help! my cooling system is weird
Discussion
I've asked on the MX5OC and nobody seems to have any idea what could be up, hopefully someone here can help.
- Engine rebuilt (by me) after HG failure, head pressure tested and skimmed, genuine Mazda HG, new cambelt, waterpump, thermo (x2), rad cap (x2), new oil & filter.
- Fine for about 400 kms.
- From that point on after almost exactly 5 miles (from cold) the temp gauge shoots right up, then comes straight back down within 20 seconds, or if ignition turned off.
- Otherwise temp remains about half way, but seems to rises a tiny bit up hills, but not if I thrash it on the flat.
- has also completely filled the expansion tank 3 times now.
- Only does this seemingly every other journey - managed 20 miles this morning with no probs, in the evening it filled exp. tank and same temp gauge oddness.
- If left idling fan comes on and off and temp remains normal.
- Rad level remains just above cooling fins.
- Had sniff test done, coolant has no exhaust traces.
- Fitted 2nd new thermo, 2nd new rad cap, and a new temp gauge sender.
- Replaced coolant 3 times now.
Still this the problem remains exactly the same, and I am stumped.
Anyone have any ideas what could be up or what I can try next?
thanks
James
- Engine rebuilt (by me) after HG failure, head pressure tested and skimmed, genuine Mazda HG, new cambelt, waterpump, thermo (x2), rad cap (x2), new oil & filter.
- Fine for about 400 kms.
- From that point on after almost exactly 5 miles (from cold) the temp gauge shoots right up, then comes straight back down within 20 seconds, or if ignition turned off.
- Otherwise temp remains about half way, but seems to rises a tiny bit up hills, but not if I thrash it on the flat.
- has also completely filled the expansion tank 3 times now.
- Only does this seemingly every other journey - managed 20 miles this morning with no probs, in the evening it filled exp. tank and same temp gauge oddness.
- If left idling fan comes on and off and temp remains normal.
- Rad level remains just above cooling fins.
- Had sniff test done, coolant has no exhaust traces.
- Fitted 2nd new thermo, 2nd new rad cap, and a new temp gauge sender.
- Replaced coolant 3 times now.
Still this the problem remains exactly the same, and I am stumped.
Anyone have any ideas what could be up or what I can try next?
thanks
James
No I'm not, I guess that would make sense - something is making it heat up quicker when going uphill, but not enough to cause it to overheat at idle, so perhaps the previous HG failure has partially blocked the rad.
I think I'm going to have to remove the hoses again and try to flush the rad, problem is I don't have access to a hose pipe atm. I guess I can pour water in at least and see how it flows through.
It's costing me a fortune in coolant
Is there something I can fill the system with and run up to temp that will properly flush it through?
thanks
James
I think I'm going to have to remove the hoses again and try to flush the rad, problem is I don't have access to a hose pipe atm. I guess I can pour water in at least and see how it flows through.
It's costing me a fortune in coolant
Is there something I can fill the system with and run up to temp that will properly flush it through?
thanks
James
Edited by anonymous-user on Wednesday 15th August 22:58
It's the intermittent nature of the problem that's mystifying. When it overheats, have you checked if the bottom radiator hose is fully hot? If not, that would suggest that either the water pump is malfunctioning, perhaps because it's stalling with an air lock, or the radiator does indeed have a blockage, such that coolant isn't fully circulating.
Don't know why it only happens sometimes, though!
Don't know why it only happens sometimes, though!
JimSuperSix said:
I've checked the radiator a few times, and it's always hot along the top tank and slightly cooler along the bottom tank, but I've not checked the temperature of the bottom hose itself.
Bottom hose should be cooler than the top hose, if it's hotter something is very awryRichyvrlimited said:
Bottom hose should be cooler than the top hose, if it's hotter something is very awry
Agreed. My thinking was that if the bottom hose is cold or at least significantly cooler than the top of the rad while the engine is overheating, then that indicates a problem.On my car I thought I had an overheating problem after I too had fitted a recon head with new gasket, water pump, timing belt, etc. The temp gauge would climb too high with even moderate driving and then fall back if I backed right off. I changed the already new thermostat with no benefit and was considering re-stripping the engine when I relaised that even though the temp gauge was reading high, the bottom radiator hose was cold. I'd already fitted a new temp sender but had used a non Mazda part. I replaced it with a new Mazda sender and my overheating problem disappeared. A big relief but also v frustrating that a new part malfunctioned - one just assumes that these things will work as intended!
The rads rarely get completely blocked, they just get a partial blockage so they only overheat under heavy load (uphill, motorways etc.). Running water through it, even with a hose isn't likely to show anything up. It can be good to flush it through to see if any crap comes out but usually, once they have a blockage they need to be replaced.
You might be able to detect a blocked area by running it up to full temp then feeling all over the front of the rad for cold spots. It's not always that easy to feel though.
You might be able to detect a blocked area by running it up to full temp then feeling all over the front of the rad for cold spots. It's not always that easy to feel though.
Got a possible solution from the MX5OC forum, taken from a Miata tech document, so going to check this next as it matches the symptoms my car has exactly. If I've no joy here then perhaps a new rad.
Note the small hose at the bottom of the thermostat housing that carries coolant output from the cylinder head through the input side of the thermostat housing and down to the water pump input. This assures that hot coolant from the head flows through the thermostat housing when the thermostat is closed, exposing the thermostat valve to the coolant. If this path is blocked by metal shavings in the thermostat housing outlet nipple, or anywhere in the small hose, the coolant will not flow through, and the thermostat will not open early enough. A symptom of a blocked path here would be temperature rising above normal on first warm-up, then suddenly dropping to normal sometime later.
http://www.miata.net/garage/CoolingSystemProblems....
Note the small hose at the bottom of the thermostat housing that carries coolant output from the cylinder head through the input side of the thermostat housing and down to the water pump input. This assures that hot coolant from the head flows through the thermostat housing when the thermostat is closed, exposing the thermostat valve to the coolant. If this path is blocked by metal shavings in the thermostat housing outlet nipple, or anywhere in the small hose, the coolant will not flow through, and the thermostat will not open early enough. A symptom of a blocked path here would be temperature rising above normal on first warm-up, then suddenly dropping to normal sometime later.
http://www.miata.net/garage/CoolingSystemProblems....
MX-5 Lazza said:
Actually makes no difference on an MX5. The water flows through the heater element whether the heater is set to hot or cold, it's only the air-path that changes.
Didn't know that, but worth checking you feel warm air from the heaters before the cap goes back on so you know the water is circulating properly.Gassing Station | Mazda MX5/Roadster/Miata | Top of Page | What's New | My Stuff