Heater flow/temp issue?

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1990Z71Swede

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Soo, With European studded Snow tyres on, and the wonky power steering now fixed. This is an AMAZING ride in the Winter. Every bit as fun as the old Audi Quattro I used to have years ago, just with a LOT more Cowbell :)
Except... Cabin Heat.
It is not cutting it. Apparently when it works it is supposedly very efficient, not so much on this truck though.

So far I have flushed the heater and backflushed the QD on the intake going to the heater, including the hoses to and from the heater. There were no signs of blockage anywhere really and the water coming out of the heater was clean.

What I have noticed so far is engine temp is not stable and fluctuating between maye 60-90 degrees centigrade. But it is difficult to say really becase the scale on the gauge is a bit weird. I'm going to start with replacing the Thermostat with a 195F from Gates.

Also, the hose going into the heater is only hot...ish I can hold it but I'm not sure my wife could :). The same hose on the 2008 Suburban is somewhat hotter, hot enough that I can't hold it very long.

The hose coming out of the heater in the truck is maybe luke warm, on the Burb it is significantly hotter.

The blend door actuator seems to be working fine and the fact that the heater return water is not hot points to a flow problem and not an actuator issue.

I've topped up the coolant and tried to bleed the system with the truck at an incline to rule out air pockets which did not change anything.

So what should be my next move? Maybe the new thermostat will fix everything? (I doubt it will but I think it is part of the problem at least)

Is a clapped out water pump a likely cause on these engines? (1990 350TBI) It does not leak or show any other signs of mechanical distress though.
 
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Schurkey

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Sounds like a thermostat that isn't working properly. 60C--90C =140F--194F. Not only should it not be cycling, it's just plain too cool except at it's hottest.

Replacing whatever thermostat you have with a 195F unit is wise. Would be interesting to see what's in there now. 160? 180?

Keep in mind that the coolant flow through the heater core is deliberately restricted by the quick-connect fitting. You don't need a lot of heater-circuit flow to get great heat.

Doesn't take anything special to remove air from the cooling system after cooling system service. The air naturally moves to the high-point the moment the thermostat opens...the high-point on these trucks is just under the rad cap. Air there is seen as "low coolant level".

Do you have adequate air flow? Pine needles, seeds, mouse nest, etc. up against the A/C evaporator will reduce airflow.

If the water pump had issues, I'd expect higher engine temperature. So water pump failure is not my first suspect here. Thermostat is.

My truck had rotted foam seals on the HVAC ducting, in particular the one between the steel cowl and the plastic inlet to the blower motor. Massive cold-air (winter) and hot-air (summer) leakage into the cabin.
 

1990Z71Swede

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Alright, that makes me a little bit more confident in the simple thermostat fix doing the trick.

Regarding adequate air flow I would say probably not, also the fan is making a little bit of "please gimme grease" noises so eventually it is going to need some attention I guess.

A car stereo is on its way too, so maybe I will take a look at the fan while I'm in there. Anyway thanks for the advice so far, it's been a great help.:worship:
 

454cid

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I've had to replace the thermostat on my last 4 vehicles right away. Both my Volvo's, the Buick Electra, and the Saturn.

Make sure you get a gasket too... 1990 might be paper. Make sure you get all the old gasket off. GM switched to a rubber o-ring type at some point, but I don't know when. Those are a lot nicer to deal with.
 

L31MaxExpress

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I've had to replace the thermostat on my last 4 vehicles right away. Both my Volvo's, the Buick Electra, and the Saturn.

Make sure you get a gasket too... 1990 might be paper. Make sure you get all the old gasket off. GM switched to a rubber o-ring type at some point, but I don't know when. Those are a lot nicer to deal with.

Not sure on the trucks but both the 87 and 92 G20s I had used the rubber seal. I assumed all TBIs used them. The easy way to tell is if the thermostat is sloppy in the intake it uses the rubber seal. I have seen people throw the thermostat in with a paper gasket leaving a gap around the thermostat leaving a gap for coolant to continually circulate. Then it runs too cool. I have used the better Oreilly Murray line for years. Its a few $ more, but much more accurate than the basic one.
 

1990Z71Swede

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Alright, that makes me a little bit more confident in the simple thermostat fix doing the trick.

Regarding adequate air flow I would say probably not, also the fan is making a little bit of "please gimme grease" noises so eventually it is going to need some attention I guess.

A car stereo is on its way too, so maybe I will take a look at the fan while I'm in there. Anyway thanks for the advice so far, it's been a great help.
Not sure on the trucks but both the 87 and 92 G20s I had used the rubber seal. I assumed all TBIs used them. The easy way to tell is if the thermostat is sloppy in the intake it uses the rubber seal. I have seen people throw the thermostat in with a paper gasket leaving a gap around the thermostat leaving a gap for coolant to continually circulate. Then it runs too cool. I have used the better Oreilly Murray line for years. Its a few $ more, but much more accurate than the basic one.
Ok, are you steering me away from Gates? I thought they where one of the good ones? I live in Sweden so my options are somewhat limited compared to yours. :( Oreillys do not exist here for example.
 

454cid

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I beleive the Gates thermostat will be a rebranded Stant. However Stant has been purchased by Motorad, and Motorad's products are hit and miss. Motorad makes a lot of Orielly's cooling products. A thermostat from Motorad, Gates, Stant is probably ok. I've purchased a few Motorad thermostats and they've been fine. I don't know if Motorad has comepletly replaced Stant's thermostats with their own or not. Stant used to be one of the best brands.
 

L31MaxExpress

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I beleive the Gates thermostat will be a rebranded Stant. However Stant has been purchased by Motorad, and Motorad's products are hit and miss. Motorad makes a lot of Orielly's cooling products. A thermostat from Motorad, Gates, Stant is probably ok. I've purchased a few Motorad thermostats and they've been fine. I don't know if Motorad has comepletly replaced Stant's thermostats with their own or not. Stant used to be one of the best brands.
10+ years ago I ran only Delcos but they are no longer OE parts from them.
 

1990Z71Swede

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10+ years ago I ran only Delcos but they are no longer OE parts from them.
That is what I normally go for when shopping Chevy spares, but what you say explains why I could not find Any AC Delco thermostats.

Fun fact: Here in Sweden a Gates Thermostat is 20 $. On the other hand, the Benz thermostat that I had the dealer change was like 200 $:eek:
 

PlayingWithTBI

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Robert Shaw 194° high flow T-Stats have been pretty much the "go to" brand.
www.flowkoolerwaterpumps.com/collections/thermostats/products/robertshaw-330-160-degree-thermostat?variant=9125073322036


I've also used Mr Gasket (180° in my truck currently) high flow too.

www.summitracing.com/parts/mrg-4364?seid=srese2&utm_source=bing&utm_medium=cpc&utm_campaign=Brands+|+M&utm_term=4581321367343998&utm_content=GSAPI+5d1a2e78def6d

 
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