Thermostat... or more?

Hi Fellow car talk listeners. Posting all the way from the UK and although I’m an avid listener, I am not very mechanical so go easy on me! Here is my question. After a deep freeze the other night, my car seemed to freeze up. I took it for a drive and was having severe boilover in the coolant overflow tank. Also, no heat coming into cabin. Car does not have temp gauge BTW. After some research, I decided my head gasket was gone, but my neighbor tested it with some pressure guage and said it wasn’t. There seemed to be some sludge in the radiator pipes so I have thawed it with a hair dryer, drained all the coolant and refilled. Same problem. Then after more reading, I unhooked the heater core hoses and ran water through them. Went through fine and came out clear! Problem still there. So after more reading decided it was thermostat. Pulled that out and sure enough it seems to have failed (will go get a new one in morning). BUT it has failed open. So my question is, can a thermostat, failed in the open position, cause coolant to boil (I thought not) OR is there still another problem elsewhere?

Many many thanks

I thiink it is very likely that your coolant concentration is not adequate for the recent low temperatures.

Believe it or not–and I know that this is counter-intuitive–a build-up of ice in the coolant passages of your engine can actually result in an overheating situation. And, it can also lead to a no-heat situation. While this may sound counter-intuitive, I have seen this scenario on more than one occasion. The presence of “sludge” tells me that the coolant is likely to be old and may have been over-diluted with water over the years.

So, if you drained the coolant and simply refilled the cooling system with the same coolant, the problem will not be resolved until you drain the old coolant and replace it with new, to the proper concentration for low temperature protection. Dilution instructions should be on the back of the jug of coolant. If pre-diluted coolant is sold in the UK, that is fine right out of the jug and will provide more than enough protection for UK winter temperatures.

Incidentally, it is possible for there to be damage to your engine from the combination of ice and overheating. I would suggest that you monitor the situation carefully after refilling with new coolant.

Thanks, I have now replaced all coolant with the right mix but the problem is still there. Unless there is a blockage that I can not find. Is there anyway to diagnose a blockage other than what I have tried?

It could also be that your water pump is not circulating the coolant properly. That would explain both the boiling and lack of heat inside the car. The water pump has vanes (usually metal vanes) that can corrode over time if the coolant is not drained and refilled with fresh coolant every few years or so. The vanes can be eaten away entirely in severe cases. (I believe there are some water pumps with plastic vanes that can break, too, but I’m not sure of that.)

You might test this out by re-installing the stuck-open thermostat (so that your test will work on a cold engine), disconnecting one of the hoses, putting the end in a bucket, and running the engine briefly to see how much coolant flow the water pump is putting out.

hmmm… I fear you may be right. First, I just ran the car without a thermostat altogether. Still overheated. I disconnected the return hose (to the reservoir) Nothing! I’m not sure how long it should take to return but…
Could a blockage not create the exact same symptom though? If it is broken pump, is this something I will be able to replace with my lack of knowledge (I am good at research). Cheers.

Never heard of a “blockage” stopping coolant flow inside an engine block. If you’re saying you ran the engine with the thermostat open (or missing) and no coolant came out of the top (return) hose to the radiator, my first guess would still be a bad water pump.

I’ve never changed the water pump in a Festiva, but it’s probably driven by the camshaft timing belt, which is easy to reinstall incorrectly if you haven’t done it before. So I wouldn’t recommend trying it yourself unless (a) you have plenty of spare time, (b) you don’t need the car to run for a while, and © you have a high tolerance for failure. Also, if this is an “inteference” engine and you get the timing belt on wrong, you may wreck the engine altogether.

If your radiator had slush or ice in it , that would cause overheating.

If you had plain water in your cooling system, draining it and refilling it with 50/50 mix might not give you a strong enough mixture. A better wat is to flush everything out with plain water and drain. Then fill with full strength coolant in the amount of 505 of your cooling system capacity, fill the rest of the way with water. Then do the same thing with the recovery tank.

Thanks oldtimer. The only way to fill the radiator seems to be via the recovery tank. But since I have drained, refilled and let the engine run, the ambient temp has been high enough that I think it would have thawed out. I made the most recent mix more like 60/40 to compensate for any ice that have been lurking. Is there any way to ‘flush’ the radiator via the hose inlet/outlet just to be sure… before I arrange for it to be towed to a mechanic?

Yeah my guess is you didnt have proper mix of coolant and it froze or got slushy as you said and you drove it without it being able to circulate which caused it to over heat and no heat from heater. Get it in a warm garage over night. run it the next day. Make sure it warms up good. Then check your coolant for mixture. (Dont open radiator cap when hot) You want 50/50 Water n coolant

Unfortunately, there are no warm garages near by. If this can be troubleshot and fixed in a 7-20 degrees (f) range, it really needs to be (I know that’s not cold for many of my American counterparts, but it is for us!) :frowning: I live in the stix.

I certainly sense some type of engine damage here (like exhaust gases in the coolant). The block is not restricted due to ice and your “boiling over” is not related to any error in water/antifreeze mixing as there should not be any boil over with straight water. Ask at your parts store for a kit to test for the presence of hydracarbons in the coolant. Compression check may show something out of order. Just how severe and long was this “boil over” incident? this is not good.

you fill me with a lack of hope oldschool! If I run the engine without any gas applied, maybe 8 minutes. If I give it some gas, maybe 4. As for severity, it boils and steams out the overflow tank quite violently. There are somethings I have noted but not added that may be useful. There is a faint smell of coolant when blowing the air in cabin and I just went and sat in car and there is a 1/4 of ice INSIDE the car on window. There car is ‘sealed’. Could this have been from my heater core flush? Other than a blown head gasket what kind of engine damage could have appeared overnight? Many thanks

I have noticed that the radiator fan is not coming on. Could this be the cause? (bump/HELP/thanlyou)