troubleshooting coolant flow

[RJM1000]

Hi I have a 95 1L metro, I've been reading the posts and trying to troubleshoot this coolant- heat issue I've been having,... basically, sometimes my cabin heat works and temperature gauge work and sometimes they don't, even when I know the engine is hot, the guage will drop right off down to the very bottom like the car is turned off, when this happens, I find that the heat dosent work and the top radiator hose and the hoses going to the cabin heat exchanger are cold. This is not a minor flucuation of engine temperature due to the fan turning on and off. (I just checked the thermostat in water on the stove and its good, and I just put a radiator in and a new water pump and there is no coolant leaking out anywhere..... so I think that this tells me that sometimes the coolant is circulating and sometimes not, and this dictates when my cabin heat works or not... this sounds like I have a blockage somewhere maybee? I checked for blockages in the rad, thermostat, cabin heat exchanger, all rubber hoses,.... is it possible to have a blockage in the engine block somewhere?? any sugestions as to why the hot coolant in the engine isn't circulating???? will a bad head gasket reduce the coolant pressure enough to stop it from circulating???- thanks Robby

[brivers]

Just a few ideas to check. Do you usually loose the heat from the heater while your driving? If you live in a very cold area and the thermostat is sticking open then your radiator can almost keep these motors cold. The fact that you checked you tstat is'nt always reliable. At what temperature did it open? The fact that you have heat at times would tell me that your heater core is relatively clear. I'm going to guess you need a new tstat. Not to scare you but frozen coolant can block flow. Just because the engine is running does'nt neccesarily mean it will thaw that easy. And of course low coolant level can cause problems, the heater is the highest spot in the system. Good luck.

[Johnny Mullet]

Sometimes after opening the cooling system (new rad and water pump) air can get trapped in the system. I had this problem after my head rebuild. I had to jack the front of the car so the rad cap was higher than the rest of the cooling system and run it with the cap off until all the air burped out. This process took about 30 minutes.

[leonbentz]

I have had trouble in the past with the heater core plugging up. The veins are very small and plug up easy. I solved that problem and replaced it. It sounds like your T-stat is giving issues, but I would check that first, before going into your heater core. Like Johny Mullet said, check and make sure all the air is out of your system too.

[redpepe]

coincidentally i'm having heat issues with my '91 1liter manual .... 325k .... worn out but still better than many. long story ... i don't want to bore folks. i replaced a rad fan motor switch and pressure cap and the heat rise has evened out in the old lower / normal range. my problems now only arise after a long hill climb or sometimes when idling after getting off the freeway. the fan and / or circulation will not bring the temperature back to normal. may be a partially opened tstat.

i will replace the tstat today and will order a water pump. i like to do repairs one item at a time if possible. the haynes manual shows the original tstat with an air bleed hole that should be mounted toward the top ... and i have not removed the old [original probably] one yet. the new tsat does not have a bleed and i've considered drilling one if desirable. i don't often need to fill the rad but it's no problem to 'burp' them at a fluid change.

[redpepe]

replaced the water pump .... the original inside looked like new! ... and am experiencing similar heater poor performance. the heat range indicated on the guage is very low now. a mystery for the moment. i'll replace the radiator when i find time .... and check the heater core ... but the system insides have all been spotless so far.

[brivers]

Assuming your temp gauge is working properly I don't think your radiator is the problem. Did you replace the thermostat? If anything your radiator is working too good. A plugged radiator would make your system hot. If your tstat is working properly the engine will warm up, because the only place for the coolant to go and get cooled is the heater core. I would focus on the tstat. Either it is sticking open or its bypassing it somehow. The only way I know that it can bypass it is the heater core, which it is supposed to.

[redpepe]

i didn't mean to hijack the thread but the problem is similar.

brivers: i've replaced the tstat and like rjm1000 i get intermittent symptoms. i noticed today that the rad is cool even when the guage is showing hot and the fan is running. this indicates to me a blockage but it only happens sometimes as far as i can tell. running down the freeway on the flat, the engine heat is fine though generally a bit cooler now since putting in the new parts. the heater only makes warm air and it used to be a furnace.

[brivers]

With all that said, I'd say its time to either flush or replace the heater core. I would flush first just to see if you had flow, and maybe even clear the sediment out. One other thing, my Metro does'nt have a heater control valve, so thats not really an issue in my case. Make sure thats not an issue with yours. (heater control valve is inline with one of the heater hoses that keep coolant from flowing through heater core) When flushing alternate the flow so as to break up sediment. Good luck.

[DOCTORBILL]

If I had your symptoms (all of you), I would....become Sherlock Holmes and use some deductive logic.

brivers is right - The cooling system is dog dirt simple.

Plugged radiator core ? Small tubes.
Plugged heater core ? Small tubes.
Plugged Thermostat ? Is it in backwards ?
Plugged Engine Galleries ? Small tubes.
Plugged Water Pump ?
Plugged TBI ? Small tubes.

Has anyone ever put in that stuff to plug coolant system leaks...?
Is it now a big "clot" ?

Drain the system - save the coolant in a clean bucket for later.

Learn the coolant direction of flow for each component !

Disconnect ALL the hoses - to heater, to radiator, take out Thermostat.

Check the hoses - are they all clear - run a wire thru them to see.

Using a garden hose, run water backwards thru each separate cooling system component - each into a clean bucket.

Observe if the backward flow is good - slow flow would indicate an obstruction.

I am concluding that you have some piece of material moving around intermittently
plugging up the system components.

