Hoping for some help here. My car has been leaking coolant for quite a while now. It also overheats when sitting in traffic or driving less than about 30 mph. Sometimes, it doesn't leak at all, other times it pukes out about a cup or two of coolant after parking. The leak is at the front of the engine somewhere. I don't see any leaks or evidence of a leak from the front. The only sign I can see is on the bottom of the cross member at the front of the engine where the two braces are. There are always a couple of drops hanging there when I go under the car. The only things I can think of are the lower rad hose, water pump, or freeze plug on front of block. I bought a new water pump and went to install it Sunday, but it took so long to break the pulley bolts loose, that I didn't have time to finish the rest of the job, so I put it back together until I have an entire weekend to devote to it. Given the symptoms, has anyone had a similar experience that may be able to help me pinpoint the problem? Thanks for any help!

I have pulled the radiator and cleaned it out and also replaced the intake gasket as it was leaking from there previously. Also replaced the 2nd fan as it wasn't coming on.

 

sounds like you are on the right track with the waterpump. your overheating may just be because of low cooleant from the leak

 

Make sure your radiator is clean. After 25 years, they look like the picture
Mine leaked like that. Wound being water pump gasket went bad

 

I keep it topped up and it overheats either way, full or partially empty. Like Sunday I emptied the system and refilled it. Last night on the way home from work (only one small drop on floor of garage and none in parking lot at work), I got stuck in some traffic on the freeway and it started going up in temp.

 

Radiator is clean. I was thinking it had to be the water pump because of the intermittent nature of it. If a freeze plug or hose, you'd think it would leak all the time. Not sure how the pressure plays into it. I could have sworn I had my finger on the bottom of the two sides of the water pump and couldn't feel any moisture. No moisture at the weep hole either. Pump looks newer than the rest of the components on the engine, but I've had the car for around 10 years now, so it's not new or anything. Oh, yeah, I did put some stop leak in it several years ago before I changed the intake gasket, if that helps.

 

Do you have a FSM set?

I'm curious...what do YOU call HOT??

'cause heres the painful truth....

Normal temps for that engine on a day that's 90 degrees outside with YOUR a/c running while stopped in rush hour traffic.....
230 degrees.

Put that same car in Phx Az in August and push that to 240 or more.

Even in moderate climates....normal while sitting still is 220. Cruising temps should be 195 to 210.
It should creep upward when in traffic. There is no air flowing TO the radiator, and the water pump is NOT circulating any water. Idle with summer temps is more stressful than a 1/4 mile run.


You need to see the maze of heater hoses that live UNDER the a/c compressor mount. There are metal fittings, both aluminum and the usual steel. These rot out and leak, and the rubber gets hard and leaks because no one even knows its there.

That's a GREAT place for leaks. Hard to spot, leaks are hidden, can't be seen.

To change a water pump on a L98 requires a full afternoon IF you have all the tools and misc hose clamps, and fresh heater hose right there. Basically, you strip everything off the engine face, compressor bracket and other brackets that are ON the water pump, then get the pumps 4 bolts off...

The a/c bracket "pulley" bolt............... Valium.

Once you start getting into the compressor bracket you will see the heater hose T and merger of return lines from heater core and oil cooler (if equipped). There is one that is under 3" in length...

On your new pump, something that others have done to help in future diagnosis, install a fitting in the pump bearing "weep-hole" and run a small hose from there to a place where you can SEE if there is water leaking out. This also helps prevent trash from entering the hole.

While its apart .....IIWM, I would get a better pump. You have a marginal cooling system even when its at its peak performance. A tired clogged radiator, a avg pump, and any sort of a leak that prevents the system from holding pressure will easily cause overheating.

You will end up replacing the radiator. These are disposable. A new 2 row that's twice the capacity can be had for <$250 for an aluminum knock-off brand that will serve a stock engine just fine. Or you can go BIG BRAND for $400..your call.

The one thing that EVERYONE agrees on is the pump...
A 'nice' pump that's got a "cast" impeller will cost $150- $200 but its worth it. The stock pump has a 'stamped' impeller that will move water, barely.
The cast impeller pushes water thru the system making it 10 times move efficient.

Spend the money. That's one step closer to a stable cooling system and summer temps.

