Here's the deal. Bought the car used. Put a new engine in it. The car overheats and there is no heat from the heater. Here is what I've done:

New upper and lower hoses.
New thermostat.
New AST cap, 13 psi.
New hose from water housing to heater core.
New heater core to replace what should have been the old leaking one.
New screw clamps on everything.

Sometimes there is a puddle around the rear of the pax wheel. Sometimes not.

There was some antifreeze on the floorboard (hence why i changed the heater core).

I don't see any leaks or smoke from antifreeze hitting something hot - nothing. After 5 or 10 minutes, temps start to go high, buzzer goes off, and either way, there is no heat from the heater.

Ideas?

 

no blockage in the radiator either.
it seems all that is left would be the water pump is not spinning...

 

You may need to "burp" the system. A lot of air left in the system may cause what you are seeing. Search for "burp" and a lot of threads will come up to help you figure it out.

 

yeah, burping has been done.

pulled the hose which goes from the water pump housing to the heater core, and let it dangle. started car - no fluid is coming out. i assume now the water pump is not pumping...

 

I'm still new to this but of your not getting any heat from the heater, doesn't it have something to do with thermostat?

 

I seem this one before, but not on a rx7, it was on military hummer. The problem was like yours. The enigne over heat, but The radiator is still cold when the truck is overheating. So just seems like the coolant is not cycling in the system. you did not mention anything about your radiator, but please check that and see if yours is cold when the engine is overheating.
What ended being the problem was the small hose that vent form the top of the radiator to the overfill tank is clog up by silicone. The truck just got a new water pump put it, and the tech went crazy on the rtv and some work loose and got in the line. This cost a big air pocket in the radiator, and pervent the system to cycle its coolant.
o.k. enough bs form me, just check your AST vent line, the top and bottom one, and see if it is clog up. since you just got a new engine. the tech might have done the same thing.
I am not sure if the heatercore on our 7 has a vent line, but if there is check that one too.

good luck.

 

yeah, that's where i started, with a new thermo. then a new heater core (or used, but i know it works) (and the old core shows no signs of blockage or leaks).

so i pulled the water pump. spin it and it squeaks a bit, so i'm hoping it's a bad bearing and a new pump will solve the problem.

 

chinoflyer - thanks. good points. will do...

 

Here's a stab in the dark.. Do you have aftermarket pulleys? Are you sure you belt is routed properly?

 

Thermostat installed backwards?

 

U might be missing a heat hose. Does this happen? even on hot days the air that comes out is only slight hot?

 

belts are good, thermo is in correctly, all hoses accounted for.
going to install different water pump tomorrow and see what happens.

 

i forgot to mention to check your ast nipple, if there is a clog, it may not always be in the hose itself, could be the small nipple that the line is on.

good luck

 

Are you sure the thermostat actually works? Did you check to see if the radiator gets hot? If the thermostat is not opening then the coolant will not flow into the radiator and the radiator will stay cool.
A squeaky bearing in the water pump will not cause the car to over heat, unless the water pump completely fell apart the only problems it could cause is a leak and make noises. Dont change the water pump thinking that will resolve the over heating problem.

 

good point - i think i need to run the whole thing without the thermo installed and see what happens.

 

You will still get heat from the heater if the thermostat stays closed - but the car will overheat and the radiator will (mostly) stay cold.

 

Your no heat deal is weird. Check to see if your radiator gets hot (telling you the thermostat is good) then check to see if your fans are coming on properly.

 

it's gotta be the thermostat. New water pump (well, a different one, at least), burped the system - but the radiator hoses, heater hoses, and radiator itself are all cold (car still overheats).

When it cools down, gonna run it without a thermostat at all, and see what happens.

 

my waterpump squeeks while turning it by had as well, its just the seals, shouldn't be a problem

 

sounds like either a thermostat or a huge blockage in the cooling system, hope for the prior...


if pulling the thermostat doesn't fix it then i can only suggest pulling all the major hoses off and blowing through them to try and find the source of the blockage.

 

Could be you bypassed the heater core?! I had to cause my core cracked while driving and been bypassed since, so no heater for me.

 

i havent read the whole of this thread, but i had this problem when my coolant seals went. Warm car - cold air.

Start the car from stone cold for 30 seconds. Switch it off. Squeeze the top rad hose (the one coming from the bottom of the filler neck) if it is hard, i suggest your coolant seals have gone. Open the cap - if there is pressure in the system when the car is cold, this is bad. Also smell the filler neck - if there is smoke in there and it smells of exhaust, you know what your problem is.

 

I also think its your thermostat sticking closed.

 

I would also like to know the answer to this. I have the same problem. Although, my radiator gets hot, proving that there is coolant moving through it. However, my heater core is ice cold. Thermostat was changed twice and the water pump was replaced. Could it possibly be that the both thermostats and wate pump are bad?

If the cooling system was blocked, wouldn't one of the lines burst open?

 

Ok, problem solved.

2 thermostats were bad. One was the original which was working at one point, the other was a new one from NAPA.

Ran it without a thermostat installed, no overheat, and the heater works. Unfortunately, now there is a leak at the brass tube junction for the heater core. ugh.

In the end, my lesson for everyone:

Before going crazy with a problem similar to this - run the system without a thermostat. I could have saved A LOT of time and effort if I had just done this first.

Thanks for everyone's help. If anyone knows an easy way to stop a brass junction from leaking, let me know!