A test of the cap can be a paper towel, zip tied around the overflow line. If it gets wet, the cap is venting at low pressure and you are also subject to coolant loss. The water pump alone produces 10 PSI plus, plus the expansion of the hot coolant. Normally would vent at 18 PSI.

As you must know, the oem gauge is wildly optimistic..

 

Sorry for the resurrection of this post but I'd like a last time help at my attempt to get this disco running cool. Here is what I've done:

Replaced thermostat with 180*f thermostat
Replaced fan clutch (verified working properly)
Replaced water pump
Replaced top radiator hose due to pinhole
Replaced head gaskets w/ new bolts (Verified heads not warped)
Replaced coolant reservoir cap
Bled cooling system (raised pass. side of vehicle and held bottle up while rad plug removed until no more air bubbles seen)

What I'm experiencing:
Normal raise to ~180-192*F during idle (~10-15mins, 100* ambient temp)
Raise to 196-202*F during fast idle (~5-10 mins, 100* ambient)
Slow creep 202*-216*F during 25-40mph (~10 mins, 100* ambient)

Once I go above the 202* mark the temperature will not come down and will slowly keep creeping up no matter if I'm driving any speed, idling, or stop/go. I'll shut it down before it goes above the 216* mark. No bubbles noticed in overflow during cold start to operating temperature. Once the temperature reaches 210+ the top radiator hose is VERY VERY firm. I understand healthy firmness in rad hoses once op temp is reached, this is beyond that. All torque specs / tightening sequences followed per RAVE and multiple How To's. All temps read with scan tool / live data. The only variable I could think of is the radiator, which seems to be newer than everything else in the engine bay. I really don't want to spend another $450 on a factory replacement.

Any guidance on where to go next? I really want to join the Disco club but this thing is driving me insane!

Thanks as always!!

 

Infrared thermometer. Point at warmed up radiator top and bottom on fins. If more than 10F spread, the lower rows are clogged. As it is a big D1 copper and brass radiator, a shop can unsolder side tanks and rod out the calcium build up. That is about $75 near me, you carry in. There are aluminum and plastic tank replacements for $240. Copper is mucho more.

Double check belt route.

Electric fans working when AC on?

Paper towel should hold against the grille, both sides, not blown away.

I just did HG on my 97 and it will do 183-187 down the highway at 60 with AC on. Mine crawls up when parked, I figure my radiator dried out during HG job, I should have taken it to rad shop while I was playing.

 

You say the heads are "verified" not warped, who verified this? Are you loosing any coolant and are you using coolant?

 

ihscouts makes a good point, because even with my compromised (IMHO) radiator I make good temperatures while driving at highway speed. Do you have any gurgle noises from the heater core and lines under dash? If heater core is bypassed you loose a good indicator of exhaust bubbles in coolant. There is also a $50ish chemical test that uses a liquid to "smell" the coolant recovery jug, and it changes color for exhaust gas. Does like 15 tests. Thermostat spring inside the block (you knew that).

Also, that $10 thermostat can come out and be tested in a pot of water on the stove to see when it is opening. You should also have a jiggle device or 1/8 hole in the flange, aligned to 12:00 position, to pass any steam pocket. Low coolant makes you not have heat (just steam in the lines), the heat gauge not go up too far (sensor is no longer immersed in liquid), etc.

 

A technician friend of mine checked with a straight edge / feeler gauge. Coolant level in the reservoir is EXACTLY the same after letting sit for 24 hours. I did notice a very short hiss for less than half a second when taking off the reservoir cap. Similar to when you pop the cap off a beer bottle. I couldn't tell if it was sucking in or blowing out because it was so short of a noise. Squeezed the top hose before removing cap to check if there was pressure, felt normal and full of coolant/water.

 

I never brought it up to highway speed (maybe 50-55 tops for 20-30 seconds) due to the actual highway being more than 10 mins away. No gurgling noises under the dash. Ran the chem test again (3 times, both cold and warm) and liquid stayed blue. Before the head gaskets replacement the liquid turned a deep green, which was enough for me to bite it and spend a weekend doing the gaskets. Thermostat is installed correctly. I put in a new one after head gaskets just for giggles, even though old one was still ok (verified ok with boiling water before install). I drilled a 1/8" hole and installed at 12 o'clock position per your info in another thread.

The top hose becoming very hard when at 212*+ is freaking me out. I'm sure the increasing coolant temps would cause it to get hard since it stays normal during idle and anywhere in the 200s. I idled it today for an hour and the temp never rose above 196*. If i fast idle / drive it around the block long enough to reach 202* it seems like the cooling system can't dissipate the heat enough to coolant it back down past that point. I can fast idle to 199/200 and it will go back down and alternate between 192-196*. Anything above that it starts to creeeeeep.

Thanks guys. If you're ever in my neighborhood I owe you a few rounds of beer.

 

Radiator

 

Almost ready to make the jump and get a radiator. However, I noticed today that there are ZERO bubbles in the reservoir tank when idling and revving up to 2k rpm, cold or warm. BUT I do notice tiny pin head bubbles for a about a minute after revving past 2,000rpm and even give it a good few high rpm revs. This may be a game changer . Thoughts?


Thanks again

 

If you want to know where those bubbles came from, you'll need the chemical block leak test. It is a liquid that reacts when exhaust gas is present in the coolant and changes color. ABout $50 ish. Does like 15 tests, so a good proof of performance for testing after head gaskets or other major repairs. The little tiny bubbles could be steam passing thru the system. Like a pan simmering on the stove before the roilng boil begins. Do you have any coolant loss?