98 Blazer 4 door 4wd
Since l had the lower intake manifold gasket replaced, l have had to add coolant about every 100-150 miles. Anyone know why?

 

How does your oil look? Is there any coolant in it? Does it smoke out the exhaust? Are you leaving puddles when you park? There are only a few places leaking coolant can go.

 

A good way to check for coolant leaks is to use a coolant system pressurizer tool. You can often borrow these from local auto parts stores or buy them at Harbor Freight.

To use them, with the engine cold, you replace the radiator cap with the tool and use the hand air pump to pressurize the system to the pressure rating of your radiator cap. Then you wait a bit and look for leaks.

The reason for starting this when cold is that coolant can leak and then evaporator if it drips onto a hot surface leaving no clue to where the leak is located. This is obviously safer too due to the lack of hot surfaces on which to burn yourself! I believe there might also be ways of adding dye to the coolant that will shine with a UV light, also a tool that can be often borrowed from a local auto parts store.

If this fails, the you should try it with the engine at operating temperature but with the engine off. With the engine off but hot, a leak could open up and/or you might be able to hear the coolant turning into steam when it hits a hot surface.

Tom A pointed out an important point that the coolant could also be leaking into the lifter valley or the cylinders. The former would cause mixing of the coolant with the engine oil and the latter would cause steam to come out of the exhaust.

BTW, I had a friend take her 4Runner to a shop to have the radiator replaced and long-story, short, the shop forgot to tighten the clamp on the lower radiator hose where it attached to the water pump! Sometimes the problem is stupid stuff like that.

 

How would I know if there was coolant in the oil?

 

If there was coolant in the oil, the easiest way you'd see it is by what is on the dipstick when you pull it out. If the oil and coolant had been mixed a bit, it can look a bit like chocolate milk. If not mixed, you will see drops of coolant beaded up on the oil of the dip stick. Then if you suspect that coolant had gotten into the oil, you should drain the oil and confirm if any coolant also comes out too, either mixed with the oil or along with it.

As for checking for a leaking head gasket, I forgot to mention that a way I've seen this confirmed is to do a coolant pressure test on a cold engine and insert a borescope through the spark plug holes to look for coolant accumulating on top of the piston. This should be done if you suspect a bad head gasket from excessive white "smoke", actually steam, coming from the tailpipe.

 

I've lost coolant from three places. A 20 year old heater hose had a crack in it near the clamp. Leaked for months (as seen at the reservoir levels) and finally one day busted open about a mile from home. Radiator: crack on top leaked when the pressure built up. Couldn't figure it out till one day it cracked bigger. 3rd was the LIM, the RTV that sealed it to the block in front (behind the thermostat housing) leaked for quite a while till finally more sealant gave way and you could see the water running out and down.

Given how you just had the gaskets there replaced, my guess is the mechanic was not sufficiently careful. The RTV needs to be laid down at the right thickness and the manifold set down very exactly for the seal to set up properly. A flashlight and some paper towels should reveal a leak there, if there is one.

 

The oil looks and smells like oil. I don’t have a garage so l can’t check the exhaust for steam until the outside temperature is over 50 degrees. I have small puddles of antifreeze in 3 or 4 spots around the perimeter of the engine.
Does that indicate the leak is from the seal of the LIM manifold? If it is, then is it ok to drive it an keep checking the coolant?

 

Reading this, it occurred to me that another source for leaks could be the engine block freeze plugs. I had a leak at the one of these that had been replaced with a block heater.

But back to the LIM, the little puddles of coolant from around the engine is could be because of a leak in the LIM but it is definitely not conclusive.

I'd not be comfortable driving around with an unknown leak in my cooling system until at the very least it had been properly diagnosed. Only then could I conclude that I could drive around without having to worry about a catastrophic leak later happening.

Have you looked into using a cooling system pressure tester and UV dye to try to identify the source of the leak?

 

98 Blazer 4dr 4wd
I looked to see if there was coolant on the lower part of the engine with a flashlight after driving. I don’t see any fluid. Where is the lower intake manifold gasket? Is it below the spark plugs? Anyone have a picture of this?

 

The lower intake manifold (LIM) gaskets are marked as part number 501 in this diagram.

They reside between the lower intake manifold, and the cylinder heads. Note that in this diagram, the upper and lower intake manifolds are shown as one, part number 500.

There are water passages at the front and resr holes in the LIM gaskets. The other three large passages are for the air inlets for each cylinder.

When instslled, RTV sealant should also be applied along the top of the walls of the block at the front and rear of the block.

The leaks would originate near the frontor rear of the cylinder heads where the water passages are located. This would be very unexpected if the gaskets were instslled correctly.

https://nemigaparts.com/cat_spares/e...t/00/ts00-665/