Unusual Coolant Issue

[Don in VT]

Hi all,

This is for the coolant system gurus on the net. In the last couple of days I have noted a new a somewhat different cooling problem. My ZR is a 1990 that is box stock .

First some info.

1. Issue just started after 2 years of absolutely no problems with cooling or coolant.

2. My Tech and I have totally ruled out a blown head gasket.

3. I am using the good old and approved "green coolant".

4. Hoses are all new Samco and the WP is 2 years old.

5. There are no coolant leaks, anywhere and no coolant smell at all.

6. The system appears to be full with no air locks and the WP pulley is turning.

7. A new OEM NOS 180 deg thermostat was installed 2 years ago.

The Problem

When I start the car in the morning the temp gauge on the engine and system do not move after 3 to 4 minutes and there is no heat from the heater. When I remove the upper reservoir tank cap there is no flow in the air bleed circuit. After about 5 minutes both gauges begin to move up rapidly especially the system temp. At this point I shut the motor off and wait. I still have no heat from the heater. I go through this a few times and finally the temp will move to the correct reading and the heater hot air comes on and the car settles down to run normally for the rest of the days drive. I can shut it off and restart during the day and everything is OK until the next morning. My FSM and my gut feel would indicate that the thermostat is stuck closed but it doesn't explain all the observations.

Any help here would be appreciated.

Thanks

Don

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[Kevin]

when stats fail they generally fail open, not closed. Had a bad stat on my old DD honda, had no heat at all and the car would frost over save for a very small part on the windshield and the temp gauge never moved higher the 1/4".

[efnfast]

We had some bad thermostats floating around. I believe the spring had too much tension?

[WARP TEN]

We had some bad thermostats floating around. I believe the spring had too much tension?

Correct, but too little tension. Here is a link to Marc Haibeck's website page on the subject: http://www.zr1specialist.com/HAT%20Web/facts%20and%20failures/thermostat.htm

Bob

[GOLDCYLON]

when stats fail they generally fail open, not closed. Had a bad stat on my old DD honda, had no heat at all and the car would frost over save for a very small part on the windshield and the temp gauge never moved higher the 1/4".


Mine have always failed closed or partially open. However I think the OP issue is indeed a stuck thermostat

[mike100]

You may have to pull the thermostat to look at it. put it in a pan of boiling water and see if it opens correctly. I have seen more than a couple of thermostats stick open btw.

That doesn't explain the low flow AND the cool temps though??? The only thing that comes to mind is when I have seen bad water pumps with nearly completely eroded impellers due to cavitation from running straight H20 with lots of rusty water.

[mike100]

maybe its just open 10% and it delays the warmup, but really drive the car and it won't open all the way and runs hot- either way the thermostat is somewhat the easiest thing to take apart for exploratory work.

[Marc Haibeck]

Hi Don,

The air bleed system should be functional. In my opinion there must be coolant flow from the air bleed inlet into the surge tank. The cooling system on the LT5 is complicated. I suggest sticking with fundamentals and getting the air bleed system working. It might be clogged. There is a detailed description about how to find and fix clogged air bleed lines in the Heart of the Beast issue number 31.

A thermostat that is stuck open or closed will not have any effect on the flow of coolant through the air bleed system.

Best of luck.

Marc

[Don in VT]

Thanks everyone for the replies.

Mark,

I just reviewed my reprint copy of Heart of the Beast and I could not find any reference to the air bleed system.

List,

Does anyone have a copy of the air bleed system that Mark was referring to ? If possible could the section be scanned and emailed to me or better yet posted as a link ? I really do want to understand the air bleed design.

I started the car and got the same results. It just seems to me that the water is not flowing in the motor when the motor is cold. Perhaps it is the WP after all. Good thing I have a new WP and approved thermostat on the shelf.

I was only 2 weeks away from taking the ZR off the road for the winter anyway so it is no big deal but I do want to understand what is happening rather then just throwing parts at it.

Thanks All,

Don

[FU]

Heart Of The Beast issue 31
http://www.zr1netregistry.com/Portals/0/Newsletter/HOTB31.pdf

[Don in VT]

Hi

An update at 1:00 PM Vermont time,

I needed to use the ZR for a 1 mile trip to the store. When I backed out of the garage I left the car running while I went in the house to get something to take with me. When I go in the car I noticed that the heater was beginning to blow warm air. When I got to the store the temp gauges had just moved off low peg. When I got back in to go home the water gauge had moved up a bit the oil temp was still at the low peg. I decided to take it down the road a ways to check this new condition out and I found that the water and oil temp was moving up VERY slowly. Much slower then ever before. I drove about 10 miles and checked, by feel, the temp of both water manifolds and the cam covers and they seemed to be reasonable and not too hot. The water temp gauge worked its way up to 140 and the oil was about 110. On the water temp I usually run about 180.

Sorry for the long winded story but I now am convinced that I have a flakey thermostat and it is now stuck open. It may not be the whole story but I am going to change it out anyway.

More later

Don

[WARP TEN]

Hi

An update at 1:00 PM Vermont time,

I needed to use the ZR for a 1 mile trip to the store. When I backed out of the garage I left the car running while I went in the house to get something to take with me. When I go in the car I noticed that the heater was beginning to blow warm air. When I got to the store the temp gauges had just moved off low peg. When I got back in to go home the water gauge had moved up a bit the oil temp was still at the low peg. I decided to take it down the road a ways to check this new condition out and I found that the water and oil temp was moving up VERY slowly. Much slower then ever before. I drove about 10 miles and checked, by feel, the temp of both water manifolds and the cam covers and they seemed to be reasonable and not too hot. The water temp gauge worked its way up to 140 and the oil was about 110. On the water temp I usually run about 180.

Sorry for the long winded story but I now am convinced that I have a flakey thermostat and it is now stuck open. It may not be the whole story but I am going to change it out anyway.

More later

Don

In normal driving it takes me about 5-8 minutes to get oil temp up to 160. --Bob

[Don in VT]

Hi Warp 10,

Thanks for the input

Yes, my oil temp rises much slower then the coolant but my oil temp only get to about 130 tops. For the water temp I use the HVAC diagnostics to get the actual water temp. Works great and it is somewhat accurate as well.

Cheers,

Don

[Schrade]

If there is no flow the engine is air locked ...

Air 'locked'?

Does this mean that trapped air won't push through, and get 'burped' in a few drive cycles???

[Don in VT]

Hi All, Thanks for all the replies.

Replaced the thermostat. Bought the stat from Jerry's Gaskets so I know it is the correct one. Checked air bleeds, all clear. Thanks Mark H.
Runs great.

Installing 2 new wheel bearings later this week then the ZR is off to its winter slumber. Can't wait till spring.

Cheers,

Don

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