is a clone of DexCool.

I always change the radiator fluid once each year.Usually just before Wintertime.Years ago, some people used to change radiator fluid twice each year.For Summer time and Winter time. cuhulin

Irrelevant. If you're using Prestone, you're just putting in fresh

2-ethylhexaonic acid to keep dissolving gaskets every year.

I never have had any gasket problems (Knock on Wood) with the many old clunkers I have owned over the years, since 1957, in 1957, that old car was a secondhand car too.I don't remember which brand name of car it was, it was about six years old when I bought it in 1957.I will keep on using Prestone, Bar's Leaks too. cuhulin

So if you'd always bought Borden milk, and then one day Borden started selling milk substitute made from manufacturing waste instead of cow's milk, you'd just keep buying Borden?

The whole point is that Prestone isn't Prestone anymore. I used it exclusively from the 60's until the formula changed, but I don't use it anymore. If you want to stick your fingers in your ears and shout "LALALALALAICANTHEARYOU" go right ahead.

What you said about the green Prestone being almost the same as Dexcool was news to me. What does that mean for eating gaskets, if that was a real problem with Dexcool? I've always removed the Dexcool more because it always looked sludged up than for any other reason. Does the Prestone green do this too? I think I've read that's it's mostly exposure to air in vented overflow tanks that cause the sludging. I still have those tanks on my cars, but tell the truth, I don't change the anti-freeze much after the initial hose/fluid/thermo replacement I do when I buy a new used car. Might add some because I do a water pump. Usually only have a car 5-10 years because it rusts out. The overflow tank on my Lumina looked nasty when I flushed out the Dexcool, and is still stained, but I haven't looked inside for a few years. I think I'll check it.

--Vic

I haven't found anything really definitive, and it will probably be hard to do. DexCool was manufacturer supplied, and lots of its issues cropped up under warranty. Prestone is aftermarket, and there's not nearly such a good information gathering system on it. But it DOES contain 2-EHA, the acid implicated in damaging (not really eating, just plasticizing/weakening) intake manifold gaskets on GM cars. It may also be prone to sludge formation in air, but its also possible that other additives in the Prestone keep it from doing that.

Personally, I don't believe in anything that says its "ok for all makes and models." That means its not really *right* for any make or model :-p

As for DexCool alternatives, Mopar/Ford/Zerex G-05 seems to be very safe and effective, but that's also based on anecdotal evidence. Some evidence exists that the "Asian vehicle" coolants (phosphated OAT chemistry) might work well too, but you have to be careful because some of *THEM* contain 2-EHA. G-05 does not. Another coolant that is often recommended is Peak "Global Lifetime," but its somewhat hard to find and often confused with their "long life" coolant, which is a different chemistry and is also similar to DexCool. Lots of good debate (and information buried in the debate..) can be found on the cooling system fluids/additives section of the bobistheoilguy forums.

The other bottom-line fact is that DexCool seems to be just fine once GM got all the requirements sorted out- it should only be used in cooling systems where the overflow tank is pressurized and not with the more common type where the overflow tank is open to air with only the radiator being pressurized, and it should only be used with specific types of gaskets if the gasket ever touches cooling passages. If those conditions are met, people rarely seem to see an issue with it.