My '90 Jeep Cherokee had a chunk of Rubber Hose the size of a big peanut
stuck in the input port of the Heater Core !

Backward flushing with my garden hose into a bucket proved that to me....

We (my wife helped me do this) also got about a quarter cup of big rust flakes which
could accumulate, break up and accumulate again in those small tubes.

Look for the crap in the bucket to prove to yourself that it was there.
Then take a picture to post here to show folks that "it can happen"...

It might even be some fiber that takes a while to accumulate and then breaks up and repeats.

If the Thermostat and Water Pump are good and if you have the hoses going to the correct places -
then what else could be wrong - unless you are superstitious and believe in evil spirits.

When you are all done, pour the drained coolant back into your system thru a double cloth filter.

DoctorBill

[redpepe]

hi bill et al,

good analytical process as usual and that's what brought me to this point. the fan had failed which triggered the investigation. the surprisingly clean system has lead me to look for uncommon problems though i don't mind replacing the radiator or any parts on a 325k engine .... which i'd do at a rebuild anyway. i am swamped with other projects and will need to resume the fix when time is available. anomalous and intermittent problems are the most intriguing.

not a fan of 'the invisible hand' or any evil spirits but always amazed as they predictably show up in most arguments.

the index seems like a terrific idea.

[redpepe]

for the moment it appears that the trouble has been the radiator fan. i've almost never seen an electric motor slow down v die completely. i'll be testing the system again today but i've had some interesting surprises along the way.

replaced all hoses and a new radiator. i may try reinstalling some of the original parts again since for instance i believe the new thermostat is not calibrated as accurately as the one i took out and i'm curious about the performance of the orig radiator since it seems as spotless internally as the entire system and i can't figure out why it might have reduced performance except that the fins might have an oxidized contact to the tubes which would reduce the heat transfer. i'm tempted to reinstall the old radiator for a test and put the new one on the shelf for the coming rebuild.

[brivers]

Getting a little confused with redpepe' problems and rjm's problems. Here is a general description of the cooling system that may help with cooling and heating problems.
Start the car; the thermostat is closed, no coolant circulates through radiator. Coolant is circulating through block and cabin heater core.
Engine warms up to the point where tstat opens.Coolant begins flowing through the radiator, Sometimes if tstat is sticking you may see temp gauge rise above you norm on the gauge and then fall as tstat opens. ( I have found that if a block or radiator sealer has been used in the system it can cause this or even tstat failure ) If you have this condition its time to change your tstat before it fails.
The tsat does'nt just open and stay open, it is constantly adjusting according to coolant temperature, but its job is to keep coolant temperature from falling below it design temperature.
The radiator is designed to keep temperature of coolant from exceeding engine designed temperature even at its extreme usage. High speed, going up steep inclines, alternator draw, ac, power steering, automatic transmissions, etc., all of these draw horse power which in turn require more fuel to be injected into the engine and create more btus of heat which must be removed from coolant. Yes friction has a role but its usually a constant. The radiator design has more power to remove btus than the motor has the capacity to make. (unless there was a design flaw from auto maker)
With electric fans, they are designed to keep air flowing through the radiator when there is insufficient air flowing, as in sitting still or very slow speeds. Its set point to come on is much higher than the tstat design. Some fans don't come on until coolant hits 210 degees or higher. If you engine is overheating going down the highway, the problem is not the fan. In fact, unless you sit in traffic alot or sitting still, your fan hardly ever has the need to come on.
Water pumps circulate coolant throughout. Maybe its me, but I have never seen a water pump go bad due to vane corrosion,(except in an industial situation) only seal or bearing failure. So, if your changing a water pump that does'nt have those two problems, your probably wasting your time. Yes I guess there are occurances of vane corrosion, but I beleive it to be rare.
If you don't have heat in the the cabin of you car, then chances are the coolant is'nt hot enough, (which means tstat failure) or somethings clogged (heater core, heater hoses, or heater control valve), but not your radiator.
If your overheating,when driving, then chances are tstat has failed, or somethings clogged. Radiator, engine coolant passages, hoses, Rare occasions spark timing, (if retarded). Head gasket failure could also be a culprit, but usually there will be other symtoms.
Hope this helps.

[redpepe]

thanks brivers .... good descriptions.

the heat would only rise after getting off the freeway or sitting still. i saw that the fan was not running and the fan switch was replaced and the fan began working again but the heat built the same way as before. i replaced the tstat and then the water pump .... and still the heat rise. after replacing the radiator, i noticed that the fan was varying in its rpm ..... but it was still turning. the diagnosis was prompted when the fan blew its 40 amp fuse ... probably from its growing disabilities and heat / load rise. incidently, when the fuse blew, the whole car shut down .... no electrical functions anywhere on the vehicle. keep a spare fuse! i replaced the fan motor and so far so good. i need to give it a good hill climb today if a get a chance. it's very rare in my experience that an electric motor does not simply quit completly when it's broken. it was turning but not enough to cool the radiator adequately evidently. fooled me. all the parts will be used in the coming rebuild so worth all the $$$.

[brivers]

Well Redpepe, you either typed the wrong size fuse amperage in your post or you blew a different fuse. Since it shut the car down I'd say it was your main fuse. With the small wires that power the fan, they would have been on fire way before a 40 amp fuse would blow.
If in fact it was your main fuse, you either have a 'shorted wire or electrical devise', or a bad connection at the fuse box under the hood. The main wire that powers the car has a heavier than normal slide/blade connector that looses it connectivity.