BTW,
if you just want to replace the radiator with a new stock unit, they are only $75....the stock rad works when its new. Its just not going to support much in the way of upgrades to the engine.


FWIW,
the "pusher fan" up front is as useless as lips on a wood pecker. It was installed by the dealerships on the instructions from GM when the public failed to comprehend that EFI engines run HOT. Accept it, like it, cause that's the way it is !
This fan does not come on until the system reaches 238 degrees, and then it only supplies fresh air to the a/c condenser. The design of the "air-box" does not allow air to flow thru the condenser to the radiator. It must go around thru the baffles and the pusher does not do that. Its flow is aimed AT the condenser. If you notice, about the time your engine is getting warm...the a/c wants to quit cooling. That's because the condenser can't dump off the heat its collected from the cabin. The pusher fan does that, pulls that heat away so the cabin cools again. That heat is NOW sent directly to the radiator. Think you're gonna see temps below 220 in the summer? nope.

 

Thanks a bunch for spending the time here. I appreciate it very much. This is usually my daily driver with a 100 mile round trip to work, so I've driven it in all kinds of weather. Summer is definitely the worst. For the first couple of years at least, I didn't have any overheating problems, even when poking around on a hot summer day, just a little warmer than usual. I've pegged the gauge a couple of times and finally figured out that if I turn the heater up all the way, it will stop short of the 260 mark. It's no fun sitting in 90 degree heat with the heater on all the way. Thankfully it's a convertible. I do have the FSM set and hot, well, is hot. It normally runs rock solid even on hot days at around 200 as long as I keep it moving. I'm going to take your advice and wait until I can afford the more expensive water pump. I hate puking antifreeze puddles where ever I go, though. I should be able to find the leak once I get things torn apart. Just want to make sure I'm on the right track. I'm pretty sure that the loss of pressure due to the leak is what is causing the overheating. But, I could have some blocked passages from using the stop leak as well, I suppose.

 

Go to your local Advance and borrow a pressure tester. Then get a good flashlight and start looking

 

What's that going to tell me? That I have a leak? I've done the flashlight thing a few times. There's nowhere that I can put my head where I can see the source of the leak. There's simply too much crap in the way to be able to see it. Thanks for the ideas, though.

 

a mechanic mirror

 

A pressure tester will tell you if your cooling system is holding pressure.

If your system isn't holing normal pressure, your coolant will "boil".
That "might" be why your cooling is boiling over.

Coolant will boil at a higher temp, the higher the pressure.
Normal cooling system pressure should be in the 10-15 psi range

 

There needs to be a firm diagnosis.
It probably IS the loss of pressure due to a small leak that's causing the temp to spike...and yeah, anything over 240 is TOO HOT.

You will do well by getting a better quality pump. Most "nice" pumps move as much water at idle as the stock pump moves at 3000 rpm...BIG difference.
Add an all aluminum radiator and you're ready for a summer in Sonoma...(the car anyway..)

But, if there is STILL some sort of coolant loss, all that's in vain.

I would confirm that there is NO internal leakage. That's easy enough.....

On the L98 you take the belt off. Take the radiator cap off. Start the engine and idle.

LOOK inside the radiator and watch for ANY movement. Bubbles, water flowing. Water moving ANY at all.
Rev the engine a few times and LOOK.

There should be NO MOVEMENT of the coolant....NONE, NADA.
the water pump is the ONLY connection mechanically between engine and liquid. Take the belt off and the water has NO WAY of moving...

if it DOES<> that is evidence of a failed head gasket or some other means of pressurized gases entering the cooling system and moving the water.
If all is well in that motor, you can rev it and the water should sit perfectly still...motionless. Yes, even with the thermostat installed.

I'm NOT suggesting that you have a gasket problem,. I'm telling you how to eliminate that from the possible things that can cause coolant loss.

I'm still a big fan of that heater hose mess leaking under the a/c compressor....
that's a cluster-tuck if ever...

Good luck,
I'm sure you'll figer it out. The FSM has some good tips on tracking down slow leaks and misc coolant loss. Follow the GM guide to pump replacement and it'll go good.

 

It's a start. You have to find the leak somehow unless you're content with throwing parts at it