Im going to try to explain this the best I can. For the past 3 weeks I have slowly been loosing coolant. I have had my car pressure tested and all turned out fine. I also tried the Lisle coolant tester and there were no signs of anything in my coolant. I've had the car up many times and everything seems bone dry. Both my surge tank and overflow are full. My question is, after my car gets to operating tempature should the overflow dipstick read hot? Also I have read many times that you guys run your car without the rad cap off to check for bubbles or get all the air out of the system etc. Would the coolant not overflow when doing this because mine does. My car does not run hot at all. It will idle for about 15-20 min before the fan kicks on. I flushed out the coolant last year by attaching a hose to the coolant line and letting it all drain out. Did I possibly miss somthing? My intake gasket was changed last year. 90 L98. Sorry for it being kinda long, I just wanted to give all the info I could. Thanks

 

If I were you, I'd try a new radiator cap!!

 

I did buy a new one last year. If the rad cap was bad wouldnt the pressure test find that out?

 

Sounds to me there still might be air in the system if your not loosing coolant by leaking. If the system has air trapped it usually will run hot and you will keep adding coolant to the system. Have you taken the cap off and idled it at about 2,000 rpm to get the air out. Can't think of anything else from you description.

 

I thought of doing that but with my cap off the coolant will overflow. After 3 weeks wouldnt all the air leak out everytime I take the cap off?

 

Ive heard of drilling a hole in the rad cap then going for a long drive. Is this the best way to get air out? Won't coolant spill out?

 

The radiator may have an air bleed or plug on top of the tank or the side, and if it does, open or remove it. Next, open the drain ****. Collect the coolant in a pan.

Next, disconnect the lower radiator hose from the radiator and let coolant drain from the block.

Third, disconnect the hoses from the heater core, attach auxiliary hoses to the core necks and force a garden hose nozzle into one hose. Run plain water through that hose until clear water comes out the other.

If there are coolant hoses connected to the intake manifold or thro ttle body, disconnect them at the other ends, and allow the part to drain.

Finally, empty the overflow reservoir into the catch pan.

Measure the coolant drained from the radiator, engine, manifold or throttle body and reservoir. If you've collected at least 90 percent of the cooling system capacity, and the coolant now is clear, you're ready.

If it still has some antifreeze dye color, slowly fill the system with plain water, with all air bleeds open. Dispose of the coolant in an environmentally responsible manner, please. Call your local fire department for advice.

As water oozes from an air bleed, close it, then keep filling. When you've filled the system, top up the reservoir and run the engine un til it's warmed up. Turn on the heater to be sure the heater core is flushed.

Let the engine cool, drain the radiator and if the coolant is clean and clear, you're ready to fill. Disconnect the lower radiator hose and let the water drai n from the engine too, so that the drained amount is at least half the capacity of the system.

Also, draining the reservoir should give you a margin. Add an amount of your choice of antifreeze yellow/gold, green or a "retrofit" to orange–equal to any percentage between 50 percent and 60 percent, and then top up with water.

Always fill a system with the front of the car jacked up as high as possible, and all the air bleeds open . When coolant oozes from an air bleed, close it and continue filling. Air rises to the top and the jacked-up front will help purge air pockets in the system. Fill slowly to allow trapped air to escape.

Complete filling of a system can take lots of " thermo-cycling"–warming up the engine and letting it cool down–to purge all the air pockets, and, in fact, you may have to recheck the system over a period of a week or more of operation.

Some systems are so difficult the factories provide very specific procedures, so check your Helms factory service manual for instructions.

 

Thanks for the detailed walkthrough. I pretty much followed that exactly last year when I drained my coolant. Maybe I should do it again.

 

I have a very weird update everyone. This morning when I checked my coolant level, as soon as I took the rad cap off it overflowed. The car sat all night so there should barely be any pressure in it to overflow. Any ideas? Thanks.

 

Sounds like you have an air pocket trapped.

 

This does sound like air to me also. You can take the radiator cap off and start the engine. Idle it til hot at about 2,000. You will probably notice a drop in coolant and bubbles coming up (the trapped air). There are no air bleed screws on the L98 TB as is a LT1. This is easy...give it a try if you haven't already.

 

I drilled a very small hole in the flange of the thermostat.Now it bleeds perfectly as the engine heats up and any trapped air escapes..Cured my problem.

 

I've ran the car with the rad cap off many times. After the car gets around operating temperature it boils over.

 

Is your thermostat sticking maybe?

 

I bought a new one last fall so I would think no, but I guess anything can happen. So you guys are telling me that I should be able to have the rad cap off when my car reaches operating temperature without anyting boiling over?

 

Yes, you can take the cap off then start the engine. Keep an eye on you temp guage just in case. You should notice some bubbles and the coolant getting lower (if there is trapped air). DO NOT take the cap off after the engine is warm unless you want hot coolant all over you. I saw here on the forum where someone (won't mention any names) said to take the thermostat out and put it in boiling water and see if it opens. Well the thermostat is cheap enough, that if I went through the work to get the old one out, I would install a new one. Sometimes you can over troubleshoot.